Secrets of 5-Axis Machining

KarloApro

I S B N 9 7 8 - 0 - 8 3 1 1 - 3 3 7 5 7

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Secretsot S-Axis

Machining

by Karlo Apro

Industrial Press, Inc.New York

Library of Congress Cataloging-in-Publication DataApro, Karlo.

Secrets of s-Axis lvlachining / Karlo Apro.p . cm.

Includes index.rsBN 978-0-8311-3375-71. l4achine tools--Numerical control. 2. Machining. I. Tit le. IL Tit le:

Secrets of 5-Axis Machining.TJ11B9.A68 20OB67 1.3'5--dc22

2004027254

Industrial Press, Inc.989 Avenue of the AmericasNew York, NY 10018

First Print ing, August, 2008

Sponsoring Editor: lohn Carleolnterior Text and Cover Design: Paula AproDevelopmental Editor: Robert E. GreenProduction I\4anagen lanet Romano

Copyright O 2009 by Industrial Press Inc., New York.All rights reserved. This book, or any parts thereot may not be reproduced, stored ina retrieval system, or transmitted in any form without the permission of the publisher.All trademarks and registered trademarks, including Mastercam@ and Vericuto, areproperty of their respective owners. All rights reserved.

STATEMENT OF NON-LIABILITYNo l iabi l i ty is assumed by the author or publisher with respect to use of informationcontained herein, including for any loss of profit or other commercial, special, orincidental damages. While every reasonable precaution has been taken in preparingthis book, the author and pubiisher assume no responsibi l i ty for errors or omissions.Publication of any data in this book does not constitute a recommendation orendorsement by the author or publisher of any patent, proprietary r ight, or product,

1 0 9 B 7 6 s 4 3 2

Printed by Thomson Press India Limited

Dedication

This book is dedicated, in loving memory/ to my mother Piroska. She taught methe meaning of hard work and perseverance. Although she passed away before thecompletion of this book, her spirit continues to l ive with me.

Acknowledgements

I would l ike to thank Yavuz lvlurtezaoglu for giving me the inspiration to write thisDOOK.

A special thanks to Laura Norton for her humbling insights.

And above al l , I would l ike to thank Paula Apro, my hard-working wife, fr iend, editotdesigner, and manager. For without her this book would never have come to be.

All the images in this book, including the virtual machines, were modeled usingf4astercamo (CNC Software, Inc.). The virtual machines were brought to l i fe usingthe machine simulation capabil i t ies of 14achSim (l" loduleworks) and VERICUT6(CGTech).

For more information on theseCNC Software/Mastercam671 Old Post RoadTolland, CT 06084860.875.5006www.mastercam.com

products or companies please contactlMachsim/ModuleworksModuleworks GmbHRitterstr, 12 a52072 Aachen, Germany+49.241.4006020www.moduleworks.com

CGTech/VERICUT9000 Research DriveIrvine, California 92618949.753.1050www.cgtech.com

For more information on the author, Dlease visit www.mult iaxissolutions.com

Table of Contents

I n t r o d u c t i o n . . . . . . . . , . . . 1

C h a p t e r 1 : H i s t o r y o f s - A x i s M a c h i n e s . . . . . . . . 3

C o m m o n l 4 i s c o n c e p t i o n s . . . . , . . . . . . . . . . . 4

R e a s o n s t o l J s e M u l t i a x i s l \ 4 a c h i n e s . , , , . . . . , B

C h a p t e r 2 ! K n o w Y o u r M a c h i n e . . . . . . , , , . , . . 1 3

l 4 u l t i a x i s l \ 4 a c h i n e C o n f i g u r a t i o n s . . . . . . . . . 7 4

T a b l e / T a b l e M u l t i a x i s l 4 i l l i n g f 4 a c h i n e s . . . . . . . . . . . . . . 1 8

I \4ach ine Ro ta ry Ze ro Pos i t i on ( l v lRZP) . . . . . . 21

N e s t i n g P o s i t i o n s , . . . . . . . . . . . . 2 6

Rotary Table Dynamic Fixture Offset . . . , , , , , , , . . . . . 27

H e a d / T a b l e M u l t i a x i s l 4 i l l i n g l v l a c h i n e s . . . . . . . . . . . . . . 3 1

H e a d / H e a d M u l t i a x i s l v l i l l i n g l 4 a c h i n e s . . . . . . . . . . . . . . 3 6

F i n d i n g t h e P i v o t D i s t a n c e . . . . . . 3 7

4 - A x i s l \ 4 a c h i n e s . . . . . . . . . . . . . 3 S

Geneml l4aintenance & Issues for 14ult iaxis lYachines . . . 40

I\4i l l ing l4achines With Five- or l .4ore-Axes. . . . . . . . . . . . 43

C h a p t e r 3 : C u t t i n g S t r a t e g i e s . . . . . . . . . . . . . . 4 5

iG

O*=

Chapter 4r Indexing Multiaxis Toolpaths . . . , .49

I n d e x i n g l v l e t h o d s . . . . . . . . , , . 5 1

How CAD/CA|V I Sys tems Hand le Index ing Work . . . . . . . .

Machine Coordinate Systems . .

lulachine Home Posit ion . .

Active Coordinate System . . ,

I \4achine Rotary Center Point , .

CAD/CAM System Origin . . .

Synchronizing lYachine and CAD/CAM coordinate Systems .

56

60

60

Chapter 5: Simultaneous Multiaxis Toolpaths. ,65

T h e O p t i m u m W o r k E n v e l o p e . . . . . . . . . . . . 7 0

F e e d r a t e s . . . . . . . . , , 7 2

I n v e r s e T i m e F e e d r a t e , . . . . . . . . , , , . . . 7 4

P o s t P r o c e s s o r s . . . . . , . . . . . . . . 7 6

Chapter 6: Common simultaneous Multiaxis cAMT o o f p a t h C o n t r o l s . , . . . . . 7 9

C u t P a t t e r n s . . . . . . . . 7 9

T o o l A x i s C o n t r o l . . . . . . . . . . . . . 8 6

T o o l T i p C o n t r o l . . . . . . . . . . . . . . 9 0

C o l l i s i o n C o n t r o l . . . . . . . . . . . . . 9 3

A d d i t i o n a l M L r l t i a x i s I s s u e s a n d C o n t r o l s . . . . . . . . . . . . , 9 8

D o v e t a i l E f f e c t . . . . . , . . . . . . . 9 8

C u t t i n g D i r e c t i o n . . . . . . . . . . 1 0 0

I v l u l t i a x i s R o u g h i n g . . . . . . . . . 1 0 1

C h a p t e r T r M a c h i n e S i m u l a t i o n . . . . , . . , , . . , 1 O 3

G - c o d e S i m u l a t i o n V e r s u s C A M S i m u l a t i o n . . . . , . . . . . 1 0 5

C o n f i g u r i n g V i r t L r a l M a c h i n e s F o r S i m u l a t i o n . . . . , . . . . 1 0 5

V i r t u a l M a c h i n e B u i l d i n g . . . , , . . . . . . , . . . 1 0 6

T h e S k e l e t o n . . . . . 1 0 6

C o m p o n e n t s v s . l t 4 o d e l s . . . . . . , . . . . . . I 0 7

M a c h i n e S i m u l a t i o n I n t e r f a c e s . . . . . . . . . . 1 1 6

U s i n g M a c h i n e S i m u l a t i o n . , . . . . . , , . . . . 7 I 7

Chapter 8: Selecting The Right Machine For yourA p p l i c a t i o n . . . . . . . . . . . 1 1 9

Head/Head Machines (with long X or y - axis linear travel,b u t l i m i t e d r o t a r y a x e s t r a v e l ) . . . . . . . . , . I 2 1

Head/Table l4achines (with long X-axis travel) . . . . . . . I23

H e a d / T a b l e l 4 a c h i n e s . , . . . . . . 1 2 6

R o t a r y T a b l e - T i l t i n g H e a d C o m b i n a t i o n s . . . . . , . . . . 1 2 8

T a b l e / T a b l e l v i a c h i n e s . . . . , . . . . I 3 2

Gan t ry Type Head /Head l v l ach ines . . . , . . . . L34

Chapter 9! Choosing a CAD/CAM System For yourA p p f i c a t i o n . . . , , . , . . , , , t g 7

S p e c i a l P u r p o s e S o f t w a r e . . . . . . . . . . , , . . f 3 7

C A D / C A I 4 T o o l b o x . . , . . . . . . , , 1 3 9

M u l t i a x i s c A D / C A l v l C o n s i d e r a t i o n s . , . . . . . 1 3 9

M u l t i a x i s C A f 4 . . , . . . I 4 O

l 4 u l t i a x i s C A D / C A I 4 T . a i n i n g . . , , . . . . , , . . I 4 4

Behind the Scenes: CAD/CAM Software Development . . 145

General Guidelines for Researching CAD/CAM Software. . 146

Chapter 10: Putting ItAII Together, . , , . . . . .149

W h y U s e l 4 u l t i a x i s l v l a c h i n i n g T e c h n i q u e s ? . . . . . . . . . . 1 5 2

W h a t i s a S t a n d a r d s - A x i s l \ 4 a c h i n e ? . . . . . . 1 5 3

W h a t i s t h e S t a n d a r d A x i s C o n v e n t i o n ? . . . . . . . . . . . . 1 5 4

What are the Three Major Mult iaxis f4achine Types? . . . 154

What are the l ' . lajor Building Blocks of a CNC l4achine? .

What are the 14ost Important Physical Posit ions of a[4ult iaxis 14achine?

What Tools are Needed to Find MRZP?. . .

Descript ion of Indexing/Rotary Posit ioning Work. . . . . .

Whal i5 a Post Proccessor?.

DefiniLion of an Axis

Defining a Simultaneous 5-axis Toolpath

What are the Three Common Simultaneous lYult iaxis CAMToolpath ConLrols.

14ult iaxis Machine Offsels. . .

Finding lYachine Rotary Zero Posil ion. . .

Finding the Pivot Distance

I n d e x i n g / R o t a r y P o s i t i o n W o r k O v e r v i e w . . . . . . . . .

Picking a CAD/CAM System for Multiaxis Work . . . . . . .

14achine Simulation .

Conclusion

156

157

159

159

159

160

160

161

167

162

164

166

166

167

767

Introduction

Are you uti l izing 5-axis machining? Could your shop benefit from the eff iciencyand power that 5-axis machining offers? The majority of people not embracing thistechnology lack a true understanding of 5-axis practices. There are many commonmisconceptions on the subject, and the intent of this book is to demvstifv 5-axismachining and bring it within the reach of anyone interested in using the technologyto i ts ful l potential. The information presented in this book was gathered during30 years of hands-on experience in the metal-working manufacturing industry -bridging countries, continents, and mult iple languages (both human and G-code.)The author worked in Hungart Germany, Canada, and the USA, special izing inmult iaxis solutions, He spent many years sett ing up, programming, and reparnngCNC equiprnent, and has used a number of different CAD/CA|Y systems. He hasworked as a self-employed mult iaxis consultant, as well as djrecuy for CGTech (themakers of VERICUT@) and CNC Software Inc. (the makers of t tastercamo.)

The author has instructed countless mult iaxis training classes over the past decade,These classes covered topics such as operating CNC equipment, programmingCNC equipment, both manually and with CAD/CAM systems, and bujlding virtualmachines with different verif ication systems. Through the years, the author has metmany professionals around the world and has come to a realization that they atlhave the same questions, misconceptions, and concerns, when it comes to 5-axismachining. The need for unbiased information on the subject became apparent.

Up to this point, the best way to get information on 5-axis machining was to talkto peers in the industry in the hope that they would share what thev had learned,Visit ing industrial trade shows and talking to machine tool and CAD/CAI4 vendorsare other options - except that these people al l give their individual points of viewand wil l promote their own machine or solution. Everybodv claims to have the bestmouse-trap, and it is left to the individual to choose the right one.

This book is not a training manual for any part icular machine or CAD/CAM system.Rather, i t is an overview of mult iaxis machine tyDes and the common controlmethods that CAD/CAM systems use to drive the machines. The book wil l guide youthrough this realm, from basic to complex concepts, and wil l provide informationto help you choose the right tools, including the machine, work-holding method,CAD/CAM system, and machine simulation package that wil l best suit your specif icapplication. The book contains numerous i l lustrations to help you to preciselyimplement these tools.

History of S-Axis Machines

Long before CNC control lers appeared,4-5-6-12- and more-axis machines, referredto as mult iaxis machines, were being used. Ihe individual axes were control ledmechanically through levers r iding on cam plates. Some machines had more than 12cam plates, control l ing not onJy tool/table and rotary motions, but also clamprng andunclamping of work-holding f ixtures. These machines were cumbersome ano atmeconsuming to set up, but they were perfecUy suited for mass production.

The f irst NC (numerical control without internal memory) machines werecumbersome to set up and operate, but they also were great for mass production. Atf irst, only the most aff luent and established shops could afford them. programm,ngwas a lengthy, error-prone process. Soon, machine builders added intern;l memoryto their control lers, then they added the abil i ty to execute simple branching loopinglogic, and to calJ subroutines from other subroutines. It was possible to us; thesemacro languages directly on the machine and to quickly change set_Lrps, especial lyfor family type parts. Different machine builders developed various solui ions, whichcreated a number of CNC (computer numerical control with internal memory)programmrng tanguages. Companies with famil iar names l ike Fanuc, Acramatjc,Heidenhein, Siemens, I\4azatrol, etc., al l developed their own languages, butthese quickly became an issue. Some shops ran ten machines wiih eigfrt Oifferentlanguages. If a repeat job came in, and the originally programmed michine wasbus, a new program would have to be re-writt in from sc-ratch because of thelanguage differences.

N.ext,-the f irst.rudimentary CAD (Computer Aided Design)/CAM (Computer AidedlYanLrfacturing) systems were devejoped. At f irst, these software solui ions wereintroduced by the same companies that developed the control lers. Soon after,enterprising individLrals wrote their own CAD/CAI4 software. This jump in tecnnorogywas huge because it al lowed engineers to draw their parts in a CAD program,generate a toolpath in the CAM systemt generic language, and then translate i t intomult iple G-Code languages quickt, using the appropljate post processor.

This progress meant that CNC machines were no longer the exception, and tneystarted to become the norm. They were no longer used only for mass_production andthey became versati le, accurate, and affordable.

Ivlult iaxis machines went through a similar process, but because thev were morecomplicaled, this process look longer. First, Ihe machines were expensive to

purchase and maintain, and harder to program, Only large aerospace companieshad the need, the money, and the personnel to handle multiaxis applications. Somecompanies kept their own processes closely guarded in order to gain an advantage,Many software packages were born out of necessity - in order to solve specificapplication challenges. Software, in general, is always on the very leading edge oftechnology - pushing the limits of software possibilities and hardware restrictions.

Today, there are many machine builders offering a variety of multiaxis equipmentin a wide range of configurations, quality, and price. Computers have become veryaffordable, and CAD/CAM systems now offer excellent multiaxis cutting strategieswith great tool control and large post-processor libraries. As a result, even smallershops can, and do, implement mult iaxis machining.

Most machine bui lders are expanding product ion and embracing new technology,Many believe that it is imperative to compete in the global market, especiallyagainst countries with abundant cheap labor. This attitude has resulted in increasedmult iaxis machine sales and some machine bui lders now have wait ing l ists ofcustomers for mult iaxis machines, Mult iaxis machining is a constant ly expandingf ie ld, wi th almost endless possibi l i t ies.

Common Misconceptions

Most people associate the word "s-axis" with complicated motions such as thosefor the induct ion pump i l lustrated in Figures 1-1 and 1-2, and the programmingtechniques needed, This view is reinforced by visits to any industrial trade showto see both machine builders and CAD/CAM vendors showino off their mostcomplicated creations.

Figures 7-7 Example of induction pump set-up

Secrets of s-Axis Machining

Figure I-2 Example of induction pump design.

In reality, the majority of s-axis users don,t ever make an impeller, or finishports for a.racing-engine cyrinder head. Most of them machine paris using simpre3-axis drilling, contouring, and pocket milling routines, while roiating the-part'occasionally in a rotary indexing mechanism, as illustrated in Figurei 1-3 and 1-4.very elaborate parts can arso be machined by apprying 3D surfa-cing toorpaths andengaging the part from different angles by indexing a rotary table.

-

Figures t-g and l-4 Examptes of positioning work.

Using a multiaxis machine will greatly simplify the motions required, theprogramming effort, and the amount of fixturing needed for machining complexworkpieces. other benefits include the eliminati-on of multiple set-upsf increasedaccuracy, and better surface finish.

History of s-Axis Machines

common Misconceptionr I don't ilo enough S-axis work to warranta S-axis machine.

Many shops are current ly making parts by moving them manual ly to di f ferentfixtures on 3-axis machines. Compared with this procedure, production can beincreased great ly without much effort by using a 4- or a 5-axis machine. I f s imply asingle- or dual-rotary indexing table was added, only s l ight edi ts would be neededto the CNC-code f i les. ExamDles are shown in Fiqures 1-5 and 1-6.

Figures 7-5 and 7-6 Third-party rotary mechanisms.

Moving to mult iaxis machining requires thinking in space instead of in a f lat plane.Dedicated mult iaxis machines have been developed for the kind of indexing workshown in the accompanying Figures 1-7 and 1-8, using tombstone type f ixtures.

Figure 7-7 Example of tombstone fixture.

Secrets of s-Axis Machinino

Figure 7-8 Example of 4-axis positioning.

Once you enter the mult iaxis realm, new doors wi l l be opened for your shop. yourcompany wi l l quickly become more adept and able to tackle more comDlex work.Before too long, your shop wi l l start taking on more and more jobs, and wi l l needto be exoanded.

Common Misconception: S-axis CAD/CAM is too expensive and ishard to use,

The above statements were true in the past, but not any more. If you currenflyown a CAD/CAM system, there is a good chance you already have s-axisposi t ioning capabi l i t ies. Most cAD/cAM systems include these caDabi l i t ies in theirbase package. Many t imes, i t is just a matter of t raining that is needed to get upand run n i ng .

When you are shopping for a CAD/CAM system, make sure to choose one from areputable company with a commitment to t raining and local support . Rememberthat a CAD/CAM system is just another tool in your tool belt. you can buy fancytools that are very capable, but they are worthless if Vou don,t know how to usethem. Great local support may very well be the most important feature of vour newtool .

Historv of s-Axis Machines

If you do a lot of simultaneous multiaxis work, the price of the CAD/CAM will beonly a smal l factor. More training wi l l be needed, but you wi l l be able to chargealmost double for your hour ly machine t ime. The'hard to use'paft a lways comesdown to training - was it easy to learn how to operate your first CNC machine?

Don't enter the mult iaxis world by start ing with a complex, s imultaneous job. I fyou already own a 3-axis machine, start wi th a single- or dual-rotary table andapply indexing techniques. You will make parts faster and more accurately, and youwi l l be able to invest in more equipment. When you decide to buy new equipment,see if you can bundle a CAD/CAM purchase with the machine's purchase order.This is also a good time to make sure your CAD/CAM system speaks your specificmachine's language - in other words, that it has the correct post processor.

Some companies buy equipment with a turn-key solut ion, which ensures that theirspecific job will run on the machine upon delivery from the manufacturer. Manymachine tool bui lders employ capable teams of appl icat ions engineers, who inturn, work closely with CAD/CAM developers, Together, the teams determine themost efficient way to machine any specific part, based on many factors such as;mater ial , quant i ty, to lerance requirements, and tool ing avai labi l i ty.

Reasons to Use Multiaxis Machines

Reduced Set Up workOne important reason to use multiaxis machines is to reduce set-up time for partssuch as those shown in Figures 1-9 and 1-10. Extra custom fixturing for secondaryoperations is very costly and time-consuming. Most parts can be manufactured inone or two set-ups, eliminating the need for extra fixturing and time.

Figure 7-9 Example part requiring positioning multiaxis machining.


Figure 7-7O Part requires two separate set-ups for machining.

AccuracyEvery time you move a workpiece from one fixture to another, there is a riskof misalignment - either during the set-up itself or during operation. It is easyto build up (stacked) errors between machined surfaces when they are milledin multiple set-ups. The use of indexing rotary tables, or dedicated multiaxismachines, as shown in Figures 1-11 and 1-12, al lows precise movement of short ,rigid, high speed cutters for the best cutting engagement. More aggressive cuts canthen be taken, with higher RPM and feed rates, while the highest levels of accuracyare maintained.

Figurc 7-17 Dedicated dual-rotary machine set-up.

History of s-Axis Machines

Figure 7-72 Dedicated dual-rotary machine set-up.

Better Surface FinishesUsing shorter tools wi l l cause less tool def lect ion, which wi l l minimize vibrat ion andproduce smooth, precise, cuts. When using ball-nose cutters it ls recommendedthat the contact point be moved away from the tip of the cutter that isn't spinning.By t i l t ing the tool , as shown in Figures 1-13 and 1-14, the workpiece can beengaged by a desired cutter area, which will not only improve the surface finishand repeatability, but will also greatly improve tool life.

Figures 7-73 and 7-74 Machining parts such as fhese requires simultaneouscuttino motions.

1 0 Secrets of s-Axis Machining

Open New Possibilitiessome parts are impossibre to cut on a 3-axis machine. other parts wourd taketoo many set-ups on a 3-axis machine to be prof i table. Once your shop getscomfortable with indexing work, you wi l l be able to start machining part ; such asthose in Figures 1-15, 1-16, and 1-17, using simurtaneous murt iaxis mot ions, andopen your buslness to many new possibi l i t ies.

Figures 7-75, 7-76, and l-t7 More examples of parts that require simultaneouscutting motions.

A word of caution: Simultaneous mult iaxis work is inevitably Jessaccurate than indexing work because the machine must be run ina loose mode with the rotary drives unlocked. It is recommendedthat al l possible roughing operations be done by indexinq therotaries to optimum angles, because the machine in lockldmode is much more r igid. This type of work is also cal led 2+3machining. The two rotary axes are first positioned and locked intothe optimum attack posit ion, then a standard 3-axis program isexecuted.

11History of s-Axis l\ilachines

Know Your Machine

What do you picture when you see the words "standard s-axis machine?,, lvanyindustry buzzwords are used when descr ibing s-axis machines. Some of theminclude: staggered gulde-ways, constant dynamic control , d igi ta l AC servo motorswith pre-tensioned bal l -screws, permanent posi t ioning monitor ing system, maximumuti l izat ion layout, long-term accuracy, and so on. To simpl i fy th ings, we wi l l say thatthere are three major bui ld ing blocks to these types of machines.

The physical properties of the machineThe physical properties of the machine describe the wav tne axes arestacked, the r ig idi ty and f lexibi l i ty of the i ron, the horsepower, torque,and maximum RPM of the spindle motor, the qual i ty and workmanship ofthe guides/sl ides, and the rotary bear ings.

The CNC drive systemThe dr ive system is the muscles or the components that make themachine sl ides and spindles move. The system includes the servomotors, dr ive system, bal l screws, the way posi t ioning is control led andmonitored, and the rapid-traverse and feed capabi l i t ies.

CNC controller capabilitiesThe control ler is the brain of the machine. Data handl ing, avai lable on-board memory size, and dynamic rotary synchronizat ion controls, aresome of the things control led here.

The perfect combinat ion of the above character ist ics wi l l bui ld a fast , accurate, easy-to-program and operate,s-axis CNC mil l ing machine. lvany manufacturers havespent many years try ing to come up with the perfect combinat ion, and as a resul tthere are manV var iat ions and solut ions.

The l l lustrat ions in Figure 2-1 show some of the var iety that exists in the machinesthat make up the CNC manufactur ing industry.

1 3

Figure 2-7 Typical arrangements of multiaxis CNC machines.

Multiaxis Machine Configurations

The arrangements shown in Figure 2-1 are all very popular configurations, butnone of them is "standard." There is no such thing as a standard S-axis machine.First, let's establish the definition of an axis. Any motion controlled by the NCcontroller, either linear or rotational is considered an axis. For instance, in thei f lustrat ion in Figure 2-2, both the spindle head and the qui l l are capable of movingin the same direction, but are controlled by two separate commands, Movements ofthe head are controlled by Z and those of the quill by W.

Figure 2-2 TheTU

spindle head and the spindle quill move along parallel axes.

1 4 Secrets of s-Axis Machinino

The terms mult iaxis and s-axis are of ten used interchangeably and these termscan be confusing. The widely recognized term in the industry is 5-axis, but i t ismisleading because g-axis standard possibi l i t ies exist - wi thout adding addit ionalsub-systems. In addit ion, a 4-axis machine is also considered to be a mult iaxismachine. Despite the t i t le of th is book, the more accurate term mult iaxis wi l l of tenoe useo.

The fol lowing l ist provides the industry standard nomenclature for the basic g-axisdesig nat ions and direct ions.

XYZ are l inear axes where Z is al igned with the spindle of the machine.

ABC are rotary axes rotating around XyZ respectively.

UVW are parallel linear axes along XyZ respectively.

Know Your Machine 1 5

Unfortunately, different machine builders abide by this standard in different ways.Some builders allow the end user to change the machine's rotational directionsor behavior on the fly. Third-party rotary devices, as shown in Figure 2-3 andelsewhere, can be purchased and mounted on a machine in a variety of ways, Theend result of this flexibility can cause two machines, of the same make and model,to have completely different S-axis behavior.

Every machine is a compromise of some sort. Rotational directions, sta rt positions,and limits, will be different from one machine to another. The effective workenvelope is greatly modified by changing those variables, Some rotary axes canrotate in both directions. Some axes will choose the rotary direction based on theexisting position - shortest distance versus clockwise (CW) or counter-clockwise(CCW). Some machines that are equipped with dynamic rotary fixture offsetmode will move the linear axis while rotating the rotary one based on a rotarycommand.

To understand these machines completely, it is necessary to look at every machineas a unique entity, to look under the skin and understand how the skeleton isconstructed, You need to know where all the joints are, where the rotary axes are,where the rotary zero positions are, what makes them move, and how the wholeunit funct ions in unison.

Different manufacturers and CAD/CAM systems have many different names for thesame things. Let's establish some common terms that will be used in this book inorder to avoid assumptions and confusion.

Machine Home Position (MHP) - Most machinists recognize the home positionas the place to which al l the axes move when you ini t ia l ly turn the machine on andselect Zero return.

Figure 2-3 Machine at Home Position X0. Y0. 20. A0. 80.


Machine Rotary Zero Position (MRZP) - On multiaxis machines, machine rotaryzero shown in Figure 2-4, is at the intersection of the rotary/pivoting axes. Thispoint may be unreachable by the machine.

Figure 2-4 Close-up showing Machine Rotary Zero position.

lrogram Zero Position (PZP) - program Zero position is the part datum in theCAM system.

Figure 2-5 Another view showing the relationship between MachineRotary Zero Position and program Zero position.


When sett ing up/ operat ing/ and programming mult iaxis machines i t is essent ial tomaintain the proper relat ionship between the machine zero posi t ion (MRZp) andthe program zero posi t ion (PZP).

I f the machine does not have special features then the PZP must coincide with theMRZP.

lYult iaxis mi l l ing machines can be organized further into 3 major machine types:

Table/Table multiaxis machines execute the rotary motions by thedual rotary table, The primary rotary table carries the secondaryrotary table, which in turn carries the fixture and the part.

Head/Table multiaxis machines execute the rotary motions by thetable, which carries the work piece, The spindle head articulatesthe tool with tilting motions.

Head/Head multiaxis machines execute all rotary/pivotang motionsby articulating the spindle head of the machine, The work piece isstationary.

Keep in mind that the focus of th is book is mi l l ing, al though the l ine between themil l and the lathe is blurr ing more and more every year. There is a new breed ofmult i - tasking machines avai lable that can do mi l l ing and turning, and those arecal led Mi l l /Turn machines.

For the sake of s impl ic i ty, we wi l l focus only on mult iaxis mi l l ing machines.

Table/Table Mul t iax is Mi l l ing Machines

Table/Table mult iaxis mi l l ing machines can be veft ical or hor izontal . Al l therotary mot ions except the spindle are done by the tables of these machines. Themain rotary table carr ies a second rotary table, as shown in Figure 2-6, to which isfastened the f ixture and the Dart to be machined.

Tool length of fsets work the same way here as with anv convent ional 3-axismachine. The tool length can be changed without the need to re-post the NC data.

On these machines, the part is physical ly rotated around the tool . The machine'srotary devices need to be capable of handl ing the weight of the part and thef ixture, and this capabi i i ty is an impodant factor when rapid movements areconsidered. Another var iat ion is seen in Figure 2-7.

The examples shown represent only a smal l f ract ion of the avai lable Table/Tablevar iat ions. Most of these machines have minimum and maximum rotarv l imits on


one of the rotary axes. some will have unlimited rota ry motion on the other axis.Some even have the capability to spin the work, as a lithe woutd.

Table/Table machines are the most common types of murtiaxis machines. Mostpeople will enter the s-axis world by purchasing-a single- or dual-rotary device andbolt i t to their 3-axis mil l ing machine

Figure 2-6 Simulation of a dual rotary mechanism fastened to the tabte of astandard 3-axis CNC milting machine.

Figure 2-7 A third-party rotary mechanism fastened to the tabte of a standard3-axis CNC milling machine.


Figure 2-8 Third-pafty single rotary mechanism and tailstock, fastened to thetable of a standard 3-axis CNC milling machine.

After machining one side of the work piece it is possible to index the rotary unitto machine the second side, and so on. This type of work is called indexing orpositioning work. Some manufacturers use specialized dual rotary mechanisms.such as the one shown in Figure 2-9, which is designed for machining internalcombust ion engine components.

Figure 2-9 Specialized dual rotary mechanism used in engine manufacture.

20 Secrets of s-Axis Machining

Dedicated Table/Table machines are very capable of doing indexing/posi t ion ingwork and are equarry capabre of s imurtaneous work. The inherent di f lerencesbetween the two are worth ment ioning.

The rndexing method hords the workpiece much more r ig idry than i t is herd forsimultaneous machining work because the rotary axes are-rocked when machining.when rotat ing an axis, the rotary axis must f i rs l be unrocked with a designateJ

-

M-code. The axis is then rotated, and i t is rocked with another M-Code b-eforemachining is resumed. This sequence al lows machining to be done in the machine,smost r ig id state.

when using simurtaneous mi| | ing techniques, aI the brakes must be disengaged,which wi l l put the machine in i ts roose mode. For this reason i t is arways u g-ooiidea to use (when possible) indexing/posi t ion ing mi l l ing techniques foi roujhingcuts.

Machine Rotary Zero position (MRZp)

Commonly, MRZP represents the intersection point of the rwo rorary axes,although sometimes the two rotaries may be offset by a specific disfance. Thisdistance must coincide or be relat ive to the part datum pZp (program ZeroPoint) of the CAM system.

To accurately set up, operate, and program these machines, i t is necessary tof ind the intersect ion of the rotary centers of the machine axes. some. but not al i ,manufacturers have the varues stamped on their rotary devices. However, thosenumbers are not to be trusted, and must be recal ibrated regular ly.

Finding the precise center of rotat ion is the foundat ion ofaccurate work.

Even smal l d iscrepancies wi l l magnify errors. further away from this machine rotaryzero point .

Know Your l\.4achine 21

Here are the steps to be taken:

1. Level the table by "zeroing" the indicator on either side of the table, asshown in Figures 2-1O and 2-11

Figures 2-7O and 2-77 Method of checking the level by dial-indicating both sidesof the workholding table

Figure 2-72 Setting the dial indicator to zero before checking the level of thetable.


2. Find the XY zero, using the dial indicator, Zero xy and A at this point, asshown in Figure 2-13,

Figure 2-73 Zeroing XY and A positions on the work-holding table.

3. Rotate A+9O degrees and touch the OD of the table as shown in Flgure2-t4,

Figure 2-74 After rotating the A axis through 90 degrees, touch the outsidediameter of the table with the dial indicator.

Know Your Machine

4. Rotate A-axis through 18O degrees from the previous position and makesure the indicator reads zero on the other side.

Figure 2-75 After rotating the A axis through -90 degrees, touch the outsidediameter of the table with the dial indicator'

5. Move the Z-axis in minus direction the radius of the rotary table and setup a gage tower. The gage tower is used to set all the tool length offsetsto z=o.

Figure 2-76 A gage tower is built to represent the MRZP to allow tool lengthoffsets to be set.


This location is the machine's rotary zero position (MRzp), as illustrated inFigure 2-17,

outlined procedure.

Note that the intersection of the dual rotary center lines is above the table inthe example given. This location will be different for every machine, even fromthe same manufacturer. It is imperative that this position be checked regularry,especial ly af ter a heavy workload or a crash, Smal l misal ignments can cause iarqeerrors because the tool position is measured from this intersection point.

All the Active coordinate systems also referred to as Nesting positions orLocaf Coordinate Systems, for example G54 - Sg, are relative to the MachineRotary zero Point (MRZP) position. It is good practice to set one of the nestingpositions here, so that it will be captured in the Registry allowing it to be recalle-dquickly, using MDI (Manual Data Input) .

Fo r examp le : c90 c54 x0 . y0 . A0 . c0 .

Figure 2-77 The rotary zero position of the machine, as established by the

The PZP (Program Zero point) of the CAM systems must be set exac vto the Machine Rotary Zero point, as seen in Fiqure 2-19.

Know Your Machine

Figure 2-78 Relationship between the MRZP and the PZP.

Some CAM systems call this position the World Zero, Master Zero, or the Origin.The main thing to remember is to draw the part in the same specific positionrelative to this World Zero as it sits on the machine, relative to Machine RotaryZero Point.

Nesting Positions

Nesting positions are widely used for positioning work. These positions, shown inFigure 2-19, are temporary Active Coordinate Systems and are typically set inrelation to different faces of the part or fixture face, tooling ball, or dowel pin.

Figure 2-19 Sketch showing some ofthe many local coordinate systems used inCNC programming.


The advantage of using these Locar.coordinate systems is that you can easiryfol low the program on the control ler ,s display sc.een because the absojutevalues shown there will reflect the values relative to each locally-nested position.Z+1.000, for example wi l l be 1.000 ( inch) above the part face.

Despite the fact that cAM systems a

use different naming conventions for theircoordinate systems/ they alr handre the rocar coordinate system in a simirar way.Some.of the names used by_ CAD/CAM systems include: p'art Datum, ActiveCoordinate System, Local Coordinate System, System View, and Tool planewith an Origin.

The disadvantage of using a number of different rocar coordinate systems is thepotent iar for misar ignment when picking up these posi t ions manuairy with a dialindicator. Many programmers us_e only _one coordinate system for S_axis wort<. itreyusethe Machane Rotary zero point (MRzp) as the pirt datum and ret either thecAN4 system or the machine's controler carcurate the speciar rou"r"nt. nui"iruiy.I f a part is placed in the same posi t ion in the cAM and in the machine, the ciM i ; 'very capable of generating the correct code.

The advantage of using a singre coordinate system is that the part needs to beindicated only once. The disadvantage is that i t is harder to v isual lv fo l low theprogram on the controller's display screen. The system will have to be switchedover to Distance to Go for safer operation.

using a real s-axis machine as a verification system is inefficient, cumbersome,and very dangerous. There are many machine simulat ion softwaie t ; .k;&;

- '

avai lable that can save a rot of t ime and money, and these are covered in anotherch a Dte r.

Rotary Table Dynamic Fixture OffsetThe ProblemcAM generates,code for a given position of the program zero point (pzp) rerativeto the center of rotation machine zero point, (MRZF). The machine operito,. maylun th: c.ogg later, on the night shift, at a different tocation ApZp (Actual partZero Point). He or she may not be able to place the part exacfly where the CAD/cAM programmer intended it to be. If the operator does not have the access or tireability to make the change, then the job wiri have to wait for a reposted code to besuppl ied.

Modern CAD/CAM systems can easily calculate new code if the part is moved.But as previously mentioned, the part will have to be moved to exacfly the sameposition in the cAM system and then the code wil have to be recarcurited.

The SolutionIf the operator doesn't have access to the cAM system/ and is unable to matchthe cAl4's part position on the machine, an option on the machine wi[ be neededto compensate for the discrepancy between the two posi t ions. This opt ion is cal led

Know Your l\y'achine

Rotary Table Dynamic Fixture Offset (RTDFO).

When the Rotary Table Dynamic Fixture Offset function is activated on thecontroller, the Program Zero Point (CAM datum) is offset to correspondwith the set fixture offset amount, as shown in Figure 2-20. This offset is thedistance between the center of rotation (MRZP) and the Part Zero Point (PZP)and it must also take into account the angle of the rotary table. This function isconvenient because multiple-face machining can be executed by setting one pointas the reference when machining a complex workpiece.

Figure 2-2O Potential problems in establishing the rotary table dynamic fixtureoffset (RTDFO).

There are 2 wavs to use RTDFO:

1. Set the fixture offset amount manually on the Fixture Offset screen ofthe machine, illustrated in Figure 2-21,


E-1grylo1selection rey E (oFFSET)--+ IFIXTURE OFFSETI

Figure 2-21 A Fixture Offset Screen on a CNC machine.

2. Speci fy the values in the machining program (G-Code).

The fixture offset amount is the distance between the rotationai center (MRZp)and the workpiece zero point, used by the CAM program as the program Zero(PzP).

GlO L21 Pn X_Y_Z_B_C_

n Fixture offset number (1_g)

X_Y_Z_B_C_ Fixture offset amount for each axis

When using the c90

When using the G91set.

mode/ the speci f ied values are set.

mode, the sums of the speci f ied and the previous values are

Know Your lvlachine 29

Act ivat ino RTDFO:

G54,2 Pn; RTDFO - ON

G54,2 PO, RTDFO - OFF

n Fixture offset number (1-8)

The G-Code below shows an examDle:

00001 { P,ROGT?Ar, - ZERO )( D]TE A2 ] i A7 T INE 07:22 )

G21c0 G17 G40 cac c90 G94 G9a

I rooL 3) D.aa. oii. - 3.1 ,,rN_ 3) Dra.( G13.4 G5 P l0O00 )

T3tM6

c 9 0 G o 2 5 0 0 . s 0 . c o _c 4 3 . 4 ! 3 1 2 2 s 0 .

G 5 4

M69

c 9 0 G 0 x 1 3 ? . 0 4 3 y 3 . 5 3 ? C - 3 1 . 2 6 6 8 1 8 . 0 0 1 S t ' t t a t t \ 1 3

293.4 , -1G 1 5 3 3 . 4 r 7 F : ' : r 0 . . ., 1 3 5 . 3 4 6 y 3 . 2 5 3 2 8 3 , ? ? 6 C 3 1 . 6 4 A 1 3 . 2 0 9 F ; 0 0 D ." < t 3 4 . 6 3 9 v 2 , 9 2 3 ? 8 9 - 0 3 ? C - € 1 . 9 9 ? 8 1 9 , 3 2 4x 1 3 3 . 4 6 4 y 2 . 5 2 6 2 8 9 . : , ! 4 C - 8 2 . 3 3 1 8 1 8 . 4 1 3x t 3 2 . 3 2 1 1 2 . 0 6 1 2 3 9 - 3 3 5 c 3 2 - 6 3 9 B l a . 4 t 6x l 3 0 . 9 8 3 y l . 6 0 5 2 3 9 . ? 3 4 C 3 2 - 9 4 6 8 1 8 . 6 5 2r 1 , 2 9 . 4 6 y 1 - 3 8 2 2 9 0 . 4 2 4 c 8 3 . 3 3 5 8 1 6 . 9 3 4x ! 2 ) . 1 2 2 y 7 , 5 4 ? 9 1 , 3 2 4 C - 8 3 , 8 6 9 3 1 9 . 3 1 6x 1 2 5 . t 3 8 y 2 . 1 9 6 ! 9 2 - 5 0 4 C - ! 4 . 5 9 1 B 1 9 , € ? 4x 1 2 4 . 0 6 ? y 3 . 4 2 1 2 9 3 , 4 9 2 C - E 5 - 4 3 9 B 2 0 . 3 3 4

00001 { P.eoGr?Ai, - cLoNE2 )( DA?a - O2- i1 -07 T IME - A7:22 )

G 0 c 1 7 G 4 0 G 8 0 G 9 0 c 9 4 G 9 8

c 2 8 X O . Y O , B O ,

( laoL 31 Dra . a !F . 3 :L LEN- 31( c43.1 G5 P1A0O0 )

T3tM6

0 9 0 6 0 2 s 0 0 . B 0 . c 0 .c 4 3 , 4 f l 3 1 2 2 5 0 .G05 P10000G54

M69

G 9 0 G 0 x l 3 7 . 0 S 3 v 3 . 5 3 7 c - e l . 2 6 6 8 1 E . 0 8 1 s L 0 a i : ; a r ' 1 32 1 8 8 , 4 ? l29 ' . j . 411G t 2 4 4 . 4 7 1 ? 2 n 1 4 .x 1 3 5 . 8 4 6 y 3 . 2 5 8 Z A 3 . ? ? 5 C 4 1 . 6 4 8 1 4 . 2 0 9 F r i 0 t r C _x , L 3 4 , 6 3 9 y 2 . 9 2 3 2 8 ! . 0 3 ? C - e 1 , 9 9 7 B 1 8 , 3 2 3t t 3 3 . 4 6 4 v 2 - 5 2 6 2 a 9 . 2 4 4 C - 3 2 . 3 3 1 B 1 8 . 4 ! 3x l 3 2 . 3 2 1 y 2 . 0 6 1 z A 9 . i 3 s c 3 ? . 6 3 9 B 1 3 . 4 7 6x 1 3 0 . 9 8 3 y 1 . 6 0 6 Z A 9 . ? 3 3 C 8 2 . 9 4 6 B 1 3 . 6 5 2. A 1 2 9 . 4 6 1 7 , 3 4 2 2 9 0 . 4 2 4 C - 8 3 . 3 1 5 8 1 8 . 9 3 4x t 2 1 . 7 2 2 r 1 . 5 4 2 9 1 , : 2 4 C - 8 3 . 8 6 9 8 1 9 . 3 1 .t L 2 a . 7 3 a v 2 . 7 9 6 2 9 2 , 5 0 4 C - S 1 , 5 9 1 B 1 9 , 8 7 4t r 2 4 . 0 6 1 v 3 - 4 2 1 2 9 t . 4 9 2 C - 4 5 . 4 3 9 8 2 4 . 3 3 4

Figure 2-22 Example of G-Code data for setting RTDFO.

If the machine does not have the opt ion ment ioned above, the CAD geometry wi l lhave to be moved, and the G-Code re-posted in the CAM system.

Note that the above examDle is for Fanuc control lers. Other control lers have avar iety of names for th is and simi lar funct ions.


Head/Table Mul t iax is Mi l l ing Machines

As their name suggests, these machines have a rotary table and a t i l t ing head.

Figures 2-23, 2-24, and 2-25 Example of Head/Table multiaxis milling machines,which have rotary tables and tilting spindle heads.


Head/Table machines are arguably the most capable of the three groupsi l lustrated and can machine large, heavy parts. On some machines, the rotarv tablecan be supported by a steady rest and it rotates the paft only around its own axis.The pivot ing spindle head carr ies the weight of the tool . I t needs to be capable ofhandl ing the cutt ing pressures as i t is manipulat ing the tool .

These machines are also wel l sui ted for both indexing and simultaneous work.Some have the capabi l i ty to calculate axis subst i tut ion internal ly, enabl ing the userto program parts in the 2D f lat plane and then wrap the plane around a speci f iedfou rth -axis diameter,

How does axis substitution work?

Axis substitution is shown in Figure 2-26, and is effected by the followingoroced u re.

lYeasure the A-axis diameter and mult ip ly i t by pi to f ind the circumference.Draw a rectangle where the Y side is the circumference and the X side is thelength of the part .Create the cutt ing geometry inside this rectangle.Create a 3-axis toolpath, XYZ, and activate axis substitution by first definingthe A-axis diameter.

On a Bostomatic control ler , for example, th is resul t is achieved by adding two l inesof code.

G25 A3.OOO A-axis diameter

G131 Axis substitution Y to A active

Figure 2-26 A part produced by means of axis substitution.

After these blocks are read, all Y-axis moves will be replaced by instructions forA-axis rotary mot ions. I f the machine doesn' t have this capabi l i ty, th is sameprocess can be achieved with any modern CAD/CAM system.

The rotary axes on these machines usual ly have unl imited rotary mot ion. Somemachines can even spin the workpiece as in a lathe. The secondary pivot ing axishas an upper and lower l imit . In order to accurately set up, operate, and program


these machines, it is necessary to find the intersection of the rotary and thepivoting axes. Some examples of machines at the Zero position are shown inFigures 2-27, 2-28, and 2-29

Figures 2-27, 2-28, and 2-29 Examples of machines with spindles at the zeroDosition,

Note that wi thout consider ing the tool , a l l these machines al ign the spindle facewith the center of the rotary axis while the pivoting center point is some distanceaway from center. This distance is commonly called the Pivot Distance. The GageLength is the distance from the spindle face to the tool tip.

The sum of the Pivot Distance and the Gage Length is the Rotary Tool controlPoint (RTCP), which has to be triangulated for every s-axis position of thetoolpath. Figures 2-30 and 2-31 show examples of B90 rotation with and withoutRTCP.

Figure 2-3O Example of 890 rotation without RTCP, and Figure 2-37 890 withRTCP active.

Know Your Machine

The machine's l inear axes also have to move along the X and Z axes in order tokeep the tool tip stationary in space as it executes the pivoting B90 motion. CAMsystems wi l l make the necessary calculat ions dur ing "post processing., ,Somemachines have the abi l i ty to calculate the necessary mot ions automatical ly, basedon the of fsets shown in Figure 2-31, captured in the machine control ler ,s reqistr ies.

PIVOT

rbor- rr'rerrt

Figure 2-32 Multiaxis offsets.

Fanuc examole:G43.4, G43,5 s-AXIS ROTARY TOOL CENTER POINT CONTROT (RTCP)

If the Rotary Tool Control Point (RTCP) function is used in the Fanucprogram, the spindle position is automatically adjusted in synchrony withall rotations, as shown in Figure 2-33 and the listed code lines beneath thefigure. As a result, the relationship between the tool center point and theworkpiece will always stay fixed.

TANCE =

COMP OFFSET

34 Secrets of 5-Axis lvlachining

Prog.am- Specifed

between the tool center point and the workpiecestav constant,

G90 G54 c00 x0 Y0 B0 co t

S-MO3 ;

G00 G43 .4 Z_H_ ;

X_Y_B_C_ t

G49 ;

G43.4 . . . Tool center point function (Type 1) ON

x, l ,z, . . . (G90) The coordinate value of the end point of the toolcenter movement

(G91) The travel amount of the tool center

B,C . . (G90) The coordinate value of the rotary axes end point

(G91) The travel amount of the rotary axes

H . . . Tool length offset number

c49 . . Tool center point control function (Type 1) OFF

Example:

G 9 0 G 0 0 G 5 4 x 0 , Y 0 . 8 0 . C 0 . ; . M o v e s X , t , B , C t o P z P

s 5 0 0 0 M 0 3

G43 . 4 zL . H01 ; . Activate RTCP. Positions the tool tip at Z+ 1.000while Z axis position is offset by offset data set for tool lengthoffset number 1.


Some Head/Table machines will use both RTCP (Rotary Tool Control Point)and RTDFO (Rotary Tool Dynamic Fixture Offset) simultaneously. While RTCP isoffsetting the tool position a combined distance from the head's rotary point (pivotdistance + gage length), RPCP is compensating for the relative distance of the partfrom the MRZP (Machine Rotary Zero Point) to the actual fixture position.

If the machine doesn't have RTCP, to avoid repeated re-posting when toolsare changed, it is common practice to pre-set all tools to the same length whenDossible.

Head/Head Mult iaxis Mi l l ing Machines

All the rotary/pivotino motions are executed by the spindle head of the machine.These machines can be both vertical and horizontal, and they have limitedmotion. Some machines can change heads, not just tools. Heads can be straight,g0-degree, nutat ing, or cont inuously indexing. Some examples are shown in Figurez- 5+ .

Figure 2-34 Examples of Head/Head machines.


All Head/Head machines have di f ferent behavior; based on indlv idual instal lat ionsett ings. Rotary direct ions, l imits, retract ions, rotary wind-up, and handl ingsingularities can all be altered from factory settings. The most impoftant basicdimension needed is the rotary/pivot center pointr which is measured from thespindle face to the head's rotary posi t ion. Machine manufacturers sometimesprovide a nominal value, but i t is essent ial that the manufacturer 's value bedouble-checked/ especial ly i f i t is a nice round number, for instance, 10 inches. Theroundness is a good lndicat ion that the number is not accurate.

"Close" is not good enough. Knowing the exact dimensionis vital if precision work is to be done.


1. First , make sure that the machine head is in a perfect vert ical or ientat ion bytouching the machine's table with a dial indicatol then rotat ing the indicator.The indicator should read zero around the whole circ le as shown in Fioure2 -35 .

Figure 2-35 Indicating vertical position.

2, Place a 1.000 diameter dowel pin into the master tool holder with a knownGage Length (GL).

3. Touch the dial indicator plunger as shown in Figure 2-36. A f lat at tachmenthelps here. Set the indicator to zero and record the Z value on the control ler 'sscreen. Let 's cal l th is value Z maximum.

Know Your l\,4achine 37

Figure 2-36 Touching the dial indicator plunger is eased by having a wide, flattop on the plunger.

Do not move the machine on the X axis. Move only on the Y and Z axes. Moveto a safe point on the Z axis, and rotate the A axis through 90 degrees into ahorizontal orientation. Next, move on the Y axis in the plus and on the Z axisin the minus direct ions unt i l you get to the posi t ion shown in Figure 2-37.

Record this Z value on vour control ler 's screen and let 's cal l th is Z minimum.

Figure 2-37 Z minimum position.


You should have the fol lowing values handy:

Z maximum

Z minimum

GL - Gage Length

R - Dowel pin radius = .5OOO

Formula to calculate Pivot Distance:

P D = Z m a x - Z m i n - G L + R

This distance (PD). will be used by the post processor. Most CAM systems willdrive the Pivot Point and they will have to calculate the tool tip location for everyprogrammed position. The tool tip location is the Pivot Distance plus the GageLength away from the Pivot Point at all times, and must be triangulated based onthe rotary/pivoting angles. Even small discrepancies in the Pivot Distance will bemagnif ied into large tool posi t ion errors in the f inal program.

4-Axis Machines

I f a third-pafty, s ingle rota ry mechanism is placed on a 3-axis mi l l ing machine, i tbecomes a 4-axis machine. The most oopular dedicated 4-axis machines are thehorizontal types shown in Figure 2-38.

Figure 2-38 4-axis horizontal machining center.

Know Your Machine

These machines are most ly used for tombstone work, where parts are clampedto all sides of the tombstone fixture and machined by rotating them into differentposi t ions, The chips don' t col lect on the work-piece because they fal l away bygravity and are cleaned off by strateg ica lly-placed coolant nozzles.

The example in Figure 2-38 shows a pal let changer, which is posi t ioned outside themachine's enclosure, al lowing the operator to load workpieces and unload f in ishedparts dur ing the machine cycle. Elaborate pal let changer assembl ies are alsoavai lable, wi th mult ip le tombstones on which a var iety of di f ferent jobs can be pre-loaded and made ready-to-run. This arrangement al lows for quick changeover to anew job without stopping the machine.

General Maintenance and Issues for Multiaxis Machines

I t is recommended that al l machine tools be kept c lean and free of objects thatcan cause damage, and this rule is even more important on s-axis equipment.Real igning rout ines should be done at regular t ime intervals, and most certainlyafter heavy work, over loads, or a crash, A log should be kept of the machine's v i ta lstat ist ics and operators should be instructed to l isten for any new sounds comingfrom the spindle(s) or rotary mechanisms.

Some common oroblems include:

. Sometimes the rotary brakes will fail and they won't disengage, The rotarymechanism will then work extra hard to rotate from position to position, and ifs imultaneous work is in hand, the uni t wi l l eventual ly fa i l .

. Some dual rotary table center l ines do not intersect. Some of these apparentdiscrepancies are by design, as shown in Figure 2-39, and some are not. I f theapparent error is by design, i t is usual ly a large number that can be seen byeye. I f i t is not by design, i t won' t be not iceable. I t must not be assumed thatthe center l ines are in l ine, and they must be checked, Misal ignment can becompensated for by inputting the relevant value into the post processor,

Figure 2-39 Example of rotary mechanisms placed in offset positions by design.

40 Secrets of 5-Axis l\4achinino

Figure 2-4O These rotary mechanisms appear to be intersecting.

Some Head/Head types of machines will not run true. To check this aspect,arrange the machine with the secondary axis pointing down vertically as shownin Figure 2-41. Then, rotate the primary axis through 360 degrees. The dialindicator should read zero throuqhout this motion.

Know Your Machine 41

Figure 2-47 Indicating run-out.

The machine types described in this chapter are built by many different machinebuilders in a variety of sizes, shapes, qualities, and prices. The quality of a machinewi l l be best highl ighted when fast. s imultaneous, mult iaxis mot ion is being used.A good-quality machine will execute these motions quickly and repeatedly, in asmooth synchronized way, without one rotary axis waiting for anothel and withoutbacklash or v ibrat ion. The rotary mechanisms wi l l have minimal run-out, and therotary centerlines will align precisely. Cheaper machines may execute positioningmovements wel l , but wi l l execute simultaneous mot ions poorly.

Many manufacturers will list "positional repeatability" in their specifications becauseit is a good measure of the machine's quality. One way to do a quick check ofrepeatabi l i ty is to set up an indicator on the machine table, engaging the tool holderat zero. Then a ten-minute rout ine involving al l the machine axes with mult ip lerotational moves should be executed, terminating with returning to the startDosition. The indicator's readout retative to zero is the measurement of the Dositionalrepeatability.

It is not necessary to buy the most expensive machine, but only to take a goodlook at current and potential future needs when considering purchase of a multiaxismachine.


Milling Machines with Five or More Axes

lVost machines with more than five axes are built for specific manufacturingapplications, Some examples include those shown in Fioure 2-42:

Figure 2-42 Some examples of more than s-axis machine designs,

It is possible to assemble multiple 9-axis subsystems, and some manufacturershave built machines with over 100 axes. Many of these axes are part of elaboratework-holding systems, and have parts that need to be rotated out of the wavof other machine components during some manufacturing processes. Manysuch machines are controlled with dedicated M-codes, which activate pre-setsubroutines.

Know Your Machine

EA simple example of such a subrout ine is an M06, which causes a tool change.Observe closely what happens on any machine with an automatic tool-changer:the machine slides travel to pre-determined locations; the tool-change carouseladvances the chosen tool; a little trap door may open, depending on themachine; then a swing-arm wi l l exchange the tool between the spindle and thecarousel. This whole choreography is just one of many internal macros, readyto be activated by a simple code like M06. On multiaxis machines, many more ofthese internal macros are available. Most of the time, the macros need to work insvnchronization,


Cutting Strategies

I f drawings of the same mult iaxis part were given to f ive different CNCprogrammers, chances are good that they would come up with f ive differentmethods to machine the part. This variabi l i ty is a product of experience, availablemult iaxis equipment, available CAD/CA[4 systems, tool ing, f ixturing, material, andquantit ies.

What does every CNC programmer do when asked to write a program for a newpart? He or she wil l create a mental image of the part, and based on the abovefactors, go through a variety of different scenarios to determine how to machineit. These decisions wil l include how to hold the part, and which side to start on.The programmer wil l then mental ly go through the whole process of removing al lthe excess material from the starting stock in order to free the desired part fromwithin i t . Most programmers wil l brainstorm repeatedly and come up with mult iplesolutions, el iminating the weakest ones, adding new ideas, and then making thefinal decision. This whole process happens long before the creation of the actualtoolpath. This pre-work meditation is the single most important part of the wholemanufacturing process.

The process described above is the same, whether 3-axis or mult iaxis work isbeing considered. The big difference is usually with the f ixturing. Work holding isamong the f irst decisions to be made when programming a 3-axis machine. Manymult iaxis programmers wil l place the part data on a virtual machine. This processlets them levitate the part in the air and simulate the machine's motions, withouta f ixture present, to see if al l motions are possible without violating the machine'swork envelope boundaries. The part wil l be moved in space to achieve optimized,synchronized motions. Final f ixture placement, or design, might be one of the laststeps,

Of course this procedure is not always possible, but when a f ixture ispredetermined, addit ional effort wil l be needed to make sure there are no coll isionsbetween the f ixture, tool, shank, arbor, or tool holder. Avoiding coll isions is a bigpart of mult iaxis programming. Coll isions can occur not only during cutt ing, butalso during tool changes, pallet changes, or manual retraction moves after anabrupt program stop. For example, after a power fai lure, the tool could be in aposit ion where the onlV safe retraction move is simultaneous mult iaxis motions.

The single most important part of mu t iaxis programming is the init ial t ime thatis spent on deciding how to tackle the job. I\4achining sequences should be keptsimple, not made complicated just because the shop has the latest equipment, themost powerfu CAD/CA[4 system, or an unlimited budget. Here are some questionsthat need to be considered:

How many parts are needed?

How much t ime is available?

what is the material?

What machine is available?

How good is the CAD/CAM system?

How well do you know CAD/CAM?

what tool ing is available?

Do you have to use exist ing f ixtures or can you make your own?

Ar€ there any special requir€ments?

Limitations apply to every too in the shop. The tr ick is to work around thoselimitations. The difference between a good mult iaxis programmer and an averageone is that the good one is industrious. If one approach doesn't work, another onewil l be tr ied Lrnti l the best solLrt ion appears. Regardless of the CAD/CA|4 system inuse, many t imes extra geometry wi I have to be created to achieve the best resu ts.

Do the Prep WorkThe t ime invested in preparing the work wil l be invaluabLe in the ong run. once adecision has been made on how the job wil be handled, i t is important to organizethe work. Divide up the operations in the CAD/CAM system and move necessarygeometry to easily-recognizable named layers/levels. This preparation wil l make itpossible to isolate individLral features and al low a focused workflow.

Make a Tool ListIt is very important to make a tool l ist for any job. Start by analyzing the partgeometry di l igently. Find the smallest f i l lets. Measure how much room there isbetween features to determine the minimum and maximum too diameters that canbe used. Check what tools are readiy available in the shop to see if any of themcan be used, especial ly i f you are a ready famil iar with their performance. If youmust order tools, do some research on their performance and availabi l i ty.

46 Secrels of 5 Axis Machining

Determine FixturingCheck on available f ixtures, vises, and clamps. Use exist ing vises and f ixtureswhenever possible, to keep the costs down. The equipment should be modeled inthe CAD/CAM system and organized into l ibraries that can be readily accessed andloaded for virtual simulation when checks are made for possible col l isions.

Compare MachinesI f more than one machine is available for the job, some comparisons should bemade. Among essential checks are: work envelope l imitations, maximum RPIY,feed-rates, and control ler capabil i t ies.

Know Your Stock Optionsl '4aterial stocks must also be considered. If the material is unfamil iar, someresearch wil l be needed on different cutt ing characterist ics. The original form maybe a bi l let, a cyl inder, a casting, or a forging, and may require some preparatorywork before machining can start.

Cutting Strategies

Indexing Multiaxis Toolpaths

Set-ups using indexing or indexed work are rigid and precise. Other common namesused for such set-ups are 2+3 machining or positioning, and fixed rotary work. Withindexing work, the rotary/pivoting axes are used only for positioning, and cutting(machining) takes place with only the three l inear axes moving, Indexing work isthe "bread and butter" of the multiaxis machining industry. Many parts are mass-produced by this method, and it is the most basic multiaxis concept. It is an easytransition from multiple set-up, 3-axis work to a single set-up indexing one, Thegraphics in Figure 4-1 show how one part can be cut from many different angleswithout being removed from the fixture.

Figure 4-7 Images showing how one part can be cut from many different angles,without being removed from the fixture.

49

Figure 4-7a Images showing how one part can be cut from many different angles,without being removed from the fixture.

Figure 4-2 Part of an aircraft landing gear machinedwith an indexing set-up.


The concept may be simple, but it allows for the manufacture of very complexparts with precision, like the samples shown in Figures 4-2 and 4-3.

Figure 4-3 An aerospace component machined with an indexing set up.

Indexing Methods

There are many different indexing methods, and they can pedormed withequipment as simple as a manually-operated, custom indexing fixture. Third-partyautonomous rotary devices also are available, which will execute pre-programmedindexing sequences at every cycle. The cycles can be activated manually or througha dedicated M-Code. If one of these methods is used, great care must be taken tosynchronize the manual operations with the Nc-code, Ample opportunities exist tomake a mistake with these methods.

Figures 4-4 and 4-5 show two examples of custom indexing fixtures.

Figures 4-4 and 4-5 Two examples of custom-built, indexing fixtures.

Indexing Multiaxis Toolpaths 5'l

The best method is to use fully-integ rated. third-party, rotary devices, which willexecute rotary commands directly from the Nc-code. For these methods, the rotarypivot center must be precisely located (as described in Chapter 2).

Figures 4-6 and 4-7 show some examples of dedicated third-party rotarymechanisms.

Figures 4-6 and 4-7 Examples of dedicated third-pafty rotary mechanisms.

The best approach is to use a dedicated mult iaxis machine, i f one is avai lable.These machines have brakes on their rotary/pivoting axes, which provide extrarigidity during cutting. Typically. these brakes are released while positioningchanges are made, but once in posi t ion, they are re-engaged so that the machinecan stay in its most rigid state for cutting. Some machines are not numericallycontrol led but are capable of indexing only in certain increments ( for example,1 degree), and they often operate by lifting away from a serrated dividing plateduring indexing.

52 Secrets of s-Axis Machinino

Figures 4-8 and 4-9 show some examples of dedicated multiaxis machine, rotarymechanisms.

Figures 4-8 and 4-9 Some examples of dedicated rotary machine components.

On some machines, spindle heads can be changed repeatedly between operations.The examples shown in Figure 4-10 can be straight, set at a specific angle, or evenadjusted steplessly to various angles.

Figure 4-7O Spindle heads on some machines are designed to be straight, set at aspecific angle, or even adjusted steplessly to various angles.


Other machines, used mainly in the medical and aerospace industr ies, are designedto index and hold the part wi th gr ipping axes whi le machining. Examples of thesetypes of machines are shown in Figures 4-LL and 4-I2.

Figures 4-77 and 4-12 Some machines are designed to index and hold the partduring machining.

Plain indexing is a very efficient way of moving parts into position for machining,especial ly when i t is combined with pal let-cha nging. A pal let changer can beas simple as a single rotary indexing mechanism. I t can also be as complex asa mult i -pal let conveyer, wi th not just one, but mult ip le jobs, running in a pre-organized sequence. These systems are so flexible that a brand new job can beintroduced into the queue without stopping the machine sequence, as shown by theexamples in Figures 4-L3 and 4-L4.


Figures 4-73 and 4-74 Brand new jobs can be introduced into the queue withoutstopping the sequence with these pallet-changing machine designs.


How CAD/CAM Systems Handle Indexing Work

Before discussing CAD/CAM system applications, it is important to establish somecore understanding of how CNC machines work.

Prior to the invention of CAD/CAM systems, G-Code needed to be generated "by

hand." Indexing work was handled just l ike any other programming job, the onlydifference being that another one or two axes were sometimes added to the mix.Most machine controllers have the ability to work in multiple local coordinatesystems, also known as nesting positions. These local coordinate systems were,and st i l l are, used in a var iety of ways, One of the simplest ways is to place mult ip lefixtures and parts on the machine, establish the part data for each individual paft,and assign indiv idual local coordinate systems, as shown in Figure 4-15.

Figure 4-75 Positioning two fixtures with parts on a machine and assigningindividual local coordinate systems.

The above example shows only two positions. The part programs would be the samefor both, except that the local coordinate system designation would be providedat the beginning of the NC program (for example, G54 or G55 Fanuc). Differentcontrollers use different designations for these nesting positions, but they all work onthe same principle. Depending on the controller, numerous nesting positions can bedesignated,

This nesting concept is one that many people struggle with, and its understandingis key to multiaxis machining and programming practices. There are a variety ofcontrollers and machines available that use this same concept, but they use differentterminology to describe it,

tz


Machine Coordinate Systems

Machine Home Posi t ion

Simply put, Machine Home Posi t ion is the center of the machine's universe.Every axis wi l l t ravel to i ts Home (end of t ravel) posi t ion and the machine wi l l stopthere. At th is Home posi t ion, in the machine's Absolute Coordinate System, al laxes are read ing/d isplaying zero. Every move the machine axes make from herewi l l be relat ive to this zero. Every posi t ion captured, such as a nest ing posi t ion,wi l l be a relat ive posi t ion in the Machine Coordinate System. Every t ime a toolis changed, the machine wi l l go to the pre-determined posi t ion speci f ied in thisMachine Coordinate System.

To establ ish the nest ing posi t ions, the f i rst v ise is loaded and checked to makesure i t is square and secure before i t is c lamped in posi t ion. Then the workpiece isplaced in the vise and the vise is t ightened to hold the workpiece in place. Usingan edge f inder, the center top of the part is located, as shown in Figure 4-15. Themachine's absolute posi t ion display should now show how far the axes are fromthe Home posi t ion. This posi t ion must now be captured and the machine mustbe made to remember this locat ion. Machines remember by stor ing the relat ivedistances ( f rom Home) in their registry. How nest ing posi t lons are'captured'depends on the type of machine and control ler in use.

Active Coordinate System

Nest ing posi t ions on a mult iaxis machine can be moved and rotated in one plane.They can also be rotated about the machine's rotary/pivot ing axes.

The Machine Home Position is the center of the machine's universe.

Indexing Multiaxis Toolpaths 57

Figure 4-76 Multiple nesting positions on a tombstone fixture.

There are two popular ways to use nesting positions, the first of which is shown inFigure 4-16, which illustrates a tombstone fixture in use. Every part datum on thetombstone fixture shown has its own local coordinate system assignment. Manyprogrammers feel that the arrangement shown in Figure 4-16 is the best way touse nesting positions.

The other way is to assign just one central coordinate system to the whole job asshown in Figure 4-t7 .


t /

Figure 4-77 Central coordinate system on a tombstone fixture.

Both methods are correct and it is simply a matter of personal preference as towhich one is used.

When it comes to machining a single workpiece, a preferred method is to useonly one Active Coordinate System method, but this also is just a matter oforeference,

\

system on a single part.

t

Figure 4-78 Central coordinate

lndexing Multiaxis Toolpaths

Using a single Active Coordinate System requires that only one position beindicated on the machine. This approach simpl i f ies the process and lessens thepossibility of error.

Machine Rotary Center Point

So far it has been established that every machine has its own Home Position,which is its center of the universe. Every local coordinate system is a relativelocation in that universe. Also, the intersection of the rotary axis, commonly knownas the Machine Rotary Center Point, is a relative location in that same universe.and its position is stored in the registry.

CAD/CAM System Origin

Every CAD/CAM system also has its own universe. They all have a world zero,Master Coordinate System, System Origin, and so on. Just like machine tools,all these locations are called by different names. One thing you can be sure of -none of them wi l l have the same Home Posi t ion as any other machine. The job ofa CAD/CAM user and CNC machine programmer is to al ign the worlds of both themachines and the CAD/CAM systems.

If the One Zero method - where the local coordinate system on the machine,which is the Machine Rotary Zero Point - is in use, it is possible to simplymatch the CAD/CAM System's World Zero with that location. The part must thensit in the same relative location and orientation from the Machine Rotary ZeroPoint of the system and the machine, as seen in Figure 4-19.

Figure 4-79 The Rotary Zero Point is where the two rotary center lines intersect.


It on the other hand, the multiple nesting position method is preferred, newActive Coordinate Systems must be created in the CAD/CAM system as shown inFigure 4-20.

Figure 4-2O The relationship of the part zero to the Machine Rotary Zero point.

Synchronizing Machine and CAD/CAM CoordinateSystems

These Active Coordinate Systems are the equivalent of the nesting positions(for example G54-59) on the machine. Different CAD/CAM systems establish activecoordinates in difterent ways. as shown in Fig. 4-2L. For the sake of simplicity, thefollowing description will be kept very general.

An Active Coordinate System can be established by choosing an entity, such as asolid face, an arc, two lines, normal to a surface, normal along a line, or normal toa ptane,

Indexing Multiaxis Toolpaths 6 1

,

"p{

ffe

Figure 4-27 Multiple local coordinate systems.

one of the di f ferences between programming a 3-axis machine and a mult iaxismachine is the determinat ion of where the f ixture and part wi l l be located on themach ine tab le .

On a mult iaxis machlne, exact instruct ions must be given as to where the partshould si t relat ive to the Machine Rotary Zero Point . As always, a bi t of pre-planning wi l l go a long way. Avoiding col l is ions between tools, tool-holders, f ixtures,and machine components, for example, wi l l be one of the major preoccupat ions.Creat ing an accurate l ibrary of the f ixture plates, v ises, c lamps, tools, and tool-holders in use in the plant wi l l help great ly in avoiding those potent ial col l is ions.Find the Machine Rotary Zero Point (described in Chapter 2) for every machinein the shop, and place the f ixtures on those vir tual machines in the CAD/CAIYsystem. I t is not necessary to model the whole machine, but at least the machine'stable should be modeled. Extra care should be taken that al l the models s i t ln thisal igned universe (CAD/CAM and machine).

,

Secrets of 5-Axis [,4achining

Figure 4-22 Complete Machine Simulation.

Depending on the CAD/CAM software selected, it is also possible to model andsimulate the whole machine like those shown in Fiqwes 4-22 and 4-23.


Figure 4-23 Virtual -axis horizontal machine for simulation purposes.

I t is v i ta l ly important that the "business end" of the machine be modeledaccurately, i f any simulat ion is to be useful , By the business end is meant the head,fixture, table - in other words, the parts that can actually collide. Simulation willbe discussed in more detail in a later chaDter.

o4 Secrets of s-Axis Machining

Simultaneous Mult iaxis Toolpaths

f4any people think that s imultaneous mult iaxis is the true form of 5-axis machining,when in fact, it is not necessary for all the machine axes to move at the same timefor the machine to be considered s-axis. Even a simultaneous 2-axis, rotary cutt ingmotion may be considered to be a mult iaxis toolDath.

Simultaneous mult iaxis machininq is also known as Cont inuous s-axis orTrue 5-axis machining.

The i l lustrat ion in Figure 5-1 shows a 2-axis machine cutt ing a pattern onto abowl ing bal l . This machine only has a t i l t ing B and a rotat ing C-axis. There is noZ axis. Instead, that motion is controlled by a software M code, which has an ONand OFF state - either lowering the tool onto the part, or lifting it to its referenceDosit ion.

Figure 5-7 Set-up on a 2-axis machine for engraving a bowling ball.

The example in Figure 5-2 also shows a simple mult iaxis mot ion - so simple that i tcan be programmed by hand. The program contains the fol lowing codes:

65

c01 22 .0000 F90 .

x -5 .5 A2880 .000 F50 .

GOO 25.

Figure 5-3 Sketch of simultaneous cutting on a 4-axis machine -XYZA,

Figure 5-2 A simple multiaxis set-up.

Secrets of s-Axis l\ilachining

Figure 5-4 A 4-axis machine set-up for cutting a variable-pitch thread on anauger using motions on XYZ and A axes.

Simultaneous cutt ing on a 4-axis machine is shown in Figure 5-3, and a set-upfor cutting a variable-pitch thread on an auger using 4-axis motions XYZ and A isshown in Fig ure 5-4.

Figure 5-5 i l lustrates a set-up on a simi lar machine, combining simultaneousmotions, and using a flywheel to produce a knee-joint component using the 4-axismotions XYZ and C.

Figure 5-5 The 4-axis simultaneous motions XYZ and C are shown cutting aknee-joint, using a fly-cutter.

Many parts would be impossible to machine without simultaneous multiaxis motion.In.the early days of mult iaxis machining, many parts were designed around motioninstead of as freeform CAD models.

Simultaneous Multiaxis ToolDaths

An example is the spiral bevel gear shown in Figure 5-6, which would normal ly beproduced on a special gear-cutt ing machine in an automobi le plant.

Figure 5-6 Spiral bevel gear produced on a s-axis CNC machine.

This gear was machined with the fol lowing man ual ly-generated, mot ion-dr ivencodes:

o 0 0 0 1 _c 2 0c 9 0 c 0 0 x - 3 . 7 5 Y 0 . 2 2 5 . B - 3 5 . C 0 .T lMO 6s 3 0 0 M 3s 3 0 0 0 M 0 3c 4 3 2 3 . 5 H 12 3 . 2 5G 1 z 2 . 9 F 2 4 0 .M 9 8 P 3 0 0 0 L 3 0c 9 0 G 0 0 2 2 5 . M 0 5M 3 0

0 2 0 0 0G 9 1 G 1 Z - . 1 E 5 0 .x 2 . 2 2 - . 1 C 6 0 . 8 5 . ( 4 - a x i s s i m u l t a n e o u s m o t i o n )x - 2 . 2 2 . 1 C - 6 0 . B - 5 .M 9 9

0 3 0 0 0M 9 8 P 2 0 0 0 i , 3G 9 1 G 0 0 2 . 3z r .c 7 2 .l t - L .

M 9 9


This last example is very simpl ist ic, but wi th some creat ive use of bra nching/ loopinglogic. Some shops have used this technique to produce very complex parts.

There has always been a separation between design and manufacturing. Typically,paft designers are not CNC programmers or operators. As a result, many designsdon' t take account of c lean tool mot ion, or theV include features that are hardto machine and require addit ional operat ions. In wel l - run shops, designers andproduct ion engineers work in conjunct ion, f rom the design process through tomanufactur ing. This is an ideal solut ion, but unfortunately not the norm. Workingin conjunct ion, engineers can save many hours of valuable manufactur ing t ime,tool ing, f ixture design and bui ld ing.

CAD systems have evolved drast ical ly and, as a resul t , i t is possible to design andmanufacture ever-more complex parts l ike the examples shown in Figure 5-7.

Figure 5-7 Examples of parts produced onturbine blades and rotors, impellers, pump

covers.

multiaxis milling machines, includingcomponents, brackets, and manifold

Simultaneous Multiaxis Toolpaths 69

Figure 5-7 Examples of parts produced on multiaxis milling machines, includingturbine blades and rotors, impellers, pump components, brackets, and manifold

covers.

Developing cutting strategies for these multiaxis parts entails more than justcreating toolpaths. The strategy is all about control. The goal is to create a toolpaththat causes the smoothest, most efficient, machine motion inside the machine's"sweet spot" (the optimum work envelope), while avoiding near-misses andcollisions between machine tool components, fixtures and holders.

The Optimum Work Envelope

The optimum work envelope is the space in which the machine's rotary axes rotateabout the same diameters. The fol lowing is an example.


Figure 5-8 A vertical milling machine with a trunnion-type duat rotary tabte, setup to machine a model of a human head.

Machining of a model of a human head on a trunnion-type dual rotary table isshown in Figure 5-8. The head is high above the Machine Rotary Zero point,measured along the Z-axis, but it is very close to the C-axis center point of therotary table, measured along the X and Y axes.

In programming such a job, it is best to avoid creating simultaneous rotary cuttingmotions involving the ful l range of the t i l t ing B-rotary axis (-15 and +105 degrees)while the C-axis is being rotated around its axis. Doing so will create unevenmotions between the rotarv mechanisms.

Figure 5-9 Example of part being placed far away from MRZP.

Simultaneous Multiaxis ToolDaths 7 1

In Figure 5-9 it should be noted that the B-axis move is much longer than theC-axis move, even though the angular values are the same. The reason, of course,is that the circumferences are widely different for the B and C motions. High-quality machines handle these kinds of uneven rotary motions better than lower-quality machines because they synchronize the two rotaries to arrive at the samepoint, while maintaining a constant feedrate. CAD/CAM systems can also controlfeedrates by using Inverse Time Feedrate output. A more detailed overview ofthese controls is included in the Feedrates section of this chapter. At this point, itis sufficient to know that it will be much better to place the workpiece closer to thesame rotary diameters of the speci f ic machine. as shown in Figure 5-10, especial lyi f a third-party dual-rotary table, or a lesser qual i ty mult iaxis machine are in use.

Figure 5-7O The part is placed close to the Rotary Zero Point of the machine.

Placing the workpiece close to the same rotary diameters of any particularmachine, as shown in Figure 5-10, might not always be possible. But when i t is,take advantage of this simple technique to better control motion.

Feedrates

On a 3-axis (non-rotary) machine, there is no need to specify a feedrate modebecause these machines all operate in the units/time mode.

For example, i f you designate a posi t ion as G9L G1 x7 .07f07 Y7.07107 r l -0,your machine slides will move the workpiece in a coordinated linear motion fromits current Dosi t ion to an incremental dest inat ion of x7.07107 Y7.07107 at 10inches a minute. The machine will move the workDiece exactlv 10.000 inches in astraight diagonal l ine.


Figure 5-77 A diagonal groove is machined by moving both tabte stidessimultaneously using linear interpolation,

With linear interpolation, the workpiece won't get to 10 inches/per minuteinstantly because the slides need to accelerate from zero. Once a sDeed of 10inches a minute is reached ( i f the machine is capable), i t won,t instant ly stop atits destination. Instead, the slides will decelerate to that position, but for thisexample, those lost t imes are negl ig ible. We can calculate the t ime of th is 10.0000inch move with this equat ion: 10 inches/minute = I minute.

Figure 5-72 Circular interpolation is used to move the workpiece in a circutar path.

Simultaneous Multiaxis ToolDaths

A planar c irc le cut using a c3 r-5. F10. command is i l lustrated in Figure 5-12.The resul t ing mot ion appears to be a true circ le, but i t is not. Any machine that hasthe standard three XYZ l inear axes cannot cut a t rue circ le; only an approximateone. The sl ides on these machines can move only in straight l ines. Therefore, inorder to generate a circular path, the control ler wi l l have to interpolate a circularmove by breaking the programmed circ le into a number of straight- l ine segments.On most machines, the circular tolerance can be set from inside the controlparameter sett ings. The larger the size of straight- l ine segments, the less accuratethe circ les wi l l be. A smal ier number wi l l resul t in more accurate circular cuts.

Changing the circular to lerance affects not only the circular accuracy, but also thefeedrate used for the cut. The machine wi l l have to s low down in order to maintainthe accuracy set, and the feedrate wi l l change based on the size of the arc. Largearcs can be cut with a faster feedrate than small ones.

Every quadrant of an arc includes a peak error area. which consists of the pointswhere the linear axes intersect the arc at 0, 90, 180, and 270 degrees. As themachine interpolates the circle, it needs to reverse the slide motion of its linearaxis to t ravel in the opposi te direct ion. Even i f a high feedrate is programmed, themachine's control ler wi l l l imit the executed feedrate based on the circular to leranceset in the control ler and the arc s ize current ly being executed. For this reason,calculat ing cycle t imes is not an exact science.

Multiaxis machines work with two types of feedrates:. Standard (G94 uni ts/ t ime), as descr ibed above. Inverse Time feedrate (G93)

Inverse Time Feedrate

During simultaneous mult iaxis rotary mot ions, both rotary and pivot ing axesmust ideal ly arr ive at a speci f ied rotary dest inat ion at the same t ime. Otherwise,movement on one axis will stoD to wait for the other rotarv axis to arrive. Thiswait wi l l cause the tool to dwel l in one posi t ion, which in turn, wi l l change thecutt ing pressure and def lect ion. In the best case scenario, th is delay wi l l causean unwanted tool mark on the part surface. In the worst case scenario, the pausecan even gouge the part . CAM systems handle this problem by l inear izat ion, whichbreaks up these moves into smal ler segments and appl ies control led Inverse Timefeedrates to them.

The feed/minute is specified when the tool needs to move at a specified feedrateto maintain the necessary feed per tooth to cut the material consistently. To movethe tool with that feedrate, the rotary center points need to move much faster inspace, especial ly i f longer tools versus shorter ones are being used.

The example shown in Figures 5-13 and 5-14 has only one rotary mot ion combinedwith X and Z l inear moves.

74 Secrets of 5-Axis l\ilachining

Figure 5-73 The start position for machining a complex parc.

Figure 5-74 Destination of motion from start point in Figure S-13.

Simultaneous Multiaxis Toolpaths

Looking at the two i l lustrat ions in Figures 5-13 and 5-14, i t is possible to observeand imagine the difference in travel distances between the tool tip and the rotarycenter point of the head. To maintain the programmed feed/minute on the tool t ip,the center of the rotary spindle head needs to move very quickly. This scenariocan be compared to runners on a track. Running in the inside lane of the trackcovers less distance than running on the outside lane of the track. The tool t ip isthe runner on the inside lane, and the center of the rotary is running on the outsideta ne .

In short, the machine should not be instructed to move from the current position tothe dest inat ion at X uni ts per minute. Instead, i t should be told to move from startto dest inat ion, in X amount of t ime, in a smooth interpolated mot ion, on al l theaxes involved. On Fanuc type controls, G93 signifies the staft of the inverse timemode. There must be an F command at the end of every l ine containing a G1, G2and G3 code. The Inverse Time mode will not affect rapid G0 moves,

In Inverse Time Feedrate mode, an F signifies that the move between thecurrent posi t ion and the dest inat ion should be completed in (1 div ided by the Fnumber) minutes. For example, i f the F number is 2.0, the move wi l l be completedin hal f a minute.

Inverse Time Feedrates were widely used in the early days of NC, but todaymany modern CNC controllers are capable of parsing standard feedrates intoinverse t ime and vice-versa. (A parser is a compi ler or interpreter) . Usual ly, aninverse t ime smoothing algor i thm is incorporated into this feature and i t can beenabled, or disabled, in the control ler 's parameter sett ing.

Post Processors

CAD/CAM systems generate s-axis vector lines along 3D paths. The 3D pathsrepresent the tool motion as it follows the pattern being cut. The vectors representthe indiv idual tool axis direct ions ( I lK vectors) as the tool fo l lows the 3D (XYZ)pattern. Every vector is represented by a line of code, and during toolpath creation,a resolution of these vectors can be specified, either by defining the minimumangular differences, or the linear distances between vectors, This information iswri t ten in a generic language. Depending on the CAD/CAM system, the languagemay be cal led APT, CLS, NCI, and others. Machine tool control lers do not speak orunderstand these generic languages, however they do understand many di f ferentlanguages and dialects.

The generic CAD/CAM code must be translated into a mach ine-readable language,a process that is called post processing. A post processor will calculate the axismotions needed on a specific machine to reproduce the CAM vector sequence. Thepost processor includes detai led informat ion about the speci f ic machine's physicaland computing properties that allows it to generate the required accurate G-Code.This code, in turn, wi l l govern the axis movements of the machine that are needed


to machine the part. A different post processor will be needed for every type ofmult iaxis machine in the shoD.

Post processors have built-in intelligence designed to detect rota ry limits andautomatically retract and reposition machine axes. Rotary moves are treated witha bias (not applying a neutral point of view correction to the process), based onthe layout, as well as the primary and secondary rotary axes of the machine. postprocessors will stay away, or warn of 5-axis instabilities, and they can output rotaryrapid motions as programmed high feedrates to better control every aspect of amachine's motions.

There are always two possible solutions when a post processor maps a s-axis toolorientation to a s-axis machine tool's kinematics. The post processors will choosethe best solut ion of the two. Consider the example shown in Figure 5-15.

The current posi t ion is xyz A+80.000 BO.0O0. In theory. the tool could alsoreach this same posi t ion at xyz A-80.000 8180.000, but that would beimpractical because the part would be hidden from view and the oDerator wouldsee the back side of the rotary device. Also, there is not enough y-axis travelcapabi l i ty on this speci f ic machine.

Figure 5-75 One of the two possible solutions for a S-axis position.

selecting the best s-axis position is the task of the post processor writer. Anothertask of a post writer is to solve s-axis instabilities, also known as pole singularities.These faults occur when the tool is vertical or almost vertical. Most oosts willgenerate retract moves along the tool axis in these situations. Good posts will avoiderratic retract and large repositioning moves by tracking the possible angle pairs,angle change l imits, and machine mechanical travel l imits.

Simultaneous Multiaxis Tooloaths

lYany CAM systems handle safe motions between two subsequent.toolpathoperations with post processors. These controls retract the tool into a safearea, and a s-axis machine repositions from one operation to the next.Instead of simply retracting to the Machine Home Position, safety volumes(box, hemisphere, cylinder) can be used for efficient tool retraction. Keep inmind that an efficient toolpath doesn't make erratic and unnecessary motions- it retracts the workpiece only to a minimum safe distance, and keeps thecutter engaged, whi le maintaining al l machine axes in opt imum posi t ions..

Every CAD/CAM developer has dedicated departments devoted to writing andsupporting their post processors, and there are many consultants makinga living doing the same work. There is a great need for post processorsbecause no two machines or operators are the same' Post processors can becustomized, not only to sui t indiv idual machines, but also to sui t the indiv idualuser's preferences. If a company wishes to attempt to modify its own postprocessor, most developers will provide training and documentation.

Developing a post processor for multiaxis machines takes a lot of effort,talent, professionalism, and perseverance. There are many "hackers" who aremanaging to "make i t work," but a high-qual i ty post processor is suppl ied withdetailed documentation and user-defined switches.

An exceptional post processor writer visits corporate machine builders to getinformation directly, and then develops and tests the post processor on all themachine types in use, The post processor is thus tried, tested, and certifiedby both the CAD/CAM company and the machine tool builder.


Common Simultaneous Mult iaxisToolpath Controls

A good CAD/CAM system is one of the most important tools in a modern machineshop, and wi l l provide enough control to conf ident ly dr ive any mult iaxis CNCequipment. The three major things that need to be control led are:

Cut Pattern - This pattern guides the tool's cuttlng directions.

Tool Axis Control - The orientation of the tool's center axis in 3Dspace as it follows the cut pattern.

Tool Tip Control - The geometry that the tool tip is compensated tofollow.

In addition to those three major controls, which are defined in more detail in thischapter, good-qual i ty CAD/CAN4 systems also provide addit ional col l is ion-avoida nce.This insurance wi l l recognize the tool 's cutteL shank, and holder. Di f ferent avoidancebehaviors can be invoked when any of these components comes into proximity withthe work-piece or a fixture. Different near-miss tolerances can be assigned to each ofthese tool comDonents.

Cut Patterns

Cut Patterns guide the tool along specified paths. These patterns can be simple 2Dor 3D wireframe, or sol id pr imit ives ( for example, box, cyl inder, and sphere.) CutPatterns can also be complex mult i -surface gr ids.

Some examples of cut patterns are shown in Figures 6-1 through 6-17

79

Figure 6-7 Tool motion following a 3D curve projected on to the face of a workpiece.

Figure 6-2 Tool motion following the rib's bottom edge.

Figure 6-3 A Cut Pattern is selected to slice the part in any given plane, forexample, patterns 3 or 4.


Figure 6-4 Impeller floor surfaces that use a Cut Pattern that morphs betweenthe two blade surfaces.

Figure 6-5 Cut Pattern that is parallel to the bottom hub sutface, while cuttingindividual blades.

Figure 6-6 The Cut Pattern for producing a cylindrical-spiral tool motion.

Common Simultaneous Multiaxis Toolpath Controls

Figure 6-7 Cut Pattern produced by morphing between the two edge curves ofthe floor surface.

Figure 6-8 This Cut Pattern is shown by the red 3D curve projected on to multiple

Figure 6-9 Floor sufface being cut by morphing between two 3D curves formedby the floor's outer edge curves,

su rfaces,

Secrets of s-Axis Machinino

Figure 6-7O Cut Pattern parallel to the floor surface as it spirals down eachblade.

Figure 6-77 Racing engine intake and exhaust ports machined with a spiralingCut Pattern.

'lCommon Simultaneous l\4ultiaxis Toolpath Controls

Figure 5-72 Path following a spherical Cut Pattern.

Figure 6-73 Path following a box-shaped Cut Pattern.


Figure 6-74 Axial Cut Pattern on aturbine blade.

Figure 6-75 Radial Cut Patternon a turbine blade.

Figurc 6-76 Turbine blade's foot sufface cut by morphing the Cut Patternbetween the outer edge of the foot sufface and the blade surface.

Common Simultaneous Multiaxis ToolDath Controls

Figure 6-77 Cut Pattern following the natural flow of the surface - the grid lines.

Tool Axis Control

The examples shown in Figures 6-1 through 6-17 were designed to illustratethe results produced by tool motions on various parts. It is necessary to controlthe direction of the tool axis as the tool follows the Cut Pattern. The Tool AxisControl allows orientation of the tool's center axis to be manipulated as it followsthe Cut Pattern. The sketches in Figures 6-18 through 5-25 illustrate theseconceDts

o

Figure 6-78 The Tool Axis can be lockednormal to a plane. In this example, theTool Axis will be maintained normal tothe bottom floor surface of eachindividual inseft Docket,

Figure 6-79 The Tool Axis can belocked so that it always intersects anydefined Doint on the holder side.


Figure 6-20 The Tool Axis can beIocked so that it is always aligned witha defined point at any distance as itfollows the Cut Pattern.

Figure 6-27 The Tool Axis can be forced toremain normal to one sur-face or to multiDlesurfaces.

Figure 6-22 The Tool Axis can be forced to fo ow a chain, while spiralingdown an intake or exhaust channel.

Common Simultaneous Multiaxis Toolpath Controls

6-23 The Tool Axis is controlled by the curves of the topand bottom surface edqes.

Figure 5-25 A Tool Axis can be forced torotate about anv other axis.

Figure 6-24 Lines can be drawn thatwill guide the Tool Axis as it follows aCut Pattern.


In addition to the previously described Tool Axis Control Methods, more controlsare available that allow the tool to be rotated around its tip by specifying lead, lag,and side t i l t angles, as shown in Figures 6-26 through 6-30.

Figure 6-26 Tool axis normalto a surface.

Figure 5-27 Tool axis at a lead angle.

Figure 6-29 Tool with side-tilt angle.Figure 6-28 Tool axis at a lag angle.


Newer systems even al low dynamic changes to be made to the side t i l t , or thelead/ lag angles, whi le cutt ing. The example in Figure 6-30 shows turbine blademachining in which the Tool Axis is dynamical ly control led. With this control , thetool can be provided with optimum access to all the features on the blade in allstaoes of the cut.

Figure 6-30 Dynamic side-tilt angle changes.

Tool Tip Control

In summary when CAD/CAM systems create s-axis toolpaths, they will:

. First generate a number of tool positions along the user's chosen cut Patternas shown in Fioure 6-31.

90 Secrets of s-Axis l\4achining

Figure 6-37 Generating tool positions on the cut pattern.

The systems then assign tool vectors to every one of those positions, based onthe Tool Axis Control method chosen by the usen as shown in Fiqure 6-32.

Figure 6-32 The generated tool axis vectors.

Next, they will move the tool to a desired depth along the Tool Axis, based onthe Tip Compensat ion method.


For example, surfaces generated to control a toolpath for the human head shown inFigu re 6-33.

Figure 6-33 Human head sculpted under computer numerical control.

The surfaces were generated by a scanner, and therefore they are not the bestqual i ty. The f i le may have gone through a few translat ions. The model may havebeen scanned ini t ia l ly and saved as an IGES f i le, then sent to someone who savedit as a STEP f i le. Next, i t could have gone to another shop where i t was savedagain as an IGES file. Every time a file gets translated between different CAD/CAMsystems there is a tolerance issue. It is very easy for errors to be compounded andproduce a poor qual i ty CAD model. The model may consist of thousands of surfacesand there may be gaps between them. The Tool Axis would f l ip radical ly i f i t t r iedto stay normal to al l the surfaces as i t t raveled. Fix ing the gaps would be veryt ime-consuming. A good, c lean model wi l l a lways produce a nicer Cut Pattern,stable tool axis or ientat lon, and cleaner cuts.

A handy 5-axis t r ick is to create a clean core under the poor qual i ty surfaces.This clean core is used to generate both the Cut Pattern and the Tool AxisControl . Then, compensat ion is appl ied to the tool t ip in cutt ing the outer-skin surfaces. fo l lowino the clean oattern.

92 Secrets of s-Axis l\y'achining

Figure 6-34 A clean core was created under the poor-quality surfaces and thetool was moved to positions at the set depth.

Figure 6-35 The clean core was used to generate the Cut pattern.

Coll is ion Control

I t is a given that col l is ions or gouges are always to be avoided, so why is col l is ioncontrol needed? Why aren't all CAD/CAN4 Systems designed to avoid themautomatical lv?

That first sentence above is not always true. In some instances, there is a needto gouge the dr ive surface! When would this appl icat ion be useful? Engine head-porting is a good example. The shapes of the intake and exhaust ports are verycomplex. Tradi t ional ly these shapes were carved by hand, with carving tools s imi larto the instruments used by dentists. Reproducing these complex shapes has alwaysbeen a chal lenoe.

Common Simultaneous Multiaxis Tooloath Controls

The CNC process is very good at reproducing shapes and comes in handy for thisapplication. The challenge is getting these hand-carved shapes into the CAD/CAM system. Probing is a common method used to reproduce ports, A probe is aspherical instrument that is used to touch the part and record a point in space,Touching many points wi l l record what is known as a point c loud which is a groupof points that roughly represents the part's shape. If a probe of the same diameteras the tool to be used is employed, the tool can be guided along the points in thispoint cloud to cut the part. An example of a shape to be reproduced is shown inFigure. 5-36, and a close-up of the probe in contact with the surfaces in Figure6-37.

Figure 6-36 Probe being used to generate points over the part's surfaces.

Figure 6-37 Close-up showing contact of the probe with the partb surface.


In some instances, it may be advisable to use a tighter cutting grid to obtaina better finish, or to use a different size of tool. In these conditions, it may benecessary to transform the point clouds into workable surfaces. These surfaceswould exist relative to the center of the probe and, in this situation, it would benecessary to lead the tool center on the surface, (the same place where the probecenter was) thus gouging the surface.

Figure 6-38 These port surfaces were generated on the probe's centerline. Thetool center is led on to the surfaces,

Most engine builders today use either a more sophisticated scanning method thatcompensates automatically for the probe diameter, or laser scanners/ as shown inFigure 6-39, that read the exact shapes of the ports,

Common Simultaneous Multiaxis Toolpath Controls vc

Figure 6-39 This probe sutface was generated with a laser scanner that canrepresent the true shape of the port,

Col l is ion avoidance must be used when cutt ing these complex surfaces. Col l is ioncontrol permits monitoring of the cutter's engagement with the sudace, whileensuring that none of the other features of the tool (shank, holdeq etc.) come incontact with any surfaces. Better CAM systems allow a choice of ways to avoidcollisions, and even permit "near-miss" distances to be set for different parts of thetool ,

The impel ler example shown in Figure 5-40 has twisted and warped blades,which would be impossible to cut wi th the side of a tool . These shaDes need to begenerated by stepping down on each individual blade with a ball-nose cutter. Thebottom f i l let is smal l compared to the blade height, and al though a long and skinnyball nose cutter is needed, it is not practical. A tapered-shank ball-nose cutter ispreferred, Because there is very little room between the blades, there is greatdanger of gouging, both the blade being cut, and the neighboring blade. Caut ion isalso needed at the hub surface to ensure that it doesn't qet violated bv the nose ofthe cutter.

96 Secrets of s-Axis l\rachining

Figure 6-40 A warped impeller.

Some CAD/CAM systems provide control by allowing multiple avoidance strategiesto be specified in the same path. For instance, in the above example it is possibleto:

. Specify cutting with multiple, spiraling cuts.

. Specify that cuts should start from the top and work down toward the bottomof each blade.

. Specify use of a tapered-shank ball-nose cutter.

. Speci fy the side t i l t angle that is to be maintained.

. If the cutter's shank comes within a certain distance from the blade, the tool isinstructed to tilt away, either in the lead/lag, or the side tilt directions.

. If the tool nose comes in contact with (or within a near-miss distance) of thehub surface, it is instructed to retract along the tool's axis.

o If the tool holder comes within a near-miss distance from the toD surfaces ofthe blades, the machine is stopped so that the tool can be moved out from theholder ( longer tool is needed).

This level of control allows creation of a clean, smooth cut with a rigid tapered-shank bal l -nose cutter, as shown in Figure 6-41.

Common Simultaneous l\ilultiaxis Tooloath Controls

Figure 6-47 A Clean Cut Pattern with dynamic tool axis control.

Not all CAD/CAM systems provide this amount of control. Some will only allow thedefinition of check surfaces to be avoided, but will not orovide the means to avoidthem. Keep in mind that these controls focus on col l is ions between tools. holders,f ixtur ing, and work-pieces. They wi l l not avoid potent ial col l is ions on the machine.To avoid collisions between machine components, like rotary heads or tables.machine simulat ion is needed. That subiect wi l l be covered in the next chaoter.

Additional Multiaxis Issues and Controls

Dovetail Effect

Even 4-axis, and especial ly s-axis, mot ion wi l l introduce some unique chal lenges.For example, i f a straight tool is plunged into the center l ine of a cyl inder and thenthe cylinder is rotated, a dovetail shape will be left between the start and endpositions of the tool, as shown in Figure 6-42.


EOVETAIL

Figure 6-42 The dovetail effect.

If the intention is to cut a spline with parallel walls, the tool should be moved offcenter, as illustrated in Figure 6-43.

Figure 6-43 For cutting a spiral sptine, the tool must be moved off center.

The offset amount must change for each side of the spline, and the offset amountwill depend on the pitch of the spline. Note also that the bottom center of the toolface cannot be in contact with the minor diameter.


Cutting Direction

lYost cutters are very sensitive to the cutting direction. In the 3-axis world, it iseasy to see and define cuts that are conventional or climbing, but this is not truewhen cutt ing a mult iaxis part .

Figure 6-44 lllustration of Lead Lag in milling operations.

When taking a l ight cut, s imply changing the lead/ lag angle of the tool changes thecutting direction at the tool contact point, as illustrated in Figure 6-44.

The tool engagement area also changes drast ical ly in deep or heavy cuts, such asthose using lead and lag cut engagement shown in Figures 6-45 and 6-46.


Figure 6-45milling.

Lead cut engagement in

Figure 6-46 Lag cut engagement inmillino.

The examples in Figures 6-45 and 6-46 show different engagements duringthe same cut, but changing the lead angle to a lag angle. The tool contact areachanges from the side to the bottom of the tool, Extra attention must be paid tothis aspect, especially if inserted, hollow-center, non-bottom cutting tools are inuse.

Mult iaxis Roughing

There are many instances where it is necessary to use long tools for roughing, asseen in Figure 6-47. This is usually dictated by the part features. Impellers area good example of this problem. Tall blades with small gaps between them forcethe use of a long cutter, and these cutters don't perform well with side-cuttingpressures, As the side-load increases, these tools will deflect, causing vibration,chatter, poor surface finish, and drastically shorter tool life. Multiaxis plungeroughing is a good way to remove material in these circumsrances.

Common Simultaneous Multiaxis ToolDath Controls 1 0 1

Figure 6-47 Plunge roughing

Plunge cuts should not be made to the final depth all at once. Instead, it is bestto plunge only to a manageable depth, plunge out one layer, then pick away onthe next one. The cutting pressure will be along the tool axis. This procedure willeliminate tool deflection and all its negative side effects. A typical job producedwith this procedure is shown in Figure 6-48.

Some CAD/CAM systems also have the ability to look at the shape of the stockmodel and eliminate all air-cuts from the toolpath. This ability, combined withplunge roughing, can shave off hours from high-volume roughing operat ions.Plunge roughing is not a simultaneous multiaxis cut and therefore is a more rigidcut.

Figure 6-48 This part was cut out of "green ceramic" which gets fired aftermilling. The finished component is resistant to abrasive chemicals in high-

temDeratu re environ ments.


Machine Simulat ion

Machine simulation is the safest and most cost-effective way to prove out multiaxistoolpaths. Using a mult iaxis machine to prove out programs is t ime-consuming anddangerous, both for the machine and for the operator! Running programs bl indlyon a real machine, based on a wireframe backplot in a CAD/CAM system, is just asoa nge ro us.

When CAD/CAM programmers converse about programming a mult iaxis machine,they typical ly use a special s ign language involving rotat ing arms and torsos, whi leholding up two f ingers and a thumb, s igni fy ing the r ight-hand coordinate systemin al l k inds of di f ferent or ientat ions. They visual ize the part and the machine as i tperforms an imaginary choreography. This v isual izat ion is not easy to do, especial ly i fthere are many different machine types in the shop,

Wireframe backplots portray the tool motion as it moves around a stationary part.This movement is later post-processed into machine motion and is different for everydi f ferent type of machine. The CD included with this book contains a number ofexamples showing the same part being cut on var ious machines. i t wi l l be clear thateven though the CAD/CAM backplot mot ions are the same, the machine mot ions arecomDletelv different.

With machine simulat ion, a machine's v ir tual repl ica can be shown on the comDuterscreen where the cutting process can be simulated safely. This try-out will ensurethat the program contains the most effective cut, the part is located in themachine's "sweet spot". and no fixtures, tools, or any machine components will meetunexpectedly.

I t must not be assumed that machine simulat ion is only to be used for prove-outswith the sole aim of f inding errors in the code. Instead, i t must be looked at as anadditional tool to help make clean, efficient, and accurate programs every time.With simulation, different approaches and different cutting strategies can be testedon different machines, without leaving the desk. And there is no need to tie down amachine for prove-outs. Nobody l ikes to see an expensive s-axis machine si t t ing id lewhi le programs are being tested,

People make mistakes under pressure. Even smal l mistakes on mult iaxis equipmentcan quickly add up to catastrophic proportions. Damage to the part, machine, down-t ime for repairs, repair costs, and penalt ies can real ly ruin a business. Running

1 0 3

a newr unproven/ 5-axis program bl indly on a machine, is I ike playing Russianroulet te with the gun chambers ful ly loaded. Using mult iaxis CNC equipment as aver i f icat ion system doesn' t make sense, and is much more expensive than usingsimulat ion. But with that said, nothing can subst i tute for the real th ing, Even aftersimulat ion tests, the f i rst run wi l l a lways be exci t ing. The sights, the sounds, thefeel of the cuts are i r replaceable. Machine simulat ion is not a magic bul let , but usedproperly, it is an extremely helpful tool.

Old School Samulat ionManv shops still cut foam or wax for prove-outs. Some will even replace thecutt ing tool wi th a f lexible pipe cleaner, and run the program on a f in ished part tosee if there are any interferences. They will slow down, override both the rapidmovements and the feedrates, and keep a close eye on al l possible col l is ions.I f there are any close cal ls they wi l l stop, make changes in the program, ei thermanual ly or in a CAD/CAM, and repeat the process. On a complex part , th isprocess can take days. On a complex, state-of- the-art , mult iaxis machine, th isprove-out process could cost thousands of dol lars in downt ime alone. Only ahighly-qualified operator/programmer should attempt this type of prove-out, evenif it costs more in wages.

RealitiesEven with today's advances in CAD/CAM capabi l i ty, many people st i l l manual ly edi tthe code created by their CAM system. There are various reasons for this and someof those reasons include the fol lowinq:

Post processors are not configured properly' For example, during rotaryposi t ioning moves, the rota ry brakes should be disengaged, and engaged againduring cutt ing. This brake appl icat ion is governed by M codes that vary withdifferent machines. If the post processor is not configured properly, these Mcodes wi l l need to be inserted manual ly.

A repeating pattern on the part can be called up, using subroutines.For example, an impeller has repeating features. Instead of letting the CAD/CAM write long extensive code, it is sometimes easier to take the CAM-createdcode for one feature and repeat it using subroutine logic. This procedure isparticularly useful when there is a lack of memory in the machine's controller.No matter what the reason is for using this method, you wi l l f ind that th ismore efficient program is always easier to prove out.

Manually-programmed probing routines are introduced' For example,a bra nching/looping probing routine using system or user-defined variablesmight check the part for al ignment at the beginning, or between tool changes.Then, based on the results, the probing routine would adjust the NC code toal ign with the part .

Experienced programmers tend to do more G-code editing than new programmers,New programmers tend to embrace and trust the technology more, and many areunfamil iar wi th G-code languages. As was establ ished in ear l ier chapters, CAM

104 Secrets of s-Axis l\.4achining

systems first generate generic intermediate code (APl NCI, CLS) and then postprocess that code into the machines'speci f ic G-code language. Al l NC machinesunderstand G-code, and when they read that code, they translate i t into machinemotions. Every word in that code, regardless of where it comes from - the CAMsystem or manual edi t ing - wi l l be recognized without discr iminat ion. The mostcommon quest ion is whether to s imulate the intermediate code or the G-code.

G-code Simulation Versus CAM Simulation

Only a handful of CAM systems have integrated machine simulat ion. Most of thoseonly simulate posted toolpath code (XYZABC), not the posted G-code. Some havepost processors that will post two streams of code at once - a simplified one forsimulat ion and the control l ing G-code for the machine. I f these post processors areconf igured correct ly, the vir tual machine and the real one wi l l behave exact lv thesame.

There is current ly only one machine simulat ion software program that can runtrue G-code and that is Ver icut@ by CGTech. This program has mult ip le machinecontrol lers avai lable, and can be conf igured to real ist ical ly s imulate al l knownG-code languages, including looping/branch ing logic, probing rout ines, and G andlY codes. If configured properly, the program's virtual machines will behave exactlyl ike the real ones. Note that both methods wi l l only work i f they are properlyconf ig ured.

I f the shop is programming manual ly, or does massive edi ts to the posted code,i t wi l l need simulat ion that is properly conf igured to s imulate real G-code. On theother hand, if the CAMt post processor is properly configured to drive an on-boardsimulat ion, no other s imulat ion is needed.

In ei ther instance, the quest ion to ask is "Who wi l l do this conf igurat ion?,,Conf igur ing mult iaxis machine simulat ion requires an int imate knowledge of eachmachine, the simulat ion software, and the post processor.

Configur ing Vir tual Machines For Simulat ion

Software companies have teams of dedicated professionals who spend all their timetesting and applying the software. Every CAM developer has a post departmentwhich wri tes translators (post processors) for every machines' language. Thedepartment is constant ly monitor ing new developments in the mach ine-bu i ld ingindustry and is in c lose contact wi th the machine bui lder 's appl icat ions teams.Together the teams develop factory-approved post processors. Without the effortsof the post writers, all CAM software would be useless. The ultimate end Droductof CAM software is not creating great toolpaths on a computer screen, but creatingcode that will govern the movements on specific CNC machines.

Machine Simulation 1 0 5

I f t rue G-code machine simulat ion is the goal, Ver icut by CGTech, is the bestsolut ion because their apDl icat ions team has hundreds of years of combined hands-on G-code experience and is capable of conf igur ing any type of CNC machine,even ent i re machining cel ls. The company special izes in reverse-post processing,meaning that they start wi th G-code and convert i t to machine movements, justl ike a machine's CNC control ler would.

Some CAM software packages offer mult ip le machine simulat ion interfaces.A few have direct interfaces with Vericut. Another popular choice is Machsimby Moduleworks. The equal ly-capable Moduleworks team special izes in postprocessors conf igured to produce both the simulat ion and the G-code output.

Every CAlvl and simulation software company provides post processing trainingand/or v ir tual machine bui ld ing. These courses are typical ly a few days long.Companies can opt to send employees to one of those courses or just leave theconfiguration work to the professionals.

The fol lowing is an overview of the general steps in v ir tual machine bui ld ing.

Virtual Machine Bui lding

I t is not necessary to v ir tual ly bui ld an ent i re machine including the chip conveyor,NC control ler , coolant tank, and so on. Such a process makes for s l ick s imulat ion,but the only crucial part that needs to exact ly resemble the real machine is thearea near the working envelope. These motions must exact ly repl icate the realmachine. The remainder of th is chapter wi l l cover the process involved to v ir tual lybui ld al l the major machines that were covered in Chapter 2. The steps are verysimi lar, regardless of the simulat ion software being used.

The Skeleton

The f i rst step is to bui ld the skeleton of the machine. The skeleton, or k inematicstructure of the machine, descr ibes how the machine's l inear and rotary/pivot ingaxes are connected. Every machine wi l l have a BASE, TOOL, and STOCKcomponent. The best way to see the skeleton of the machine is to stand by themachine and jog every axis. Try to imagine the machine naked, without the covers.Observe the example in Figure 7-1.

Every machine wil l have a BASE, TOOL, and STOCK component.


C "€,tor,,-.a z _

E MoDELSB-

EBrrrooelsTOOL

eY_^{JMODELS

a x__I+IMODELS

€tA--LTJMODELSsTocK_

€B MoDELS

Figure 7-7 Kinematic component tree.

The base of the machine in Figure 7-1 is hidden, to al low a better v iew of the"business-end" of the machine, The kinematic component tree (shown to the leftin Figure 7-1) descr ibes the machine (shown to the r ight in Figure 7-1). The BASEis the first component. The Z-linear axis is attached to the BASE, The B-rotary axisis connected to Z. The indentation signifies the axis priority, meaning that if youmove the Z-axis, the B-axis will move with it, because it is carried by the sameslide. The last component on this branch is the TOOL. carried by, or attached to,the B-axis.

The second branch is also attached to the BASE' starting with the y-linear axiscomponent. Observe that Y is at the same indentation as Z. The y-axis is carryingthe x-linear axis component. X is carrying the A-rotary axis component, whichin turn is carrying the STOCK, or workpiece. This kinematic component tree isthe most basic description of a machine, and is a stripped-down skeleton of themachine. There are no models attached to this skeleton, but you can tell by aglance which bones are connected together.

Many other component types can be attached to this basic structure including,fixture, tool changer, pallet changer, and robots.

Components vs Models

Depending on which simulat ion software is in use, mult ip le models can be attachedto every one of the main components. This ability to attach models enables

Machine Simulation 107

different properties to be assigned to each of the models. Unique tolerance values,colors, translucency, visibility, and reflectivity can be assigned to each model,and indiv idual models can also be included or excluded on the col l is ion-detect ionsettings.

Most machine simulation software uses STL models as a default, and some can alsouse solid primitives (block, cylinder, cone, sphere, or torus). Other software canuse its native solid models, or a mixture of all the above models.

Some popular machine examples are i l lustrated in Figures 7-2 through 7-10.

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Figure 7-2 Horizontal 4-axis machining center,

The horizontal 4-axis machining center configuration shown in Figure 7-2 isvery popular for high-volume tom bstone-fixtu re type manufacturing, Note thepallet changer, which can be adapted to service an entire pallet center. With thiscapability, multiple different jobs can be introduced into the manufacturing processwithout stopping the machine.

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Figure 7-3 Vertical 3-axis machine, converted to s-axis with a third-party dualrotary device.

The modif icat ions shown in Figure 7-3 can be adapted to sul t most 3-axis vert icalmachining centers. The dual rotary device bolts to the machine's table, instantlytransforming i t into a 5-axis machine. Some room wi l l be lost in the Z-axis workinqenvelope, but the mult iaxis capabi l i ty wi l l be gained.

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Figure 7-4 Verticat s-axis machine with a dual, rotary, nutating table'

The machine in Figure 7-4 is a dedicated s-axis Table/Table vertical machining

."nt"r- f,lot" the rigid machine base. Such a machine can handle heavy work with

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Figure 7-S Vertical s-axis machine with a trunnion-type dual rotary table.

Trunnion-type dual rotary configurations, as shown in Figure 7-5, are very popular inthe industry. This may be because they are competitively priced and easy to set upand ooerate,

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Figure 7-6 Vertical s-axis machine with a dedicated dual rotary table.

Figure 7-6 shows another example of a sturdy, dual-rotary, s-axis verticalmachining center. This machine also has the abi l i ty to spin the C-axis as a spindle,al lowing for turning work to be done.

'l'12 Secrets of s-Axis Machinino

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Figure 7-7 Horizontal/vertical s-axis Head/Table machining center.

The machine in Figure 7-7 is called VH - Vertical and Horizontal. It is a s-axisHead/Table machine, and its design allows for exceptional flexibility in addition toformidable rigidity.

lvlachineSimulation 113

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The vertical S-axis, Head/Table machine in Figure 7-8 provides an amazingcombinat ion of speed and precis ion.


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Figurc 7-9 Vertical s-axis profiler, with a dual rotary head.

Many manufacturers offer variations on the type of Head/Head configurationshown in Figurc 7-9, commonly known as a profiler. Typically these machines havelimited rotary range combined with long bed travel.

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Figure 7-7O Vertical s-axis laser machine, with a dual rotary head.

The vert ical s-axis machine shown in Figure 7-10 is used for laser-machining, butthis kind of Head/Head configuration is also very popular for milling and water-jetmachining.

Machine Simulation Interfaces

A GUI (Graphical User Interface), or form of text file, can be used to build virtualmachines. With such a program, models, or whole component branches, canbe manipulated indiv idual ly. For example, the vir tual machine can be used totranslate, rotate, or set dependencies, translucencies, or reflectivity.

Once the vir tual machine is bui l t , a l l i ts axes can be moved indiv idual ly wi th MDI(Manual Data Input) commands, or slider bars, to check if the correct models areassigned to the correct axes. These commands can also be used to check if thepositive and negative motions are correct. Remember that all simulation softwareis useless if it is not emulating the movements of the real machine. The modelsrepresenting the real machine must be accurate in relation to the business endof the machine. This area is near the work envelope and includes the spindle,fixturing, and rotary devices.

Once the physical model of the machine is built, the virtual controller must beconfigured. In a CAM system this work is done with the post processor. In Vericut,configuration is achieved with a reverse post processor. This configuration processis cr i t ical in emulat ino the behavior of the real machines.

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1 1 6 Secrets of s-Axis Machining

Using Machine Simulat ion

These days, very few people program exclusively by hand. Most people use a CAD/CAlvl system to generate code. The palt is typically either designed or imported,and then toolpaths are generated using tools f rom an internal or an externall ibrary. Machine simulat ion can be run at any t ime dur ing or at the end of th isprocess, provided the groundwork has been laid down and the machines have beenb u i l t .

The process of sett ing up machine simulat ion is very simi lar to sett ing up a realmachine. The part must be placed on the machine in the correct or ientat ion andthen the Local Coordinate System needs to be set relative to the MachineRotary Zero Position. The tools then need to be loaded into the magazine andthe Tool Length Offsets must be set correctly. This work can be time-consumingif there is no direct interface between the CAD/CAM and the simulation programs.If there is a well-configured interface, or if the simulation is an intricate part of theCAD/CAM, then sett ing up wi l l take only a few seconds of processing t ime.

Native CAD/CAM simulation loads tools from its libraries. Vericut uses its own toolmanagerf or i t wi l l bui ld a tool l ibrary automatical ly i f i t is integrated with a CAMsystem. Once the part , tools, and toolpaths are loaded, the simulat ion is readyto be run, ei ther as single blocks, or cont inuously. The simulat ion can be sloweddown or sped, and the model can be dynamical ly rotated. Some systems al lowmovements forward or backward at any time, but others don't offer this option.Some systems wi l l show mater ial removal wi th s imulat ion, and some wi l l permitanalysis and measurement of the vir tual part . Most systems wi l l s ignal i f there is anear-miss or col l is ion between any conf igured components. They wi l l a lso displayan alarm i f the l imit switches are hi t by over-travel l ing on any of the mot ion axes.Operators are able to see through models by making them invis ible, which al lowsexaminat ion of the cutt ing process in ways that are not possible on a real machine.

There are many benef i ts to machine simulat ion, which al lows di f ferent ideas to betested out without pressure. Estimated program cycle times can be accessed, tohelp determine the best one. Crashing a machine on the computer screen is not abig concern, whereas crashing a real one is a catastrophe. But not using a mult iaxismachine to i ts fu l l Dotent ial is a shame. Simulat ion al lows the best ideas fromdifferent cutting strategies, and the most efficient motion for any specific machineto be combined.

The process of setting up machine simulation is very similar to setting upa real machine. The part must be placed on the machine in the correctorientation and then the Local Coordinate System needs to be set relativeto the Machine Rotary Zero Position.

l \ i lachine Simulation ' t17

Select ing The Right MachineFor Your Appl icat ion

Making a mult iaxis equipment choice decis ion is s imi lar to choosing a car makeand model. The decision needs to be based on the intended use, budget, andpersonal i ty, a long with many other considerat ions. The mult iaxis \ \garage" includesthe equivalents of race cars, al l - terrain vehicles, buses, and luxury vehicles. Thereare general-purpose machines and there are machines made for speci f ic appl icat ions.This chapter may help narrow the search based on the specific parts beingmanufactured.

Most smal l shops enter the mult iaxis arena by adding a single- or dual-rotary uni t totheir exist ing 3-axis vert ical machining center. The addit ion of the single- or dual-rotary unit allows pafts to be manufactured more quickly and makes it possible tomachine more complex parts that were previously out of reach. This advance maycause a chain reaction. When shops get better at producing complex parts, they startto charge more for those parts. They then seek out even more challenging work tomake more money. In turn, these ventures will stretch the limits of capability of theequipment, prompting considerat ion of purchasing more new equipment.

The avai lable budget is always the big considerat ion. The pr ice of any machine wi l lreflect its quality, but as with cars, the price may also be affected by the namebrand. However, budgetary considerations are outside the scope of this book.

Machine manufacturers spend a great deal of t ime developing machines. They alsospend time on their sales and marketing efforts. Reputable manufacturers haveappl icat ions teams who instal l new equipment, t rain new customers, and provideongoing technical suppoft . They also employ dedicated appl icat ions special ists whocan prepare benchmarks, or turnkey solutions, for prospects and customers.

Regardless of the specific machine type under consideration, it is smart to researchthe reputation earned by the support services provided by different manufacturers.Most CNC equipment is sold by a dealer network. Not al l dealers wi l l maintainthe same quality of service. It is wise to visit local shops that have differentCNC equipment and talk to them about their experiences. Ask them how theirequipment is performing, what the service is l ike when there is a problem, and i fthe manufacturer provided good training. I t may also be wise to ask i f the suppl iersdel ivered on al l their Dromises.

1 1 9

trSelect a machine manufacturer that sui ts the appl icat ions cr i ter ia, and then take agood look at the variety of pafts currently being manufactured in your plant. Alsoconsider the parts you intend to manufacture in the future. Consider the fol lowingscena rios.

How many parts are typically run after each set-up?If your shop produces 500,000 of the same parts per year, i t would be wise to lookfor a dedicated machine or machines to produce that part. Investigate the possibilityof a turnkey solut ion from the machine bui lder. Such a solut ion may include acomplete machining cel l , possibly with mult i tasking machines and robot ic loaders.

Does your shop/company thrive on challenging jobs and have a reputationfor producing complex work?Some shoos like to take on work that others consider to be too difficult. Thesecompanies learn from every challenge and become better and better with everyjob. Taking on difficult jobs may be risky, but it can pay great dividends. Beforecontract ing for such demanding jobs, ensure that your mult iaxis equipment isf lexible, precise, and adaptable enough for the chal lenge.

Are your existing CNC machines waiting for programs, or are your CNCprogrammers waiting for a free machine?If existing equipment sits idle waiting for programs, then the workflow, CAD/CAM system capability, and programmers'and operators' proficiencies need to bescrut in ized. I f programmers are wait ing for f ree machines, i t is again a good ideato check the CAD/CAM system's capability. Could the cutting strategy be improved?Are the r ight tools being used? Imagine running old sty le high-speed steel tools ona modern CNC machine capable of 40,000 RPM and 1500 IPM - the l imitat ions ofcheap tool ing could hold back a very capable and very expensive machine. In thesame way, if your CAD/CAM system is obsolete, you won't be able to use your CNCequipment to i ts fu l l potent ia l .

Are you happy with the performance of your CAD/CAM system, and are youusing it to its full potential?Make sure that your CNC programmers are up-to-date with their t raining on yourCAD/CAM system to ensure it is being used to its full potential. It is much cheaperand easier to get organized, trained, become efficient, and promote teamwork, thani t is to buy a brand new machine and put i t into product ion.

Is your shop/company dedicated to a single manufacturing field, forinstance automotive, aerospace, mold & die, medical or oil?The manufactur ing f ie ld you are working in wi l l a lso af fect your choice of machinetype. There are different torque, speed, and precision requirements in every field.


New PossibilitiesAfter determining that your shop is running ful l out and needs addit ionalequipment, i t is t ime to consider new possibi l i t ies. The f i rst obviousconsiderat ion is the physical s ize of the machine, and that is dictated simplyby the size of the parts that wi l l be machined and the size of your shop f loor.The next considerat ion is the mater ial that wi l l be used, which wi i l determinethe r ig idi ty needed. The qual i ty requirements of the machine wi l l be af fectedby the expected tolerances you want to hold, and budgetary restraints mustalso be kept in mind. Aside from these propert ies, keep in mind that somemultiaxis equipment is better suited for certain types of work than others,

Head/Head Machines (with long X- or Y-axis lineartravel, but limited rotary axis travel)

The manufacture of airplane wings and fuselage panels is a good f i t for Head/Head machines. The panels are designed for strength, but are kept as l ight aspossible. There are several tapered-wal l pocket ing machines that are perfect lysui ted for swarf- type toolpaths. Typical ly these parts are made from sol id bi l letstwo set-ups, as shown in Figure B-1.

Figure 8-7 A vertical mill set-up for machining an aerospace panel.

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Selecting The Right Machine For Your Application '12'l

An airplane wing str inger is a good example of a part that is long, but very sl im.Parts like this are typically machined from special extrusions, which can be over40 feet long. Typical ly, parts l ike these were made on machines simi lar to the onesshown in Figures 8-2 and 8-3, using mult ip le set-ups and elaborate f ixtur ing.

Figure 8-2 Gantry-type Head/Head machine.

Figure 8-3 Bridge-type Head/Head machine.

The Darts would tend to deform between set-ups because material would beremoved unevenly, first from one side, then from the other, in a second setup, Themachine shown in Figure 8-4 solves this problem.


Figure 8-4 Dedicated extrusion milling machine.

The machine in Figure 8-4 is wel l sui ted for machining long extrusions. I t is as-axis machine with X, U, Y, Z and A-axes. The U-axis moves parallel with theX-axis and it has two sets of rotary jaws that are used to clamp and traverse theextrusion past the cutting tool. Cutting takes place in a narrow but rigid corridor insuccessive sections, The overall lengths of the parts are limited only by the supportsystems at ei ther s ide of the machine.

Head/Table Machines (with long X-axis travel)

Long parts, similar to the examples shown in Figure 8-5, require severe rotarymotions in the primary axis and limited rotary motions in the secondarv axis.

Figure 8-5 Typical rotary parts.

Selecting The Right Machine For Your Application 123

These Darts would be best manufactured on the Head/Table machineconfiguration shown in Figure 8-6.

Figure 8-6 Head/Table type milling machine'

The rotary pivoting configuration shown in Figure 8-6 is very suitable formanufacturing long rotary parts. The weight of the part is supported by a tailstock, and the part is rotated around its center of mass. Ineftia is an importantconsiderat ion when using mult iaxis machines' Consider the conf igurat ion forengine head porting shown in Figure 8-7, and imagine the differences in machinemovements when compared with Figure 8-8.


Figure 8-7 Head/Table engine head-port milling.

Figure 8-8 Dedicated Table/Table port milling dual rotary attachment.


The machine pictured in Figure 8-7 is designed to rotate the head around its center

of mass without generating unwanted cenfrifugal forces' The machine in Figure 8-8

nas sometning citted a "nock-and-Roll" dual-rotary device. It is designed especially

for machining-ports on engine heads. The entire fixture holding the part is rocked

una |.ori"a thioughout thelutting process to present the work to the cutter. These

fixtures need to be carefully balanced to ensure smooth motion'

Head/Table Machines

Head/Table conf igurat ions such as those shown in Figures 8-9, 8-10' and 8-11' are

urnon6 tn" most virsatile choices for a variety of other multiaxis applications. This

""rr"t]f ii ' l"ri"es from the fact that the steady rest can easily be removed and the

spa . "canbeused fo rmoun t ingadd i t i ona | f iX tu res .Cus tomized f iX tu rescana |sobebui l t to sui t special jobs.

Figures 8'9.and 8-7O Additionat versatility using multiple fixtures'

Figure 8-77 Machining an auger feed spira! for an injection molding machine'

126 Secrets oi s-Axis Machining

Figure 8-72 Machining a rotary windmill unit.

Figure 8-73 An impeller.

Figures 8-12 and 8-13 represent examples of veftical machines with long X-axistravels, but Head/Table machines are bui l t in many forms and shapes.

Selecting The Right Machine For Your Appllcation 127

Rotary Table- Tilting Head Combinations

The example shown in Figure 8-14 blurs the line somewhat between the verticaland horizontal defi nitions.

Figure 8-74 This Head/Table machine is available in both vertical and horizontalconfigurations,

The rotary-table and tilting-head configurations shown in Figures 8-15 through8-18 are not suitable for long parts, but can readily be adapted for a variety ofmult iaxis appl icat ions.

' t28Secrets of s-Axis Machining

Figures 8-75 and 8-76 Head/Table aerospacet and Head/Table automotiveapplications.

Figures 8-77 and 8-78 Two Nutating Head/Table configurations.


All rotary-table, tilting-head machines tend to rotate the workpieces around theircenters of mass while maintaining the capability to reach all their features by tiltingthe head. These machines are bui l t in many sizes and are widely used in manydifferent industries, from manufacturing small medical parts (Figure 8-19) whereprecision and speed are the main requirements. to manufacturing large earth-moving equipment parts (Figure 8-20), where r ig idi ty and horsepower are thefocu s.

Figures 8-79 and 8-2O Typical medical part, and heavy equipment componentmanufacturing.

In the mold and die industry, most of the roughing operat ions are done on 3-axis,vert ical or hor izontal machining centers. In this manufactur ing f ie ld, one of thechal lenges is cutt ing deep cavi t ies or ta l l cores, The deep cavi t ies are designedwith steep side wal ls, usual ly at angles of 1 or 2 degrees, and often require unevenfloors with small fillets along the intersection of the wall and floor surfaces, asshown in Figure 8-21. Cutt ing these f i l lets on a 3-axis machine would require long,ball-nose cutters. Small steps need to be taken, causing long cycle times. The toolis often deflected by the high cutting forces, causing vibration, excessive cutterweaq and poor surface f in ish.


Figure 8-27 Typical plastics-mold cavity.

Using a s-axis machine allows tapered ball-nose cutters to be used for this work.The tapered configuration makes the ball-nose tool much more rigid for the samediameter, and the ability to tilt the tool also allows use of a shorter cuttet as shownin Figure 8-22. More aggressive cuts can then be taken, shortening the cycle time.Deflection of the rigid tool is less, and vibration is eliminated due to the reduceddeflection. Tool life is increased, and a precise. good-quality surface finish isachieved.

Figure 8-22 Multiaxis machining allows for the use of shorter, tapered cutters,

Selecting The Right Machine For YourApplication 131

Table/Table Machines

Figures 8-23 and 8-24 show the most common configurations of Table/Tablemachines, The parts to be machined are clamped to a dual-rotary table andare rotated around the tool, Inertia is a consideration. The dual-rotary table iseither mounted on the machine table or is a dedicated dual-rotary component ofthe machine. These machines are not suited for manufacturing long parts' Thework envelope is fairly limited, especially when some tool changer limitations areconsidered, Despite the limitations, this configuration is very popular.

Figure 8-23 A popular trunnion type setup.

Figure 8-24 A dual rotary "rock and roll" fixture.


Table-mounted units are not completely rigid, but dedicated dual rotaries can beboth agile and rigid. They are equally well suited for 3+2 indexing work, and forsimultaneous multiaxis work. Some applications are shown in Figures 8-25 through8-28.

Figures 8-25 and 8-25 Machining an aerospace bracket, and a fixture component.

Figures 8-27 and 8-28 Machining rotor blades, and machining a medicalcomDonent.

Selecting The Right Machine For Your Application I , 5 J

Gantry Type Head/Head Machines

cantry type Head/Head machines, as shown in Figure 8-29, arc used for largeparts, mostly in the aerospace, oil, and wood industries, This configuration permitslong l inear t ravels. Some machines are designed to al low changes of headsin addition to tools. Rigidity and precision may not be the strong suit of thesemachines, but long reach capability is.

Figure 8-29 Water-jet/milling combination machine.

Some more machine variations are shown in Figures 8-30 through 8-33. However'it is impossible to describe all the different machine configurations that areavailable, especially because this is a constantly evolving field.


Figure 8-3O A s-axis laser cuttinq machine.

Figure 8-37 This machine presents a good compromise between lonqreach and rioiditv.

Selecting The Right Machine For Your Apptication 135

Figures 8-32 and 8-33 A 6-axis industrial robot, and a 7-axis industrial robot.

This chapter has only covered the most popular designs, and some suggestedapplications based on experience. It is recommended that engineers spendsome time on initial research when choosing a machine, research not only of themachine, but also the intended use.


Choosing a CAD/CAM System ForYour Application

Choosing the appropriate CAD/CAM system is as important, if not more important,than choosing the most sui table mult iaxis machine. There are many special izedmachines that are dedicated to specific types of work, however one CAD/CAM systemwil l dr ive al l the CNC equipment in the shoD.

It is important to make sure that the selected system can handle not only all thedifferent types of work the shop does now, but will also be capable of taking onfuture chal lenges.

CAD (Computer Aided Design)/CAM (Computer Aided Manufacturing) is alwaysreferred to as one combined system because most CAD/CAM systems offer bothdesign and manufacturing capabilities. Be aware, however, that very few excel inboth CAD and CAM.

Systems with heavy CAD emphasis have their roots in CAD and are better at solidmodeling so that they can handle large assemblies with ease. These systems haveassociativity between all the components so that when a change is made to onefeature on one part in an assembly, it will propagate throughout the entire assembly.These systems are very good at managing CAD data, but their CAM capability mayhave been added later and it often does not have the same deDth.

Systems with heavy CAM emphasis are good at everything related to toolpathcreat ion, f rom simple 2D dr i l l ing, contour ing, and pocket ing to mult i -surface andmult iaxis machining. Toolpaths can be generated for al l k inds of CNC equipmentincluding wire- and other- EDM, water-jets, lasers, lathes, mills, and multitaskingmachines. These systems have intelligent tool libraries with associated feeds andspeeds for different materials and cutter types. Instead of heavy CAD capability,these systems are very good at importing CAD data from any system, with the maingoal of generating a toolpath from that data.

Special Purpose Software

Many specialized CAD/CAM systems have been designed for specific purposes. Forexample, some shops in the mold and die industry use CAM svstems that havevirtually no CAD capability, but they can import large, complex, multisurface filesquickly. The user only needs to choose the tools and select from a short list of

' t37

automated cutt ing strategies. A toolpath is soon generated, posted, and ready-to-go. The trade-off for th is speed and ease is real ized when engineering changesare necessary, Those changes need to be made on a separate CAD system andimported back into the CAM software. Also, these specialized CAIY systems willnot suppoft any other k ind of CNC machines ( lathe, EDM, plasma, water jet , etc,)and many won' t even support s imple contour, dr i l l , or pocket rout ines. This typeof special purpose CAM software only makes sense for shops that are machininglarge mold cavi t ies day in and day out. I t may be necessary to purchase a separateprogramming seat of CAD, and maybe even another seat of general purpose CAl4.

Software that can dynamically change the feedrate throughout the cutting processis another good example of a special ized CAM feature. This feature mimics anoperator standing at the machine and overr id ing the programmed feedrates bymanual ly manipulat ing the feedrate overr ide dial . In mold and die manufactur ing,large amounts of mater ial need to be removed. The topography of mult isurfacemolds is of ten so complex that i t is impossible to maintain a constant step-over, oreven a constant depth of cut. Cutt ing forces on the tool vary great ly throughout theprocess of machining large molds and dies, and the work can take hours, days, andeven weeks. I t would be impossible to stand by the machine and ant ic ipate everymotion of the axes, and override the corresponding feedrates, but with feedrateopt imizat ion, the software wi l l vary the rate automatical ly. This opt imizat ion takesplace before any cutting is done, based on constants for volume removal rate, chip-load, surface speed, and other factors. Feedrate optimization produces constantcutting forces that are designed to lengthen tool life, increase accuracy, anddramatical ly shoften cycle t ime.

Software that is specifically designed to generate toolpaths for lathes is one moreexample of special ized CAD/CAM. This software of fers l imited CAD capabi l i ty andonly turning-specific toolpaths. The software is often built in to the controllerson certain machines, and only generates toolpaths speci f ic to that machine'sconversational language. With this type of software there is no need for a postprocessor. The approach is very direct, and that can be an advantage. Howevet itcan also be a disadvantage because these toolpaths cannot be transferred to anyother machines. Grinders, lasers, water- jets, plasma cutters, and other special izedmachines can al l operate in this same fashion.

In addit ion to CAD/CAM systems, other tools are avai lable that can close the loopbetween design and manufactur ing. Simulat ion software packages can help checkand opt imize the resul ts generated by CAM software, and are a very important l inkbetween the vir tual and physical worlds. Ensuring that toolpaths are bul let proofin the vir tual world wi l l save the shop t ime and money in the long run. These toolsshould not be over looked when the shoo is beino outf i t ted for mult iaxis work.


CAD/CAM Toolbox

Buying a CAD/CAN4 system is like buying a fully stocked toolbox, but care mustbe taken to ensure that i t contains the r ight tools for the job. Al l t radesmen havetheir own idea of the perfect set of tools. A perfect set of sharp, high-qual i ty chiselswould be useless to an electr ic ian. At the same t ime, i t would be cumbersome touse a Swiss Army kni fe as a screwdriver al l day long.

Very few CAD/CAM systems can do everything well. They all have their strengthsand weaknesses. On the other hand, very few companies need al l the powerafforded to them by a modern CAD/CAM software system. The trick is findinq ther ight bala nce.

Some CAD/CAM companies provide for the capabilities of their software to beincreased as the company grows and demands more funct ionai i tv. Most f i rst t imeCAD/CAI4 users will start off with software that can perform only simple 2D drilling,contouring, and pocketing toolpaths. Once the users become proficient, they cantake on more complex, 3D, mult i -surface machining, or mult iaxis 3+2 indexingwork. From that point , users can move into complex, s imultaneous, mult iaxismi l l ing, or even operat ion of mult i - tasking mi l l ing/turning machines.

Multiaxis CAD/CAM Considerations

Multiaxis manufacturing requires software that is very strong in CAlv. CADcapabl l i ty is needed, but most ly to import CAD f i les from al l the major CADsystems, in al l the popular CAD data formats. On top of that requirement,addi t ional CAD capabi l i ty is needed to create suppoft ing geometry for tool axiscontrol , f ixture design, or v i r tual machine bui ld ing.

High-end CAD/CAM systems are ful ly associat ive. I f a design change is made, thechange wi l l propagate through the ent i re database and wi l l modify the necessarymovements in the toolpath. This feature is helpful i f one software package is usedfor the ent i re desig n-to-ma nufactur ing process. I f a s ingle, a l l -encom passingpackage is not used, then extra cost is being incurred for associativity that cannotbe used. Unfortunately, most geometry associativity only works with nativegeometry.

Most multiaxis shops import files from a variety of customers. These files couldhave been designed in any number of CAD systems, so i t is crucial to be able toread and wri te in mult ip le CAD/CAM languages. Once the model is imported, i tis cr i t ical to have good analysis tools to analyze i t and then separate i ts majorfeatures into organized layers or levels.

After the model has been analyzed and organized, some addit ional geometrycreat ion may be needed. This geometry could include addit ional wireframe, edgecurves, l ines, arcs, points, non-tr imming surfaces, or even some sol id modelcreat ion. This work wi l l require l ight-duty CAD capabi l i ty.

Choosing a CAD/CAM System For YourApplication '139

Multiaxis CAM

The category of 3+2 indexing work requires the ability to quickly and easily changethe work planes, which are always perpendicular to the spindle/tool axis. Thecreation and manipulation of these work planes, also known as Active CoordinateSystems, should be intuitive and easy-to-use' Some systems work interactivelyby allowing the user to simply pick a solid face, an arc, two lines, three points, andsuch. to define the orientation of a new Active Coordinate System. This selectionis a light-duty capability for most CAM software.

Heavy-duty CAM capability is needed for tackling simultaneous multiaxisapplications. This capability has to be a delicate balance between control, flexibility,and ease of use, A shotgun approach doesn't work well here - the precision of arifle is needed.

consider mold and die work as an example. This work is one of the mostdemanding and accurate fields in manufacturing. Molds cannot be mass-producedbut are made one or two at a time, and they have predictable features, either acore, or a cavity, or a little of both. A good 3-axis roughing strategy will alwayswork well here. Some CAM systems can quickly and automatically analyze thefeatures and then automatically generate a toolpath to machine them' In thisshotgun approach, a wide field of targets can be covered with one shot.

Precise control is needed when it comes to driving simultaneous multiaxismachines. The following is a list of must-have tools from a well-rounded, multiaxis,CAM software toolbox. Please refer to Chapter 6 for detailed examples.

Cut Pattern ControlIt is important to have a variety of ways to define and control the pattern thatwill be followed by the cutting tool. These patterns can be anything from asimple wireframe to complex surface patterns such as that shown in Figure9 -1 .

Figure 9-7 Spiraling cut pattern on a turbine blade.


Tool Axis ControlTool axis control provides the ability to set and manipulate the center axisal ignment of the tool dur ing the cutt ing process, as i l lustrated in Figure 9-2.These controls can be dynamic or static, but it is essential that they work in apredictable, stable way.

Figure 9-2 Positions of tool axis controlled by lines.

Tool Tip ControlThe tool tip control targets the precise area of the tool tip's engagement withthe part , as shown in Figure 9-3.

Figure 9-3 Tool tip compensated to follow the outer surfaces of the work.

Choosing a CAD/CAM System For Your Application 141

Collision Avoidance MeasuresCare must be taken to avoid potential collisions between moving components/and between moving and stationary machine pads when multiaxis toolpathsare being generated, As illustrated in Figure 9-4, this particular control focuseson means to avoid collisions, particularly between the cutter, arbor, holder, andthe workDiece fixture assembly.

Figure 9-4 Dynamic shank collision avoidance.

Stock Recognition Roughing StrategiesStock recognit ion dur ing roughing wi l l save t ime. I l lustrated in Figure 9-5,stock recognition trims the toolpath to the stock size. This stock can bethe initial CAD data or the in-process material created by previous millingoperations. Multiaxis roughing can be a time-consuming affair and this featureis a must-have in creating efficient roughing toolpaths.

Figure 9-5 Plunge roughing, using stock recognition.


Machine SimulationMachine simulat ion el iminates the guesswork and the need to prove-out newmachining processes on real machines, Using a real machine to prove-out atoolpath wastes valuable production time and risks potential collisions. User-friendly and powerful virtual machine simulations, as shown in Figure 9-6, canimprove productivity tremendously, but care must be taken to configure themproperly for each machine. Please refer to Chapter 7 for detailed examples.

Figure 9-6 Properly configured virtual s-axis machines emulate the movements ofreal machines,

Post ProcessorA good post processor is the most important part of any multiaxisCAD/CAM software. Without post processing, parts can be cut only in thevirtual world and not on real machines. The role of anv CAM software is togenerate code that will drive the movements of the axes on a CNC machine sothat a part can be machined, The native CAM language must be translated tomatch with each machinet speci f ic language. Customized mult iaxis posts areusually an extra charge, It is important to find out if they are available for eachspecific machine and how much they will cost. A professional post processor isusually delivered with supporting documentation that explains its features andall the available switches to activate them. CAM software typically comes witha set of generic post processors, which are user-configurable. Ask if post-development t raining is avai lable.

Choosing a CAD/CAIV System For Your Application 143

Multiaxis CAD/CAM Training

Because of the complexi ty of mult iaxis machining, i t is not recommended thatmultiaxis programmers be self-taught. Training is a very important part ofgetting the most out of the software purchase, and the best training is hands-onthroughout the entire process. Training should include importing geometry, creatingtoolpaths, post processing, and simulat ing these toolpaths on a vir tual machine,These steps represent half the job. The next step is to learn how to set up a realmachine, find the machine's Rotary zero Point, set the tool locations, load thetoolpath into the machine's controllel and then cut the real part. Nothing canreplace the feeling of excitement associated with running a new program on a realmachine.

It is essential to find out if this kind of programming training is offered by theCAD/CAM company that responds to your request to quote. Many programmerstake three- to five-day, canned training courses, which use pre-arranged trainingsessions and step-by-step instructions. It is possible to complete these trainingcourses by simply fol lowing the careful ly la id-out steps, but there is no requirementfor the user to retain any insight into why they are following those steps. Theseuser/trainees will get back to work and not know where to start. Very specificquestions need to be asked about the training options offered.

On-l ine training courses are also an opt ion. Some of these courses are very good,offering narrated videos, and hands-on training sessions. The appeal of thesecourses is that users can take them at home at their convenience.

CAD/CAM companies also offer on-site training, This arrangement ensures that thefocus is on the operation and the parts for which the programs will be used. Thedanger with on-si te t raining is interrupt ions. Care must be taken to stay on courseat al l t imes.

What happens after t raining? The chosen CAD/CAM company should provideapplications support after training is complete. It is very helpful to have thatsupport available as a safety net for at least the first few jobs.

How about update training? As mentioned earlier, CAD/CAM software is constantlyevolving, and it is important to keep up with these changes by attending periodicupdate training sessions. User forums are also a very good way of keeping up withchanges and a good way to exchange ideas with peers.


Behind the Scenes: CAD/CAM Software Development

The software that is ultimately chosen will have a profound effect on the business.Not only wi l l the shop get the software funct ional i ty to run i ts machines, i t wi l lalso be allying itself with a company that can provide years of experience andinvaluable support . Considerable thought should be given to the company behindthe software. A well-esta blished, reputable, company can become a valuable assetand partner to the operat ion.

Understanding the development cycle of modern CAD/CAN4 systems can be helpfulwhen software companies are being researched. The following behind-the-sceneslook at the development cycle wi l l i l lustrate why i t is important to select a large,wel l -esta bl ished company as opposed to a f ly-by-night business.

CAD/CAM development is a very dynamic process. A successful CAD/CAM companyconsists of many teams of indiv iduals working toward the same common goal. Theindividuals all strive to make powerful, flexible, and user-friendly software for theend-user. This task is difficult because the more adaptive and powerful the softwareis, the more complex it becomes. Complexity and ease-of-use often conflict witheach other, and writers of good software strive to find a balance between the two.

Imagination is a very important and fundamental part of CAD/CAM development,but it can be tricky because it must be tempered with todayt (and tomorrow,s)hardware limitations. Theoretical possibilities are always restricted bV currenthardware l imitat ions. CAD/CAM design is a long-term, ongoing project, andhardware advances must be correctly anticipated and implemented into thesoftwa re.

Software development planning is done by mixed groups of indiv iduals whoinclude software engineers, mechanical engineers, appl icat ions engineers, sales,and market ing people. These groups are also heavi ly inf luenced by feedback fromexisting users. Existing users help these groups make up the "wish list,, of newtools, as well as the recommended improvements slotted for the next softwarerelease. The software developers take a close look at the.'wish list., and determinewhat can be done, when, and how.

Once the software development team has produced the first usable product,they wi l l make i t avai lable to the rest of their teams, including qual i ty control ,appl icat ions, and post development. Al l these groups wi l l conduct their ownusability tests and provide feedback. The developers will use this feedback to fixbugs, improve the interact ion, and make performance enhancements. This cvcle isrepeated cont inuously, unt i l a stable, predictable, user-fr iendly Beta version of thesoftware is created.

The Beta version is distr ibuted to a special group of end-users who wi l l conducttheir own tests. At the same time, the software manufacturer,s apDlicationsdepartment will conduct more tests by cutting real parts on real machines.

Choosing a CAD/CAM System For Your Application 145

Throughout this development process, everything is careful ly documented.The technical documentat ion group wri tes Help f i les, and training manuals aredeveloped and tested for each product.

At the very end of th is planning, development, test ing, and documentat ion process,a new version of the software is launched and monitored at every step. At thatpoint , a dedicated technical support team is ready to assist customers with anyissues that may a r ise.

But this point is not the end of the development process. The planning group keepson dreaming and making new plans. The software development team stays busyworking on those plans, and so on. A good software company has large teamsof professionals in order to be able to cont inual ly develop new and improvedsoftware tools. The work is never done because i t is l i teral ly on the leading edge oftechnology.

General Guidelines for Researching CAD/CAM Software

Start CAD/CAM research onl ine. This approach can be a great way to compare thefeatures and benefits of several different software packages. Many sites includedemo video files, which can provide a good feel for the software's interface andwill often illustrate the software's newest features. The web site will also indicatedetai ls of any local resel ler in your area.

Conversat ions with peers or wi th companies with whom the shop wi l l work areuseful to learn what kind of software they are using and why. Ask people if theyare happy with the local support , and was the software easy or hard to learn? Canf i les from outside sources be imported and exported easi ly? Were there any hiddencosts? Is the local reseller reDutable? Would thev recommend the software thev areu sing ?

Visi ts to t radeshows are strongly recommended. Tradeshow demonstrat ions areshort and are geared to show off the latest hot features of the software. Visitingsoftware companies at t radeshows also provides the opportuni ty to talk direct ly totheir corporate staff, and the staff can include people from all the different groupsresponsible for the software development. Chances are that the local resel ler mightalso be on hand to explain speci f ic features and services. Such vis i ts are a pr imeopportuni ty to learn whether you would l ike working with the f i rm's employees, andto see i f they are genuinely t ry ing to help you or just t ry ing to make a sale.

lvlost of today's modern CAD/CAM packages have very similar features, makingit extremely difficult to compare them with each other. Another problem is thatthe packages are always subject to development, and therefore are constantlychanging. Beware of anyone who makes comparisons between compet ing CAD/CAIY systems, and beware even more of people who are trying to make a sale byputt ing others down. A tradeshow is a great opportuni ty to meet the people whodevelop and support the software. In addi t ion to looking at the latest hot features


trof the software, take the t ime to assess the people you would be working with i f youdecided to purchase the software. Are they enthusiast ic about their product? Arethey behaving l ike a team, or are they shi f ty. d is interested and unhelpful?

The following are among important questions that should be askedwhen visiting software companies:

. Can you start smal l and then increase funct ional i ty as your businessgrows? Many software companies offer different levels of the software,Find out i f you can buy only the funct ional i ty you need today, and add to i tlater as the business develoos.

. Find out where your local resel ler is located, and try to meet someonefrom the company. Ask quest ions regarding training, support , post pro-cessors/ and other aspects of purchase. Make sure you are comfortablewith the resel ler because the support you receive can make or break yoursoftware exDerience.

How established is the software manufacturer? It is a good idea to find areputable company with a large user-base and support network. Find outhow many programming seats are used worldwide. Is use of the part icularsoftware at which you are looking taught at trade schools or colleges? Youmay want to consider how easy or difficult it may be to find employeesthat already know how to operate your software of choice

The next important step is to set up a demonstrat ion at your plant. The local salesrepresentat ive should vis i t your shop, Iook at your operat ion, and based on whatkind of work you do, evaluate whether the software is the r ight f i t for you. I f i t is , he/she can also recommend the proper software funct ional i ty you need. Beware of salesrepresentat ives who start wi th "Do I have a solut ion for you!" even before they seethe type of work you do.

Choosing a CAD/CAM System For Your Application

Putting It AII Together

By now, readers should have a good grasp of the mult iaxis machining process, wi th aclear understanding of the di f ferent types of machines, mult iaxis toolpath types andmachining techniques, mult iaxis CAD/CA|Y controls, s imula on opt ions, and how theyal l f i t together. To test your new knowledge, t ry to answer the fol lowing quest ions.Answering the quest ions successful ly means that you are ready to bre;k lnto the fastgrowing mult iaxis machining world.

AII quest ions wi l l be answered on subsequent pages. and rnese answers can serve asa quick reference guide for the most important lessons learned in this book.

QUrZ1.) Name three benef i ts to using mult iaxis machining techniques,

1 .

2.) Descr ibe a standard s-axis machine?

149

3,) which of the following is the standard axis convention?

A

4.) what are the three major multiaxis machine types?

5.) what are the three major building blocks of a cNc machine? (Circle three.)

B

1 .

')

3 .

. Machine table servo drive system

. Spindle RPM and horsepower

. Physical propefties of the machine

. Chip conveyor uni t

. CNC control ler capabi l i t ies

. CNC drive system

. Linear table l imit switches


i 6,) What are the most important physical positions of a multiaxis machine?

. Center of gravity, Home Base

Program Home Base, Incremental Zero Position, Spindle type

. Machine Home Position, Machine Zero Position, Program Zero Position

7.) What tools are needed to find the Machine Rotary Zero Position (MRZP)?(Circle two.)

. level

. edge f inder

. dial indicator

. maintenance manual

. hammer

8.) Descr ibe indexing/rotary posi t ioning work,

9.) What is a post processor?

Putting lt All Together ' t5 t

ANSWERS

1,) Why use multiaxis machining techniques?

. Multiaxis machining techniques are used to manufacture parts more efficientlyand accurately by eliminating extra set-ups and fixturing.

. Standard shorter tooling can be used, which results in the ability to roughmore aggressively, while increasing tool life.

. A more precise surface finish can be achieved by avoiding contact with thenon-spinning dead center of the tool.

' t52Secrets of +Axis Machining

Figure 7O-7 Multiaxis machining manufactures parts more efficiently, increasestool life, and produces a more precise surface finish,

2.) What is a standard S-axis machine?

This is a t r ick quest ion! There is no such thing as a standard s-axis machine.Mult iaxis machines are avai lable in many shapes and forms. Figure 10-2 showsexamples of the various types of s-axis machines.

Figure 7O-2 Examples of the various typesof 5-axis machines.

Putting lt All Together 153

3.) What is the standard axis convention?

Figure lO-3 The standard axis convention,

The X, Y Z linear axes shown in Figure 10-3, representing the Cartesian coordinatesystem, move in straight l ines, in plus and minus direct ions. The A, B, and C rotaryaxes rotate about the X, Y and Z axes respectively. The U, V and W axes move instraight lines, parallel with the X, Y and Z axes respectively.

4,) What are the three major multiaxis machine types?

TABLE/TABLE

HEAD/TABLE

HEAD/HEAD


Table/Table Multiaxis Machines

Figure 7O-4 Table/Table machines can be configured vertically or horizontally.

Table/Table multiaxis machines can be configured vertically or horizontally, asshown in Figure 10-4. The rotary motions are executed by the dual rotary table ofthe machine. The rotary table carries another rotary table, which in turn carries thefixture and the part. With these machine types, the part is physically rotated aroundthe tool. The weight of the part and fixture need to be handled by the machine'srota ry devices, so inertia will be a factor when considering fast movements.

Head/Table Multiaxis Machines

Figure 7O-5 Head/Table machines are very capable and versatile.


Head/Table machines are arguably the most capable of the three groups. Theycan machine large, heavy parts. On some Head/Table machines, the work pieceis held by a rotary table and is supported by a tai lstock, as shown in Figure 10-5.The work piece rotates around its own axis. The pivoting head only carries theweight of the tool and it handles the cutting pressures generated as it articulatesaround the work Diece.

The rotary axis on these machines usually has unlimited rotary motion, Some caneven spin the rotary as a lathe would. The secondary pivoting axis has an upperand lower rotary/pivoting limit,

Head/Head Mult iaxis Machines

Figure 70-6 Head/Head machines can be both vertical and horizontal.

On Head/Head machines, an example of which us shown in Figure 10-6, al lrotary/pivoting motions are executed by the head of the machine. Head/Headmachines can be both vertical and horizontal, where one axis has limited motion.Some can change heads in addi t ion to tools. Heads can be straight, 90 degree,nutat ing, or cont inuously art iculat ing. In addi t ion to mi l l ing, these machines canalso be outfitted to manipulate a water-jet or a laser.

5.) What are the three major building blocks of a CNC machine?

1. The physical properties of the machineThe physical properties of the machine are represented by the machine's skeleton.Every machine is bui l t on a unique base. The qual i ty of the i ron gives the machineits rigidity. The linear and rotary axes are stacked first onto the base, then ontoeach other. The qual i ty of the l inear s l ides and rotary bear ings give the machine


its flexibility and potential accuracy. The spindle motor's torque and horsepowerfurther define the character of the physical machine.

2. The CNC drive systemThe CNC drive system represents the muscles of the machine. The CNC drivesystem consists of components designed to move the machine's linear and rotaryaxes. These components include the servo motors. drive system, and ball screws,which are responsible for moving the machine's linear and rotary components in asmooth, preciser and rapid manner,

3. CNC controller capabilitiesThe CNC control ler is the brain of the machine. Data handl ing, avai lable on-boardmemory size, and dynamic rotary synchronization controls, are some of the thingscontrolled here.

6.) What are the most important physical positions of a multiaxismachine?

Machine Home Position - Most machinists recognize this position as the place towhich all the axes move when the machine is initially turned on and Zero return isselected, as shown in Figure 10-7.

Figure 7O-7 Machine at Home Position.


Machine Rotary Zero Position - Machine Zero Position is the intersection of therotary/pivoting axes shown in Figure 10-8. This point may be unreachable by themachine.

Program Zero Position - This position, shown in Figure 10-9, is also the partdatum location in the CAM svstem.

Figure 7O-8 Machine Rotary Zero Position.

Figure 7O-9 Program Zero Position.


7.) What tools are needed to find the Machine Rotary Zero position(MRzP)?

The tools needed to find MRZP are a level and a dial indicator.

8,) Description of indexing/rotary positioning work

Most CAD/CAM systems let the user define multiple Active Coordinate Systemsin space, and then create toolpaths using the orientation of each individualcoordinate system. As shown in Figure 10-10, the Z-axes of these coordinatesystems will align with the spindle, signaling the post processor to output rotaryindexing commands into the NC code.

Figure 7O-7O Multiple Active Coordinate Sysfe/.ns.

9,) What is a Post Processor?

CAD/CAM systems generate s-axis vector lines along 3D paths. The 3D pathsrepresent the tool motion as it follows the cut pattern. The vectors represent thetool axis direction (IJK vectors) as the tool follows the 3D (XyZ) pattern. Everyvector represents a line of code, This information is written in a generic language.

The generic CAD/CAM code must be translated into a machine-readable language.This process is called post processing. A post processor will calculate motionsneeded on a specific machine to reproduce the CAM vector model, which willgovern the machine's motions in order to cut the part. A different post processor isneeded for every type of multiaxis machine.


1O.) Definition of an axis

Any motion controlled by the NC controller, either Iinear and/or rotationalconsidered an axis.

Figure to-t7 In this example the spindle head and the quill move in the samedirection, but are controlled by two separate commands, z and W respectively.

11,) Defining a simultaneous S-axis toolpath

False. Most people believe that simultaneous multiaxis toolpaths must move all 5axes of the machine tool continuously while cutting, when in fact a single rotaryand l inear combination is considered to be simultaneous mult iaxis cutt ing motion.Typical simultaneous mult iaxis toolpaths are i l lustrated in Figures 10-12 and 10-13.

Figures 70-72 and 7O-73 Examples of simultaneous multiaxis toolpath motions'


12,) What are the three common simultaneous multiaxis CAM toolpathcontrols?

1. Cut Pattern - Guides the tool along cutting directions.

2. Tool Axis Control - Controls the orientation of the tool's center axis as itfollows the Cut Pattern.

3. Tool Tip Control - Controls the geometry to which the tool tip is compensat-eo.

In addition to the above three major controls, quality CAD/CAM systems also offeradditional collision control. Even near-miss collision avoidance of the cutter, shank,and holder can be checked against any part of the workpiece, fixture, or machinecomDonents,

Please refer to Chapter 6 for more detail.

More in Review: Multiaxis Machine Offsets

PIVOT

Figure 70-74 In addition to Tool Length compensation, multiaxis machines useother offsets including Gage Length and Rotary Pivot Distance. The Rotary Tool

Control Point Distance is the sum of Pivot Distance plus Gage Length Offset.

TANCE =

LENGTH'COMP OFFSET

Putting ltAll Together 1 6 1

Quick Reference: How to Find Machine Rotary Zero Position

For Table/Table Machines:

Figure 70-77 Step 3: Rotate A+90 and set dial indicator to Zero.

Figure 7O-75 Step 1: Level the A-axis. Figure 1O-16 Step 2: Find x,Y center.


Figure 70-78 Step 4: Rotate A-90. Dial indicator should read Zero

Figure 70-79 Step 5: log Z minus the radius ofthe rotary table diameter, andadjust gage tower height to match.

PuttingltAllTogether 163


For Head/Table and Head/Head Machines:

First, make sure that the machine head is in a perfect vertical orientation and thatthe spindle is running true.

Figure 7O-2O Step 1: Usea dial indicator to check forvert ical al ignment.

Figure 7O-27 Step2: Check if spindle isrun ning true.


Figure 70-22 Step 3: Record Z max. Figure 70-23 Step 4: Record Z min.

Z max

Z min

GL - Gage Length

R - Dowel pin radius = .5OOO

Formula to calculate Pivot Distance:

P D = Z m a x - Z m i n - G L + R

Putting ltAll Together 165

Indexing/Rotary Positioning Work Overview

Also known as 3+2 machining, indexing/rotary positioning work, illustrated inFigure 10-24, is the most basic multiaxis concept. The rotary/pivoting axes areused only for positioning, and the cutting takes place with only the three linearaxes moving. Indexing work is r ig id and precise, I t is recommended that al lpossible roughing operations be performed in this rigid state.

Figure 70-24 Indexing/rotary positioning work is the most basic multiaxisconcepL

Picking a CAD/CAM System For Multiaxis Work

When selecting a CAD/CAM system for multiaxis work, make sure it is CAMoriented, and has a powerful CAD translator. The CAD translator is very importantbecause it's likely that files will be received from many different sources. Make surethe CAM system has al l the mult iaxis controls, plus col l is ion checking. Having anonboard, easy-to-use. machine simulation is a big plus, especially when projectplanning. Machine work envelope and machine component col l is ion checking arereou i red.

In addition to the above features, it is also very important to research the CAD/CAM system developer and the local dealer. Do they provide quality training andsupport, and do they have post processors for your machine?

Please refer to ChaDter 9 for more detail.

'166Secrets of s-Axis Machining

Machine Simulat ion

Do not assume that machine simulat ion is used only for prove-outs with the soleaim of f inding errors in the code. Instead, machine simulat ion should be regardedas an addit ional tool to help make clean, ef f ic ient, and accurate programs everytime. Machine simulation permits testing of different approaches, different cuttingstrategies on different machines, without leaving the desk. There is also no need tot ie down a machine for Vour Drove-outs.

Machine simulat ion iets you bui ld a repl ica vir tual machine on the computerscreen, where cutting processes can safely be simulated to make sure that themost effective cut has been created, that the part is located in the machine's"sweet spot," and that no f ixtures, tools or any machine components are meet ingunexpectedly.

In Conclusion

Congratulat ions on the commitment to become more informed about mult iaxismachining! Mult iaxis machining is a dynamic, consta nt ly-evolving f ie ld, fu l l ofpossibi l i t ies. lYul t iaxis machine tools wi l l become more complex and capable, andCAD/CAM systems wi l l develop addit ional capabi l i t ies to control them. Users wi l lcont inual ly look for more capabi l i ty, combined with ease of use, and this demandwil l pressure the machine bui lders and CAD/CAlvl developers to combine theiref fof ts in bui ld ing machine/control ler combinat ions with bui l t - in intel l igence. Aspast t rends show, these developments wi l l open yet more possibi l i t ies, adding morecomplexi ty.

Creat iv i ty does not f i t into a box, but knowing the basic concepts wi l l a l lowengineers to think outside the box. Hopeful ly th is book has demyst i f ied thisfield and inspired you to take the next step in training yourself to become moreprof ic ient and compet i t ive with al l the tools avai lable. The best measure ofcompetency in any field is mastery of the available tools. Mere possession ofmore powerful tools doesn't make one more capable, but knowledge does.

The manufactur ing industry in general , and mult iaxis machining ln padicular, isbest sui ted for those who can think outside the box. There are always mult ip leways to solve any problem and that solution always starts with oneself. The biggestsecret of s-axis machining is the real izat ion that al l the expensive CNC machinery,CAD/CAM, and simulat ion software are mere tools. Without the knowledge to usethem properly, nothing can be accompl ished. With the avai lable tools and the r ightknowledge, al l you have to do is imagine - by applying yoursel f , your imaginat ionwi l l become a real i tv.


IndexAABC linear a{es. l5Absolute coordinate system. 5?

Active coordnrab systems,25 2'7 , 57 ,59-61 , 140Acturl part zero point, 27Aligned universc,62Avoiding collisions. 45Automatic lool changing,16.42 3

dcf ined, l4substitution,32

BBal]-nose cutters, 10,96, 130Better surface linishes. l0

(-CAD/CAM systems, 3,7. 27,

capabilities.l39multiaxis coDsiderations, I 39origin,60select ing,137soft ware developmcnt, 145

rcsearching,146tmining, l4,l

Calculating pivot disiance (PD),33,37-8, 169CAM, multiaxis, 139Can-operated multiaxis machines, 3Changeable spindle heads, 53Checking positioning repeatibjlity.'12Circular

interpolation, 73

Clean core,92CNC

controllers. 3 , 76capabi l i t ies, l3,157

drive systems, l3Collision avoidance (see Avoiding collisioDs)Common misconccptions, 4, 6. 7Complexity of rvork, 120Computer nunerical control, 3, 92Crashirg, I I 7Cut pattem,79,86 94, 140,161

Cuttnrg

dircci ion, l00strategies, 45. 70. 103, 117,138. 167variable pitch thread, 67

DDedicated multiaxis machnrcs. 9, 10Designations and directions of multiaxis machine

Desired cutter area. engaging,l0Dovetail effecl. 98Dynanic

contol of tool axis, 90, 98robry fixture offset. 16.27-8,36

EEffectivc work envelope. 16Engaging desired cutter area, l0Extrusion milling machine. 123

FFanuc progritn,34Fcedrate, T2

dynanic changes. 138inverse time,74 6opt imizai ion, l3Sstandard lime. 74

Finding theccnterof rotation. 21. 27'8pivot distance, 33, 36-9. l6 l . l6, lXYzero,23

5'axisnachine ierms, 13vector Inres,76, 159

nachines,39positioning,T

GGage

length (GL),36-9. 161tower,24,163

Ganrry type head/head machines, 122,134G codes, 29. 30. 56, 104'106

1 6 9

sinulntion. 105G 90 code.29.30G-91 code.29.30Gaphical uscrnrtel1ace, ll6

HHead/head nrultiaxis machines. 18.36 7. ll5 6.

l2l 2. 13,t . 156, i64bridge iype. 122ganlry 1ype,122. 13,1laser cutting michnre, 116. 135warcr jer miling machnre. ll6. 134

Headltablenrul t iaxisnrachnrcs, 18,31.36. 113,1123 ,1. 155

aerospace, automotive applications, 129, 133milling enginc hcad ports, 125nilling long rotary pafts. 124mdd and dic applications, 130nuiating head conbinations, 129rotafy lxble, rilthg head. 128 30various conligurations, 124 9with long X'axis tavel. 123

Ho\v CNC machines work,56History of 5 axis machining.3

II n d e x n r g , 2 l , 4 4 , 5 1 , 5 5 . 1 3 3

l ixtures,5lmethods.5ltoolpaths.49wirh rotar) devices.52wo*.:19.55

Indusrrial robots. 135Interpolation

circular,T3linear,73

Inverse tnnc leedrate, 72-4. 76

L

Lead and lag jn milling. 100Lnnihlions,,16Linear

. tx is, 14 6,34.,19.74, 106. 121, 166interpolation. 73

Local coordinate systems.25 7.56 8.61 2,117

MMachine

acl ivc coordirr te system.25 7.57 61. 140, 15'bxi lding vir tual ,64, 113 6,116-7, 139. 1,13 4, 167busnrcss cnd,6, l , 107. 125coordinate systems,25 7,56-7.61'2. 1,10. 159home posidon, 16,57.60.78. 157local coordinate slstcns, 25, 26. 6l

hone positior (MRHP), l7zero point, 21, 25-7, 36. 60 2,1 1 2, 1Mzero posit ion (MRZP). I 6 '7

,21 ,25 .21 .36,1 1 7 , 1 5 8 , 9 . r 6 2

simulrt ion,27,63-4,98. 103 6. 143. 165 7graphical user inlefaccs. I l6

using. t l7Machirlnlg

centcr conJigul"tion. 108 I l0complex worRpicccs,5cngnrc components.20prof i l ing. l l5progrrn,29rout ines.5. 104. 138spnd bevelgears.68

Machsim softwxlc, 106Maintenance issues.40Manual c lr t . t inpur (MDl),25.1l6Master

coordinalc system,60zero,26

M - c o d e . 2 l , 4 3 , 6 0Milling nachines with nvc or more axes.4:l\ 4 o , r e l i n - . , 2 r . ' 1 . u l . l l ' . I n - P l l 6 l 1 - - r )

1 5 9Mult iaxis machines.3 6. 8, 17-9,40,7,1. 124. 153

cam type.3. 140dedicated,6. 9 10. 21. 39, 52-3, 110, l2l)designilions and directions. l5physical propeties, 13. 156rorghing. 21. 101. 130, 140 2, 166

Multiple nestnrg, 58. 61

NNesling positioDs. 25. 26, 56 8, 61New possibilities, 11. 121Nunbers of parts, 120

1 7 0 Secrets of s-Axls l\,4achining

Nunerical conlrol. 3

oOld school simulatifl. 104One zero meihod,60Optimum rvork envelope. 70Odgin,26,60

PPallet chargers, 40, 54, 107-8

datum, 17, 21. 27, 58, 158zero poirt (PZP), 27 8

Plunge roughing, 101-2, 142

Probes and probing,94-5, 103',1

I'hysical properties of5-axis machines, 13Pivot

distance.33point,37 9

Pivonng spindle heads, 18,32-6, 38. 124. 156. lboPockct nr i l l ing.5.86, l2 l , l l7 9Positioning $ork. 5, 7, 8. 13,20-l, 26. 42, 49, 52,

r59 , r66

processing,3.4.8.34,40,76 8. 103-6, 138,1 4 3 7 , 1 5 9 , r 6 6

processor,3,4, 8,39,40,76 9. 10zl 6, I16, 138.1 4 3 , 1 4 7 , 1 5 9

Probing routines. 104 5Program

nnnurledi tnrg. 104subloutines. 9, ,13 -4. 10.1zcro posit ion (PZP). l6 8,25.32. 117. 158-9. 162

P r o g r d m n r i l g . . 1 q . 1 8 . 2 4 . / 5 6 . 5 4 . 6 ) . - l . l 0 : .1 0 5 . 1 3 8 , 1 4 4 . 1 4 7

.ons iderations, 46languages,3l imitr t ions.46

aQucstbns and answers, 46. I 44. I 41. 119

physical positions, 151, 157standard axis convention. 150. 154

RRcpcating pxltcrns, l0,lRotary

and pivoting axcs, 32. 74axis, 16,21,33.,12.60.71.7.1, 107. i21, 156d c v i c c s , 1 6 , 1 8 . 2 1 . 5 1 2 , l l 6 . 1 5 5xrdexing nechanisns, 5, 54mcchanisns. 6, 19, 20. 39.40 3. 52 3. 7ltool cortrol point (RTCP).33'4.36. l6l

Rotary tables,5. 8.9. 18,21,27 8.31 2. 130-2.r55 6 . r63

brakes, 21,.10, 52. l0, ld e v i c e s . 1 6 , 1 8 9 , 2 1 , 5 1 2 . 7 7 . 1 0 9 . 1 1 6 , 1 2 6 . 1 5 5dynxnic fixlurc oft.\cl (RTDFO). 16,27 8.36sinsle anddual. 6, 8. 18. 39. l l9

Roughnrg. 11,21, 101'2, 130, 140'2, 152, 166Routnrcs,5.40,42, 104 5

SSecond rotart table,18Selecfirg nachnlcs, I l9Selecting software. 137Stul l r laf trn, 19, 27,47. 63 4.98. 103 17.I38,166 7

cutling motions, 10,71mil l ing te.hniques.2lmuhiaxis toolpath conirols,79, 101,152. 161toolpaths. 5.48. 65. 78. 103, 105, 107. l2l

Special-puryose soft lvare, 137Spindle heads. changeable. 31. 53Spil"l splines,99

Standard multiaxis nomenclature. 15Slock (natcrial) option1.47. 102

rccognition,1,12Sub rout ines.3.43. 104Surlace linishes. better, 5,10

origin.60view,27

TTxblc/ lxblc mult iaxis machnrcs, l8 9.24. I10. 125,

1 3 2 , 1 5 5 . 1 6 2wjth port-nilling aft achment, 125

'171

honnion and rock and ro11Iixtules,71. 111, I32various applications. 133

3D surfacing toolpaths, 5Tilting spindle heads, 31Tombstone lixtures, 6, 40, 5 8-9, 108Tool

axiscontrol ,79,86,89,91-2,98, 139, l4l , 161,lengrh offsets, 18 , 24, I 17l ists,46, 140,145

for lathes. 138simultaneous,65plane with odgin, 27tip control, 79, 90-91, l4l

Tradeshows,146Training,1442 + 3 positioning,49

UUsing motions XYZ and C,67Unlocked rotary drives, 11U\r!V linear axes, 15

vVericut software, 1,95, 106, 116-117Verilication system, 27 , 104Visiting software companies, 1, 146-7Virtual machine, 103, 105

bui lding, l06components and models, 107configudng for simulation, 105kinematic component tlee, 107skeleton, 106

wwire franes,79, 103, 139-40World zero,26,60

xXYZ l inear axes,15.32,66 7,74

zZeroing the indicator, 22Zero posit ion, 17,21, 117. 158, 162Z-Maximum,37Z-Minimum,38

172 secrcls of s-Axis lrachining

Virtual Machining CD

All the images on this CD, including the vir tual machines, were modeled using lv lastercam@(CNC Software, Inc.) . The vir tual machines were brought to l i fe using the machine simulat ioncapabilities of l4achsim (lYoduleworks) and VERICUT6 (CGTech).

Instal lat ion

The enclosed CD should run automatically when inserted into a CD-ROlq drive. if the auto-run feature does not work. please use File I\4anager to navigate to the CD. Find the file calledIndex.html and dolrble-cl ick i t .

System RequirementsThe CD was bui l t to run oot imal lv on a PC with:

. Windows XP or Vista

. Internet Explorer (Version 7) or higher

. 1024 x 768 resolut ion (or higher)

. Adobe@ Acrobat Reader@ installed. (Go to http://www.adobe.com/downloads/ to install afree version,)

. Apple QuickTime plug-in instal led. (Go to hftp: / /www.apple.com/quickt ime to instal l afree version, )

. I f you instal l th is cD on your hard disk. you wi l l need 650 l4B free space.

Vir tual Machining CD Contents:

. over 25 Interactive Machine simulations - self-extracting executable files launchinteractive machine simulation sessions. Take control of all aspects of the simulation,including view manipulat ion, s imulat ion speed, and individual axis control . Look at themachining process from various views impossible to see on a real machjne. This offers aunique visual izat ion to help understand a var iety of mult iaxis machining concepts,

. Real Machining videos - watch a real s-axis machine pefform several differentmult iaxis cutt ing rout ines on complex simulLaneous 5-axis parts,

. v ir tual Machine Siniulat ion Videos - Watch VERICUT in act ion ;F i t elecutes machinesimulat ion and veri f icat ion on over a half dozen di f ferent examples of complex mult iaxisparts.

. Printable PDF Files - Quick Reference guides for the most important aspects of settingup a s-axis machine and common mult iaxis concepts al l avai lable as easy pr int-outs,

. Image Gal lery - See ful l color examples of many of the parts and machines foundthroughout the book.

Technical Quest ions:

Please emai l your quest ions to info@industr ialpress,com or to the author atkar lo.apro@gmail .com. Or vis i t www.5axissecrets.wordpress.com and go to the l ink for FAQS.

Secrets of 5-Axis Machining

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Transcript of Secrets of 5-Axis Machining