MACHINE TOOLS - MADE EASY.pdf

8/18/2019 MACHINE TOOLS - MADE EASY.pdf

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M NUF CTURING ENG INEERING

TOPICS COVERED – (2014-15)

1. MACHINE TOOLS – LATHE, SHAPER, PLANER, SLOTTER, DRILLING, MILLING,BROACHING, GRINDING, SUPER FINISHING, THREAD MFG,GEAR MFG, JIGS & FIXTURES, NON-TRADITIONALMACHINING, NC, CNC, DNC, NC PART PROGRAMMING.

2. WELDING – CLASSIFICATION, WELDABILITY OF COMMON METALS,METALLURGY OF WELDS, TYPES OF JOINTS, 30 DIFFERENTWELDING PROCESSES, DEFECTS, DESIGN CONSIDERATIONS,WELD SPECIFICATIONS

Dr. G. R. C. PRADEEP E-mail: [email protected] 1


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MACHINE TOOLSINTRODUCTION:The process of metal cutting in which chip is formed is

effected by a relative moment b/w the work piece and thehard edge of the cutting tool. The relative motion is produced

by a combination of rotary and translatory moments of either work piece (or) tool (or) both.

Eg:

2

Machine Tool Relative MotionWork Tool

Lathe R TShaper, Planer T T

Drilling Fixed R & TMilling T R Surface Grinding T R Cylindrical Grinding R & T R

Dr. G. R. C. PRADEEP Email: [email protected]


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LATHE – MAIN PARTS

3Dr. G. R. C. PRADEEP Email:

[email protected]


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CARRIAGE ASSEMBLY

Video1,2

SLIDE

SLIDE

4


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SPECIFICATIONS OF LATHE1) Height of centers over

bed U.K. spec.

2) Maximum swing over bed USA spec.

3) Maximum swing overcarriage

4) Maximum swing overGap

5) Maximum distance b/wcenters

6)Length of bed7) No. of speeds and

feeds etc.5Dr. G. R. C. PRADEEP Email: [email protected]


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EARLY LATHES



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EARLY LATHES



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EARLY LATHES



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EARLY LATHES



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TYPES OF LATHES1) Bench lathe: It is a very small lathe mounted on separately

prepared bench or cabinet and used for small, precision

works.



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2) Speed lathe: They do not have provision for power feedand have no gear box, carriage, lead screw etc.


Two or three

spindlespeeds areavailable bycone pulley

arrangement.They are use dfor woodturning,

polishing,metalspinning etc


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3) Engine lathe: In olden days lathe was driven by a steamengine. Hence the name is still in existence even after modern lathes are provided with motor drive.



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4) Tool Room Lathe: It is nothing but the engine latheequipped with some extra attachments for accurate and

precision work like taper turning attachment, follower

rest, collets, chucks etc. The bed is relatively small.



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5) Capstan & Turret lathes: These are semi automatic typemachines very useful for mass production (small lot sizes).Less skill is required for operator and wide range of

operations can be performed. They carry special mechanismsfor indexing their tool heads. They are provided with a fronttool post which can hold 4 turning related tools and rear tool

post which can hold 2 to 4 turning related tools. The turrets

can hold only drilling related tools. The turning tools used inthe rear tool post are reverse tools with reverse geometry.


Video3,4


15/320Dr. G. R. C. PRADEEP Email: [email protected]

Turret Indexing

Movement of turret during return stroke



Turret Indexing in Capstan and Turret Lathes

Just before indexing at the end of the return stroke, the locking pin is withdrawn by the lever which is lifted at its other end bygradually riding against the hinged wedge as shown.

Further backward travel of the turret slide causes rotation of the free head by the indexing pin and lever as shown.

Rotation of the turret head by exact angle is accomplished byinsertion of the locking pin in the next hole of the sixequi-spaced holes.



Turret Lathe



Turret Lathe Layout



Capstan Lathe



Capstan Lathe Layout

h l h


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Turret Lathe Capstan lathe1. Turret head (square (or)

hexagonal) is mounted onsaddle

1. Turret head (round (or) square(or) hexagonal) is mounted onauxiliary slide that moves on

guide ways provided on saddle2. The above arrangement gives

rigidity as forces aretransferred to bed. Hencecapable of handling heavy

jobs (up to 200mm) andsevere cutting conditions.

2. Less rigidity, vibrations occur,hence suitable for lighter andsmaller jobs (up to 60mm) and

precision work.

3 Tool travel is along entire bedlength

3. Tool travel is limited because of auxiliary slide traverse limitation.

4. Tool feeding is slow andcauses fatigue to operator hands

4. Tool feeding is fast and causesless fatigue to operator hands.

5. No tail stock 5. No tail stock


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6) Automatic lathes: These are designed so that all theworking and Job handling movements of the completeManufacturing process for a job are done automatically.

No participation of the operator is required during theoperation. They fall in the category of heavy duty, highspeed lathes employed in mass production(large lot sizes).Geneva mechanism is used for indexing the turret.

Types of automatic lathe:1) According to type of stock material

Bar automatics; Chucking automatics

2) According to No. of spindles Single spindle; Multiple spindle

3) According to the directions of the axis of m/c spindles Horizontal; Vertical


Video5,6,7,8


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h l l dl l h d l


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The general purpose single spindle automatic lathes are widelyused for quantity or mass production (by machining) of highquality fasteners; bolts, screws, studs, bushings, pins, shafts,rollers, handles and similar small metallic parts from long bars or tubes of regular section and also often from separate small blanks.

Unlike the semiautomatic lathes, single spindle automats are :• used always for producing jobs of rod, tubular or ring type and of

relatively smaller size.• run fully automatically, including bar feeding and tool indexing,and continuously over a long duration repeating the samemachining cycle for each product

• provided with up to five radial tool slides which are moved bycams mounted on a cam shaft• of relatively smaller size and power but have higher spindlespeeds


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Swiss type automatic latheThe characteristics and applications of these single spindleautomatic lathes are :

In respect of application:• Used for precision machining of thin slender rod or tubular jobs, like components of small clocks and wrist watches inmass production.•

Job size Diameter range – 2 to 12 mm; Length range – 3to 30 mm.• Dimensional accuracy and surface finish – almost as goodas provided by grinding

In respect of configuration and operation:• There is no tailstock or turret• High spindle speed (2000 – 10,000 rpm) for small jobdiameter


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• The headstock travels enabling axial feed of the bar stockagainst the cutting tools as shown

• The cutting tools (up to five in number including two on

the rocker arm) are fed radially• Drilling and threading tools, if required, are moved axiallyusing swivelling device(s)

• The cylindrical blanks are prefinished by grinding and are

moved through a carbide guide bush


Video9,10

7) S i l l h Th d i d f


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7) Special – purpose lathes: These are designed to performcertain specified operations only.Eg: Facing lathe, vertical lathe, crank shaft lathe


Video11,12,13,14


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WORK HOLDING DEVICES


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1) Chucks ----a) 3 Jaw – Self centering, smaller in size, used for round

cross sections b) 4 jaw – Not self centering, medium in size, used for round,square, rectangular cross sections.

WORK HOLDING DEVICES

) C ll t Fi d i Th i t d h d t d


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c) Collets– Fixed size. They are air operated or hand operated.Used in – Tool Room lathes, Bar Automatic Lathes,Vertical Milling m/c to hold end mills.


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d) Pneumatic Chucks – In chucking Automatics Note: In bar automatics the component is parted of fromthe bar and in chucking automatics, the component is

released from the chuck and another blank is loaded fromthe magazine.e) Magnetic – Used for ferrous metals in Lathe, Milling,

Surface Grinding machines for light works and also where

Distortion is not permitted like in aerospace components.f) Vacuum – Similar to above and used for non ferrousmetals


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2) Face plate – Used forlarge size

work piecesof round,square,

rectangular,and alsoverycomplex

geometriesnot possiblein any otherdevices.

3) C i d t h l t U d f ti g h ft


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3) Carriers and catch plates – Used for supporting shafts,mandrels for imparting rotation.

4) Centers – For supportinga) Live centre – used with

face plate b) Dead centre – used in

tail stock

5) Mandrel Used to support the work pieces and also for


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5) Mandrel – Used to support the work pieces and also forholding hollow parts to meet concentricity requirements

LiveCentre

Carrier Dog

Mandrel Face Plate

Work piece

DeadCentre

6) Steady rest mounted on bed used for long heavy jobs that


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6) Steady rest – mounted on bed, used for long heavy jobs thatdeflect centrally by self weight7) Follower rest – mounted on carriage and moves with tool,used for long thin jobs that deflect laterally by cutting force.

TOOL POST


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TOOL POST


Tool Setting on Lathe


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Tool Setting on Lathe


1. Setting the tool below the centre decreases the effective rake angleand increases the effective clearance angle. This increases thecutting forces.

2. Setting the tool above the centre increases the effective rake angleand decreases the effective clearance angle. This increasesrubbing with flank surface.

1) 2)

Effective Rake is the apparent

Rake angle w.r.t tool and work position and not the actual rakeangle provided on the tool.

TOOL HOLDERS


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HSS Tool HoldersTOOL HOLDERS


Brazed Carbide tip Tool Holders (Can be grinded)


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Brazed Carbide tip Tool Holders (Can be grinded)

Throw away Carbide Tip Tool holders (Can not be Grinded)


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Throw away Carbide Tip Tool holders (Can not be Grinded)


Box Tool Holders – Used in turret lathes to apply heavy cuts


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Box Tool Holders – Used in turret lathes to apply heavy cuts& act as travelling steadies.


OPERATIONS


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OPERATIONS1) Straight turning: Here

the work rotating aboutlathe axis, tool is fed

parallel to it, depth of cutis perpendicular to it,thus producing a straightcylindrical surface. HereDiameter is effected butLength is not effected.

2) Shoulder / Step turning:

Same as above exceptthat diameter is reducedonly up to certain length.


Video13

d

3) Facing:- Here the tool is fed


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3) Facing: Here the tool is fed perpendicular to the lathe axisand depth of cut is parallel tothe lathe axis and thus

producing a flat surface. HereLength (in Shafts) / thickness(in plates) is effected, butDiameter is not effected.


4) Knurling:- Process of embossing a diamondshaped pattern on work

surface which is used for gripping purpose.Video15,16

5) Taper turning: Operation of producing tapered surfaces


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D1D2

L θ

5) Taper turning:- Operation of producing tapered surfaces.The following methods are used

1. Swiveling of

compound rest – Any Angle, AnyCorrespondingTaper length.


D1 = Larger DiaD2 = Smaller Dia

L = Taper lengthθ = Half Cone Angle2θ= Included Angle

2 Tailstock set over Small Angle Long Job


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2. Tailstock set over – Small Angle, Long Job


S = Set over DistanceL = Total Length of Work Piece

df

θ Distance

3) Form Tool – Any Angle Short Jobs


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3) Form Tool – Any Angle, Short Jobs

4) Combined Feeds – 45 0 Chamfers


f

5) Taper turning attachment (Movement of tool is similar to


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The cross slide is delinkedfrom the saddle and is

connected to the attachmentfixed on the bed. As thecarriage moveslongitudinally, the cross

slide is moved crosswise bythe guide block whichmoves along the guide bar

preset at the desired taper

angle. This action causes thecutting tool to move at anangle to the axis of the work

piece to produce a taper.Dr. G. R. C. PRADEEP Email: [email protected]

5) Taper turning attachment

Video17

( Movement of tool is similar tocombined feed )


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Video18,19

6) Metal Spinning:- It is

the operation of pressingand forming cup shapedcomponents from sheetmetal.


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7) Spring winding:- We can wind spring on lathe. Here coiled


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) p g g p gspring can be made by passing a wire around the mandrelwhich is rotated in a chuck.

8) Misc. operations:- Drilling, boring, milling, grinding etc.


8)Misc. operations:-


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) pMilling, Grinding


9) Thread cutting:- There are different thread forms like V,


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) g ,Square, Acme, buttress etc. Here the tool has the shape of thread profile. Zero rake angle is used for form tools likethreading tool, parting tool, grooving tool etc.


V threads are the standard used on most threaded fasteners


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and are by far the most common. Due to its profile, thesquare thread is more difficult to machine than a V threadand is only used where strength and wear resistance make itworthwhile. The Acme and Buttress threads are easier tomachine.


The Buttress thread can beused only where the appliedloading is always in onedirection. It is sometimesused in bench vices. Leadscrew in lathe in combinationwith split nut uses an Acmethread which can apply loadin both directions.


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Feed Rod is provided in mediumto big size lathes and is engaged

for other lathe operations exceptthreading and operates by rackand pinion operated by changegears other gears in apron.


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Tapered threads are used for water (or) Gas pipes and


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p ( ) p p plumbing supplies, which require a water tight (or) air tight connection. Tapered threads produce a wedging actionand hence produces a pressure tight joint.


Thread Terminology:Lead – The distance a screw thread advances in onerevolution.

Pitch (P) – The distance between two successive peaks orvalleys.Lead = P for single start threadLead = 2P for double start threads - A double start thread hastwo start points.Lead = 3P for triple start threads - A triple start thread hasthree start points.

Thread-Chasing dialVideo


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Single

Double

TripleLathe spindle and lead screw must be in same relative position for eachcut. Thread-chasing dial is attachedto carriage for this purpose.

20

Back Gear


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• “Back gear" is a gear mounted at the back of the headstock and allows the chuck to rotate slowly with greatly-increasedturning power.

• Screw cutting also requires slow speeds.• With a back gear fitted, the lathe not only becomes capable

of cutting threads but can also tackle heavy-duty drilling, big-hole boring and large-diameter turning and facing; inother words, it is possible to use it to the very limits of itscapacity and strength.


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6) Total Time for Threading = Time per cut x No of cuts


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6) Total Time for Threading = Time per cut x No. of cutsTime per cut = L / (p x N)

p = Pitch = 1 / No. of threads per unit length

L = Length of W.P + Approach Length + Over Travel7) Time for Drilling = πDL / 1000fv

L = Depth of hole, D = Dia of drill8) Time for Boring = πDL / 1000fv

L = Depth to be bored, D = Starting Dia of hole9) Time for facing = L / (f x N)

L = Radius of W.P10) MRR = 1000Vfd mm 3/min


Gear Train Calculation for Thread cutting:


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1) Transformation ratio = Train value = Gear Ratio= Lead of Work piece / Lead of Lead screw

= Speed of Lead screw / Speed of Work pieceThese relations are true for threads cut in metric or inches units. Alllathes are generally provided with set of change gears having teeth from20 to 120 with a variation of 5 teeth. (20, 25, 30, 35, 40, etc). In additionthe set has gear with 127 teeth called translating gear.


For a simple Gear train,Gear Ratio =

No. of teeth on Driver Gear (On Spindle) / No. of teeth on Driven Gear (OnLead Screw)

The number of teeth on

intermediate gear has no effect on the gear ratio.

For a Compound Gear train,


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Gear Ratio =(a/b) x (c/d)

a, b, c, d = Teeth of

respective gears

SLOTTER


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INTRODUCTION:This operates almost on the same principle as that of a

shaper. Slotter was invented before shaper. Here the ramreciprocates in a vertical axis. There is no quick returnand the mechanism used for ram is Crank and connectingrod mechanism. The slotter is provided with a rotary

table that can be moved longitudinally and cross wise.The slotter is used for making regular and irregular surfaces both internal and external and also for handlingcomplex work pieces. Slotter is more robust compared to

vertical shaper.


Video1,2

TYPES


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1) Puncher slotter:A heavy, rigidmachine, for removing largeamount of metalfrom largeforgings andcastings. Thelength of strokeis very large(1.8 - 2m).


2) Precision slotter: It


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is a lighter machineand is operated athigh speeds. Usedfor accurate finish,using light cuts.

SPECIFICATIONS AND OPERATIONS


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SPECIFICATION:1. Length of stroke2. Diameter of table3. Amount of cross and longitudinal travel of the table4. No. of speeds and feeds5. Floor space required6. Net weight of the machine etc.

OPERATIONS:1)Machining slots, keyways, grooves of various shapes,

both internal and external, Internal machining of blindholes, machining of dies, punches etc.

2)Machining flat surfaces, Cylindrical surfaces, Cams,internal and external gears.



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SHAPER


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INTRODUCTION: The shaper is a reciprocating type of machine tool intended primarily to produce flatsurfaces. These surfaces may be horizontal, vertical or inclined. Here the cutting tool is given a reciprocatingmotion, and after every cutting stroke, the work is fed(during return stroke) to provide an uncut layer for machining.


Here cutting is not continuousand hence the machining isknown as Intermittent cuttingoperation. This is used for initial rough machining. Thecutting tool is a single pointtool similar to lathe.


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Video3,4

Bull Gear used in shaper to reduce the speed of rotation


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obtained from motor


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TYPES


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1. According to the type of mechanisms used for givingreciprocating motion to the ram.


a) Crank Shaper:Crank and Slottedlever mechanism isused to change rotarymotion of the drivinggear called bull gear.


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Stroke length = P 1P2 = 2AP (CB/AC)

b) Geared Shaper: Rack and pinion mechanism is used.


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Geared shapers ha vea reversible electric

motor or mechanicalmechanism whichquickly returns theram, in readiness for

another cut.

c) Hydraulic Shaper: By hydraulic power i.e. oil with


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high pressure is pumped into a cylinder with piston.



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Advantages1) Th i d i l h h h


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1) The cutting speed is constant almost throughout thestroke unlike the other shapers where the speed changescontinuously.2) Power available remains constant through out hence it is

possible to utilize the full cutting capacity of the tool.3) The ram stroke reverses quickly with out any shock asthe oil on either side of the piston provides a cushioningeffect hence vibrations are minimum. Inertia of moving

parts is relatively small.4) The range and number cutting speeds possible arerelatively large and control is simple.5) More strokes per minute can be obtained by consumingless time for the cutting and return strokes at a given cuttingspeed.


2. According to the position and travel of ram.


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a) Horizontal shaper: Reciprocates in a horizontal axis. b) Vertical shaper: Reciprocates in a vertical axis.


It has a round table that c an rotateand also can be fed longitudinallyand cross wise. Also the ram can

be reciprocated at an angle up to

100

from the vertical positionenabling machining inclinedsurfaces.

c) Traveling head shaper: The ram moves cross wise for f d d i g i ti U d f h j b h t bl


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feed during reciprocation. Used for heavy jobs where tablefeed is not possible.



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3. According to the type of design of the table:


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a) Standard Shaper: Table has only 2 movements, to givefeed.


b) Universal shaper:In addition to the 2movements, the tablecan be swiveled about

a horizontal axis parallel to the ramways and the upper

portion of the table

can be tilted about asecond horizontal axis ┴ to the first axis.

SPECIFICATIONS AND OPERATIONS


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SPECIFICATIONS:1) The max. Length of stroke or cut2) Table size3) Return time to cutting time ratio.4) Number of speeds and feeds.5) Floor space required6) Weight of machine etc

OPERATIONS ON HORIZONTAL SHAPERS:1) Machining Horizontal, Vertical, Angular surfaces2) Cutting Slots, Grooves, Key ways, Splines, External Gears

etcOPERATIONS ON VERTICAL SHAPERS:Similar to Slotters.



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(1) Cutting speed V = NL(1+m)/1000 m/minTIME ESTIMATION


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(1) Cutting speed V = NL(1+m)/1000 m/min(This theoretical formula is used in calculations)

L = Length of cutting stroke in mmm = Ratio of return time to cutting time

N = No. of double strokes per min = RPM of bull gear Note:1. In actual practice, the cutting speed changes during the

cutting stroke in the crank type and geared type shapers.Hence the average cutting speed is expressed as:V = NL(1+m) / 2 x 1000

2. The stopping point of cutting stroke in hydraulic shaperscan vary depending on the resistance offered to cutting bythe work material.


(2) Time required by cutting stroke = L / 1000V(3) Return stroke time = m x cutting stroke time= mL/ 1000V


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(3) Return stroke time = m x cutting stroke time= mL/ 1000V(4) No. of double strokes required to complete the job = W / f

W = Width of W.P.f = feed in mm (or) mm/Cutting stroke (or) mm/double stroke(5) Total time taken for one complete cut = LW(1+m)/1000fV(6) Metal Removal Rate (MRR) = 1000Vfd mm 3 / min,

where d = depth of cut in mm(7) Power consumed = K x MRR hp

where K = constant for calculating horse power consumed(8) Theoretical peak to valley height = R t = 0.5 f / tan θ mmWhere 2 θ = Angle b/w the two cutting edges in the single

point tool f /2

R t θDr. G. R. C. PRADEEP Email: [email protected]

PLANER INTRODUCTION: The planer like shaper is a m/c tool


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INTRODUCTION: The planer like shaper is a m/c tool primarily intended to produce plane and flat surfaces by asingle point cutting tool. A planer is very large comparedto shaper. In a planer the work which is supported onthe table reciprocates past the stationary cutting tool andfeed is given by the lateral movement of the tool.


Video5,6

TYPES1)Double housing planer (or) standard planer: Has two


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1)Double housing planer (or) standard planer: Has twovertical housings connected by a cast iron member on top.Table is mounted on the bed and can reciprocate. The Cross


rail can move up and down on thevertical housings and one or two toolheads provided can travel cross wisefor tool feed across the cross rail.

2) Open side planer: Only one side housing and the crossrail is suspended as cantilever Used for very wide Jobs


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rail is suspended as cantilever. Used for very wide Jobs.


3) Divided Table Planer: Also called Tandem Planer. Thistype of planer has two tables on the bed which may be


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type of planer has two tables on the bed which may bereciprocated separately together. This type of design savesmuch of the idle time while setting large no. of identical

pieces on the machine.


TABLESCROSS RAIL

4) Pit planer: It is a massive construction. The table isstationary the column carrying the cross rail reciprocates


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stationary, the column carrying the cross rail reciprocates


on massiv ehorizontalrailsmounted on

both sidesof the table.Suitable for very largeworks.

5) Edge or plate planer: This is specially intended for squaring and beveling the edges of steel plates used for


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squaring and beveling the edges of steel plates used for different pressure vessels and ship building works.


SPECIFICATIONS AND OPERATIONSSPECIFICATIONS:


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SPECIFICATIONS:1.The size of the largest rectangular solid that can

reciprocate under the tool.2. No. of speeds and feeds available,3. Floor space reqd.4. Net wt. of machine etc.

OPERATIONS:(1) Planning flat horizontal, vertical, angular surfaces

(2) Slots and grooves.



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DRILLINGINTRODUCTION: A drilling machine


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INTRODUCTION: A drilling machinewas primarily designed to originate ahole, but it can also perform a No. of similar operations. In a drillingmachine holes may be drilled quicklyand at low cost. The hole is generated

by the rotating edge of a cutting toolknown as the drill which exerts largeforce on the work clamped on the table.The cutting motion is provided byrotating the drill and feeding is done bygiving rectilinear motion to the drill inthe axial direction. Here the drill usedhas two cutting edges called lips.


Video1

TYPES(1) Portable drilling machine:


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(1) Portable drilling machine:This type of D.M. can be operated with ease anywherein the work shop and is used for drilling holes in work

pieces in any position which cannot be drilled in astandard D.M. The entire D.M. including the motor iscompact and small in size. The max. size of the drill thatcan accommodate is not more than 12 to 18 mm.


(2) Sensitive D.M. It is a smallmachine designed for drilling


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machine designed for drillingsmall holes at high speed in lightand small jobs. The base of themachine may be mounted on a

bench or on the floor. There isno arrangement for theautomatic feed of the drillspindle. High speed and handfeed are necessary


for drilling small holes. As the operator can sense the progress of the drill it is called S.D.M. Drills size is 1.5to 15.5 mm can be used in this machine. Super sensitiveD.M. are designed to drill holes as small as 0.35 mm andcan be rotated at a speed of 20,000 rpm or above.

(3) Upright D.M.: This is designed for handling medium sized W P It is


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handling medium sized W.P. It issimilar to a S.D.M. but is heavier and larger than S.D.M. and issupplied with power feedarrangement.a) Round Column Section (or) Pillar D.M.: It consists of round columnand a round table. The table can bemoved up and down on the column for accommodating W.P. of differentheights. The table may be rotated360 o about its own centre. The max.size of the hole that can be drilled isnot more than 50mm.


(b) Box Column SectionUpright D M : The upright


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Upright D.M.: The uprightD.M. with box columnsection has a square tablefitted on the slides at thefront face of the machinecolumn. Heavy box columngives the machine strengthand rigidity. The table israised or lowered by anelevating screw that givesadditional support to the table.Heavier W.P. and holesmore than 50 mm dia can bedrilled by it.


(4) Radial D.M: It is intended for drilling medium tolarge and heavy W.P. It consists of a heavy, round


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large and heavy W.P. It consists of a heavy, roundvertical column mounted on a large base. The columnsupports a radial arm which can be raised and lowered toaccommodate work pieces of difference heights The armmay be swung around to any position over the work bed.The drill head containing mechanism for rotating andfeeding the drill is mounted on the radial arm and can bemoved horizontally on the guide ways and clamped atany desired position. This can be further classified as


(a) Plain RDM.:- It has the movements explained above.


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(b) Semi Universal RDM:- In addition tothe above 3 movements, the drill head


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,can be swung about a horizontal axis tothe arm. This 4 th movement of the drillhead permits drilling hole at an angle tothe H.P. other than normal position.


(c) Universal RDM:- In addition tothe above 4 movements the drillhead may be rotated on ahorizontal axis. All these 5movements enable it to drill on aW.P. at any angle and in any plane.

(5) Gang D.M.: When a No. of single spindle D.M. columns


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g pare placed side by side on acommon base and have acommon, work table, themachine is known as G.D.M.In a G.D.M. 4 to 6 spindlesmay be mounted side by side.The speed and feed of spindlesare controlled independently.


This type of machine is specially adapted for productionwork. A series of operations may be performed on the work

by simply shifting the work from one position to the other on the work table each. Spindle may be set up properlywith difference tools for different operations. Video 2, 3

(6) Multiple spindle D.M.: The function of the multiplespindle D.M. is to drill a No. of holes in a piece of work


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p psimultaneously and to reproduce the same pattern of holesin a No. of identical pieces in a mass production work suchmachines have several spindles driven by a single motor andall the spindles holding drills are fed into the work.Simultaneously. Feeding motion is usually obtained byraising the work table. But the feeding motion may also besecured by lowering the drill heads. The spindles are soconstructed that their centre distance may be adjusted in any

position as required by various jobs within the capacity of thedrill head. For this purpose, the drill spindles areconnected to the main drive by universal joints. The spindlesare connected by a number of planetary gears so that evendifferent size drills can be loaded.



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Video

4,5

7) Deep Hole Drilling machine: Special machine and drillsare required for drilling deep holes in rifle barrels, long


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q g p gspindles, oil holes in crank shafts, long shafts etc. Themachine is operated at high speed and low feed. A long

job is usually supported at several points to prevent anydeflection. The work is usually rotated while the drill isfed into the work. This helps in feeding the drill in a st.

path. The machine may be Horizontal type (or) Verticaltype. The drill is withdrawn automatically each time whenit penetrates in to the work to a depth equal to its dia.This process permits the chip to clear out from thework.


Video6,7,8


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There are different types of deep hole drilling processes andare categorized by how the cutting coolant flushes heat and


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g y gchips from the cutting face. They are:

Gun drilling - The cutting tool is astraight fluted solid rod that has ahole bored down the center. Coolantis pumped through a hole in the

inside of the drill. It flows back outside the drill, through the flute,

bringing thechips with it.

Drilling size is3-50 mm.

BTA / STS (Boring and Trepanning Association / SingleTube System) - The cutting tool is a tube. Coolant is


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y ) g pumped around the outside of the cutting tool at heavy pressure and carries chips out through the center of the tube.Very high penetration rates can be achieved with this systemalong with good surface finish. Depth to Diameter ratio ishighest among the three methods.Because tubeshave minimumsizes, this is onlyan acceptabletechnology for holes of over 15mm and up to600 mm.

Examples of Deep Hole Drilling


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Specifications1. Max. size of drill that the machine can operate,


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2. Max. spindle travel

3. Table diameter / size4. Morse taper No. of the drill spindle5. No. of spindle speeds and feeds available.6. Floor space required7. Net wt. of the machine


TERMINOLOGYDrills are Tang


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manufacturedas:1. Straight

shank drills(up to ϕ13.5 mm)

2. Taper shankDrills ( ϕ14.0 mm

onwards)


g

Shank

Neck

Body

Tip


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Drilling Machine Spindle

Drill Chuck with Chuck key

Drift Sleeve

Morse taper is provided onall drilling accessories and

inside drilling machinespindle

DRILL GEOMETRYLip angle/ Tip Angle/ Point Angle


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Land / Margin: It maintains the alignment of the drill sothat hole is straight and to the right size.


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Helix angle: Angle formed b/w a plane containing drillaxis and the leading edge of land. Based on the value of the


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angle the drills can be classified as1) Slow spiral series: 12 o to 22 o - Used for brass, bronze,CI that produce broken chips. They provide less lifting

power, but are stronger, used for shallow holes. Also usedin horizontal applications where drill is not rotating.2) Regular spiral series: 28 o to 32 o - most widely used3) Fast/High spiral series: 34 o to 38 o – Used for softer ferrous and non-ferrous materials producing long stringlike chips. They provide great lifting power, but are weak,

used for deep holes.



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Lip angle: Angle formed b/w the cutting edges. Smaller pointangles results in lower effective rake. Effect of change in


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effective rake is negligible on drill performance. Less pointangles generate wider and thin chips. Higher point anglesgenerate narrow and thick chips. Increase in point angleincreases the cutting efficiency of the drill because mostmaterials are cut efficiently in the form of thick chips. Smaller the point angle, longer is the lip length and hence reduces load

per unit length of the lip and helps in resisting the wear caused by abrasive action during machining of metals like C.I.


Lips are the cutting edges that exten d from thecentre of the drill to the outer diameter

1) M.S. 118 0 (< 180 HB)2) Steel 118 0 (180 - 280 HB)


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3) Steel 135 0 - 140 o (280 – 380 HB)

4) Grey C.I.

900

(< 180 HB)5) Grey C.I. 118 0 (180 - 280 HB)6) Chilled C.I. 135 0 – 140 0 (> 350 HB)7) Aluminum 118 0

8) Copper 118 0

9) Bronze 118 0

10)Brass 111 0


Clearance / Lip relief Angle:Angle formed b/w flank and a


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plane normal to drill axis at thetip of the drill. Large angles

(80 –12 0) are used for ductilematls. to compensate elasticrecovery. Small angles (6 0 –8 0)are used for brittle matls.


OPERATIONS1) Drilling – Process of making hole in solid body.


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2) Boring – Enlarging a hole completely with an adjustabletool with only one cutting edge.

3) Counter boring - Enlarging one end of the hole to forma square shoulder with original hole to avoid projectionsin assemblies.

4) Counter sinking - Making a cone shaped enlargement to provide a recess for a screw head.


5) Reaming – Sizing and finishing a small unhardened hole.a) Straight flute reamer is used for


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a) b) c)

through holes in materials that donot form chips like C.I, Bronze,Brass. They form fine powder thatwill fall by gravity.

b) Left hand spiral flute reamer isused for through holes in other materials and is very effective asthey push the chips out of thethrough hole.c) Right hand spiral flute reamer is used for blind holes as they pullthe chips out of them.Chucking or M/c Reamers

Manual Reamer &Wrench

d) Rose reamers are primarily used for roughing prior tofinal reaming. The cylindrical part of the reamer has no


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cutting edges, but merely grooves cut for the full length of the reamer body, providing a way for the chipsto escape and a channel for lubricant to reachthe cutting edges. To prevent binding they havea slight back taper. The cutting edges at the endare ground to a 45 0 bevel.

e) Shell reamers are similar to cutting portion of achucking reamer. They are supplied without a shank and


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has a hole through the center. A arbor is used inconjunction with the shell reamer, the slots in the reamer engage lugs on the arbor for driving power.

6) Lapping – Sizing and finishing a hole already hardened.7)Tapping–Process of making internal threads in small holes.


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8) Spot facing – Process of smoothing and squaring thesurface around the hole or seat for a nut (or) head of ascrew for burr removal.


Machine Tap with holder Manual Tap

Spot facing tools with pilot

B


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Centre Drill used for making acentre impression on surface forlocating the drill point.

Burr formation

duringdrilling

9) Trepanning – Operation of producing a hole by removingmetal along the circumference of a hollow cutting tool. Usedf d i l h l i l t


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for producing large holes in plates.

Video9,10,11

TIME ESTIMATION1) Cutting speed, V= πDN / 1000 m/min


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2) Machining Time, T = L / (f x N) = L / f m

L = L 1 + L 2 + L 3 + L 4L1 = Depth of holeL2 = Approach lengthL

3 = Length of tip = 0.29D= 0.5D / tanθ

(where, 2 θ = Lip angle)L4 = Over Travel

3) Depth of cut, d = D / 24) MRR = πD2fN / 4 = πD2f m / 4


MILLINGINTRODUCTION:A illi hi i


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A milling machine is amachine tool that removes

metal as the work is fedagainst a rotating multi

point cutter. The cutter rotates at a high speed, and

because of the multiplecutting edges it removesthe metal at a very fast rate.The first milling machinecame into existence inabout 1770 and was of French origin.


TYPES1. Column & knee type: Most commonly used for

l h k Th bl i d h k


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general shop work. The table is mounted on the kneecasting, which in-turn is mounted on the vertical slides of

the main column. The knee is vertically adjustable onthe column, so that the table can be moved up and downto accommodate work of various heights. The table can

be moved longitudinally and cross wise on the kneecasting. Classification of this type is based on methods of supplying power to the table, diff. movement of the tableand diff. axis of rotation of the main spindle.


(a) Hand milling machine Feeding is done by hand andused for light and simple operations like slots, grooves,k h l bl b h h l l


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keyways. This is available in both horizontal & verticalmodels Table movements are as above.


(b) Plain millingmachine This is ah i l


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horizontal typemilling m/c. This ismore rigid andsturdy, for heavywork, can be fed byhand or power.Table can be fed asabove.


Video

1,2

(c) Universal millingmachine This is also ah i l illi


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horizontal type millingm/c. In addition to 3movements in plainmilling machine the tablehas a fourth movementi.e. it is fed at an angle tomilling cutter. Thisenable it to performhelical milling. Thismachine can producespur, spiral, bevel gears,twist drills, reamers,milling cutters etc.


(d)Omniversalmilling machine Thi i h i l


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This is a horizontaltype milling m/c. Theextra fifth movementis the table can betilted in vertical

plane by providing aswivel arrangementat the knee. Thisenables milling inany plane. Taper spiral groves inreamers, bevel gearsetc can be done.


(e) Vertical milling machineHere the position of the

i dl i i l d ┴


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spindle is vertical and ┴ tothe work table. The spindlehead is clamped to thevertical column and can beswiveled at an angle . Alsothe spindle head can beadjusted up / down relativeto work. The tablemovements are same as

plain milling machine.


Video3,4

2. Plano Miller:It resembles a planer. It ish dl h d


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having two spindle headsadjustable in vertical andtransverse directions. It hasa cross rail which can beraised or lowered along withcutters. Hence no. of work surfaces can be machinedsimultaneously, therebyreducing production time. Ina plano miller, the table has


feed movement instead of reciprocation. Hence the tablemovement here is much slower than planning machine.

Video5,6

3. Rotary table Machine Amodification of vertical milling

hi d t d f hi i g


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machine adopted for machiningflat surfaces. A No. of work piecescan be mounted on a circular tablewhich rotates about vertical axis.The face milling cutters can bemounted on tow (or) more verticalspindles and can be set at diff.heights relative to work so thatwhen one cutter is roughing theother is finishing them. Continuousloading and unloading of work

pieces can be done by the operator while milling is in progress.


4.Planetary millingmachine: Here the

k i h ld


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work is heldstationary while therevolving cutter /cutters move in a

planetary path tofinish a cylindrical


surface on the work either internally / externally /simultaneously. Thismachine is particularlyadopted for milling internal/ external threads of different

pitches.

Video7,8

5. Pantograph milling machine It can duplicate a job by using a pantograph mechanism which permits the size othe work piece reproduced to be smaller than equal to or


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the work piece reproduced to be smaller than, equal to or greater than the size of a template or model used for this

purpose. A pantograph is a mechanism that is generallyconstructed of four bars or links joined in the form of

parallelogram. Pantograph machines are available in 2D or 3D models. 2-D models are used for engraving lettersor other designs, 3-D models are used for copying anyshape and contour of the work piece. The tracing stylusis moved manually on the contour of the model to beduplicated and the milling cutter mounted on the spindlemoves in a similar path on the work piece, reproducing theshape of the model.


Video9 10


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9,10

SPECIFICATIONS1. The max. length of longitudinal, cross and vertical travel


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of the table.

2. No. of spindle speeds,3. No. of table speeds and feeds4. Floor space required5. Net weight required6. Spindle nose taper (for vertical milling machine spindle

and horizontal milling machine arbors)


MILLING GEOMETRYPeripheral cutter: As the cutting edges are arranged radiallyon the periphery the rake angle is called radial rake which is


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on the periphery the rake angle is called radial rake which isthe cutting edges angle w.r.t to the periphery of the cutter. +ve

radial rake gives better performance in peripheral milling.Face cutter: Two rake angles are defined here.(a) Radial rake is the cutting insert’s angle w.r.t the peripheryof the cutter (b) Axial rake is the cutting insert’s angle w.r.t the central axisof the cutter.Axial Rake has significant effect on axial force and thrust

applied to the spindle. Radial rake has major effect ontangential and radial forces. +ve axial rake, - ve radial rakegives best performance.


PERIPHERAL CUTTER


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FACE CUTTER


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Side View

Bottom Vie w

METHODS OF MILLING1. Peripheral Milling: It is the operation performed by amilling cutter to produce a machined surface parallel to the


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milling cutter to produce a machined surface parallel to theaxis of rotation of the cutter. Here the cutting force is not

uniform throughout the length of cut by each tooth. Due tothis reason, a shock is developed in the mechanism of themachine that leads to a vibration. The quality of surfacegenerated and the shape of the chip formed is dependent

upon the rotation of the cutter relative to the direction of feedmovement of the work. According to the relative movement

between the tool and work, the peripheral milling isclassified into two types:



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(a) Up milling/ Conventional milling: The metal is removed by the cutter which is rotated against the travel of the W.P.The thickness of the chip is min. at the beginning of cut max.


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The thickness of the chip is min. at the beginning of cut max.when the cut terminates. The cutting force is directed up

wards and this tends to lift the work from the fixtures. Thisis used for roughing operations. The chips accumulate at the


cutting zone, andmay be carriedover with thecutter, spoilingthe work surface.It generates a poor finish. Cuttingforce and power are more.

(b) Down milling/ Climb milling: The metal is removed bythe cutter which is rotated in the same direction of travel of the W.P. The thickness of the chip is max. when the tooth


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the W.P. The thickness of the chip is max. when the tooth begins its cut and it reduces to the min. when the tooth

leave the work. The cutting force is directed down wards andthis tends seat the work firmly in the work holding devices.Hence fixture design is easier. This operation cannot be usedon old machine as the back lash error present in the screw

elements that may cause vibration and damages the work surface considerably. Hence this operation should be

performed on rigid machines provided with back lasteliminator. This is used for finishing operations. The chips

are also disposed off easily and do not interfere with thecutting. This results in improved surface finish. Cuttingforce and power are less.



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BACKLASH ELIMINATOR: This eliminates the backlash(play) between nut and table lead screw. Two independent nutsare mounted on lead screw. The nuts engage common crowngear which meshes with rack. The axial movement of rack is

controlled by the backlash eliminator, engaging a knob onfront of saddle. Turning the knob forces the nuts to movealong lead screw in opposite directions.

2. Face Milling: This is performed to produce a flatmachined surface to the axis of rotation of the cutter. In thisoperation both up milling and down milling may be


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operation both up milling and down milling may beconsidered to be performed simultaneously on the work

surface. When the cutter rotates through half of therevolution the direction of movement of the cutter tooth isopposite to the direction of feed and the condition reversewhen the cutter rotates through other half of revolution. The

chip thickness is min. at the beginning and at the end of thecut, and it is max. when the work passes through the centreline of cutter. The surface generated in face milling ischaracterized by the tooth circular marks of the cutter. Face

milling gives superior finish than peripheral milling.


Draw Bolt

S i dl


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Spindle

Cutter Holder

Spindle Nose Taper

3. End Milling: It is a combination of peripheral and facemilling operations. The cutter has cutting edges both on theend face and on the periphery. The cutting characteristics


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end face and on the periphery. The cutting characteristicsmay be of peripheral or face milling type according to the

particular cutter surface used. When end cutting edges areonly used to remove metal, the direction of rotation anddirection of cutters should be same. When peripheral cuttingedges are used, they must be opposite to each other.


Draw Bolt


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Collet Holder

End Mill

Collet

Collet Wrench

TAPER USED IN MILLING MACHINES

American Standard Taper of


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p3.5” per foot is made standard

taper in all milling machines built in U.S.

Brown and Sharpe Taper of 0.5” per foot is also widely used oncollets, end mills, arbors,milling machine spindles andgrinding machine spindles.

OPERATIONS1. Plain Milling : Producing plain, flat horizontal surface.

This is called slab milling if performed with a peripheral


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g p p pcutter and called face Milling if a face milling cutter is

used.

2. Side Milling: Producing flat vertical surface on the side of a work piece by using side milling cutter.


3. Straddle Milling: Producing flat vertical surfaces on bothsides of the work piece by using two side milling cutter mounted on the same arbor. The distance between the two


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cutter can be adjusted by using spacing collars.

4. Gang Milling: Machining several surfaces simultaneouslyusing a No. of cutters of same or diff. diameters mountedon the arbor of the machine, used widely for repetitive work


Video11

5. Form Milling: Producing irregular contours using formcutters like concave, convex or any other shape.


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6. End milling: Producing flat surfaces which may be vertical, horizontal or at an angle in reference t o

the table surface like slots, grooves, key ways,steps etc. A vertical milling machine is mostsuitable for end milling.

Convex Cutter

Concave Cutter

Convex Milling

Concave Milling

STEP 1 STEP 2

7. Saw milling: Producing narrow slots or grooves usingsaw milling cutter. It can also be performed for complete

parting off operation.


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8. Gear cutting: By using form relieved cutter having thesame profile of the tooth space of the gear.9. Helical Milling: Producing helical flutes or groovesaround the periphery of a cylindrical or conical work piece.

10. Cam Milling: Producing cams by using universal dividinghead and a vertical milling attachment. Note: 8, 9, 10, above can be done in indexing.

INDEXINGIt is the operation of dividing the periphery of a piece of work into any No. of equal parts. This is adopted for


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producing hexagonal and square headed bolts cutting

splines on shafts, flutes in milling cutters, drills, taps andreamers, cutting of Gears, cams etc. Indexing isaccomplished by using a special attachment known asdividing head or Index head. They are of 3 types

1) Plain / Simple dividing head 2) Universal Dividing head3) Optical Dividing headUsing these dividing heads, the work can be set in vertical,horizontal or in inclined positions relative to the tablesurface. There are several methods of indexing. The choiceof any one method depends upon the No. of divisionsrequired and the type of dividing head used.


PLAIN / SIMPLE INDEXING HEADS


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OPTICAL INDEXING HEADS


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METHODS OF INDEXING1) Direct Indexing: Also called rapid indexing, is usedmaking small No. of divisions. This can be performed in


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both plain and universal dividing head. The spindle and index

crank are connected by bevel gears. The required No. of divisions on the work is obtained by means of the rapid index

plate generally fitted to the front end of the spindle nose.The plate has 24 equally spaced holes, into any one of

which a spring loaded in is pushed to lock the spindle withthe frame. While indexing, the pin is first taken out and thenthe spindle is rotated by hand, and after the required

position is reached, it is again locked by pin. when the

plate is turned throughout the required part o a revolution,the dividing head spindle and the work are also turnedthrough the same part of the revolution.


With a rapid index plate having 24 holes, it is possible todivided the work into equal divisions of all factors of 24 i.e.2,3,4,6,8,12,24

Video


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Rule: No. of holes = No. of holes in the direct index plateto be moved No. of divisions reqd.

Q) Find out the index movement required to mill ahexagonal bolt by direct indexing.Ans. No. of holes to be moved = 24/6 = 4After machining one side of the bolt the index plate willhave to be moved by 4 holes for 5 times to machining theremaining 5 faces of the bolt.


Video12

2) Simple Indexing: Also called plain indexing, is moreaccurate and suitable for numbers beyond the range of rapidindexing. The bevel gears are replaced by a worm and worm


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wheel. The shaft carrying the crank has a single threaded

worm and it meshes with the worm wheel on spindle having40 teeth. 40 turns of crank are necessary to rotate the spindle


thro' one revolution,i.e one complete turn

of the index crank will cause the wormwheel to make 1/40of a revolution. For

indexing fractions of a turn, various index

plates are used.


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Q) Set the dividing headto mill 30 teeth on a spur wheel blank. Use 21 hole


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index plate.

Ans.Index crank movement= 40/30 = ==Thus for indexing, onecomplete turn and 7 holes


in 21 hole circle of the index plate will have to be moved by

the index crank, if 21 hole plate is selected. This can also be performed with 18 hole plate [ ] or 24 hole plate [ ]also.

Video 13

3) Compound indexing:- The indexing method is calledcompound due to the two separate movement of the indexcrank in two diff. hole circles of one (same) index plate to


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obtain a crank movement not obtainable by plain indexing.


4) Differential Indexing: The differential indexing may beconsidered as an automatic method of performingcompound indexing. Here the Index crank is connected to

milling machine feed rod through a set of gears to getcontinuous rotation for spindle for making helical grooves asshown.

Video14,15


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Setting of universal dividing head for spiral or helical grooves


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Setting of universal dividing head for spiral or helical grooves


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(i)

L = L 1 + AL + OT + 2∆


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(ii)

AL ∆L1

L = L 1 + AL + 2∆

AL OTL1

∆

∆∆

FRONT

VIEW

FRONTVIEW

(iii)L = L 1 + AL + ∆


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(iv)

d

AL OTL1

O

AB

C

L = L 1 + AL + OT

AL ∆L1

FRONTVIEW

FRONTVIEW

( ) M i hi hi k


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(v) Maximum uncut chip thickness =

(vi) Average uncut chip thickness =

(vii) Peak to valley height for surface roughness =

(viii) Effective no. of teeth cutting at same time =

(ix) Mean Tangential Force =F mt = K d f m W / πDNK = Material Constant(x) Mean Cutting Power = F mt V


i) Tool fully engaged, Roughing Pass – doesn’t require “Full Wipe”

b)For Face Cutters/End Mills


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q p

ii) Tool fully engaged, Finishing Pass – requires “Full Wiping ” (Single pass feed)

iii) Tool not fully engaged with W


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W/2

W O BA

C

AL = 0.5 cm OT = 0.5 cm

W

W/2

L1

L = L 1 + AL + OT + D

(i)

(ii)


A

TOPVIEW

TOPVIEW

AL OTL1

WA

(iii)


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O

AB

AL OTL1

W

AL = OT = D/2

(iv)

TOPVIEW

TOPVIEW

BROACHINGBroach is bar type cutter with series of cutting edgesgradually increasing in size to remove all materials in one


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stroke. In broaching there is only one motion, i.e. the primary cutting motion is provided by the machine, whereas the feed is obtained by placing the teeth progressivelydeeper. Since there is no feed motion, the shape of the

broach determines the shape of the machined part.Broach is used to produce internal forms like spline holes,non-circular holes, slots, grooves, gears etc. Internal

broaching is done by either pulling (or) pushing the broachthrough a hole drilled in the work piece. Pulling is highly

preferred to facilitate alignment and avoid buckling.


Video1,2

External forms can also be produced by using pot broach.Here the broach is made in segments and fixed inside afixture called pot fixture. The broach is stationary but the


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W.P. is pulled / pushed through it.


Internal broaches

Pot broach

GRINDINGIntroduction: Grinding is the process of removing excessmaterial by the abrasive action of a rotating wheel on thesurface of the work piece It is basically a finishing process


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surface of the work piece. It is basically a finishing process

employed to produce high accuracy and surface finish. Thegrinding wheel consists of sharp crystals called abrasivesheld together by suitable bonding. Natural abrasives availablein nature include sand stone (natural silica), diamond,

corundum and emery (natural alumina). Artificial abrasivesare free from impurities and possess better performance properties. They include Al 2O3, SiC, CBN etc.



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Natural Silica

White Al Oxide

Corundum Emery

SiC CBN

The various bonding materials used are:a) Vitrified bond (V) – It is made of clay and feldspar (rock forming mineral in earth’s crust). This is the strongest bond


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of all and is not effected by water/oils/acids. Vitrified bond is

suitable for high stock removal even at dry condition. Itcannot be used where mechanical impact or thermalvariations are likely to occur. This bond is also notrecommended for very high speed grinding because of

possible breakage of the bond under centrifugal force. b) Resinoid bond (B) – It is a synthetic thermosetting resin(phenolic resins) that becomes hard after heating. Thisoccupies next place to Vitrified bond. Conventional abrasiveresin bonded wheels are widely used for heavy duty grinding

because of their ability to withstand shock load.


c) Silicate bond (S) – It is made of sodium silicate and is usedfor operations that generate less heat.d) Rubber bond (R) – It is made of synthetic or natural


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rubber. Its principal use is in thin wheels for wet cut-off operation. They are denser than resinoid bonds but are lessheat resistant. Rubber bond was once popular for finishgrinding on bearings and cutting tools. They are also used for making regulating wheels in centreless grinding.e) Shellac bond (E) – This is also an organic bond and hasconsiderable strength. This not suitable for heavy duty work.At one time this bond was used for flexible cut off wheels. At

present use of shellac bond is limited to grinding wheelsengaged in fine finish of rolls.



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Vitrified Bond Resinoid Bond

Rubber BondParting Wheels

Shellac Bond

Silicate Bond

Rubber BondRegulating Wheels

Specification of Grinding WheelEg: 51 A 60 K 5 V 0551 – Manufacturer’s identification no. for exact kind of

abrasive used


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abrasive used

A – Type of abrasiveA – A l 2O3, B – CBN, C – SiC, D – Diamond60 – Average grit size or Mesh Size - 8-24 – Coarse;

30-60 – Medium; 80-180 – Fine; 220-600 – Very fine

K – Hardness of wheel (Bonding Strength)→A – Softest to Z – Hardest5 – Porosity of wheel → 1 to 15/20

1- Low porosity / Closed structure / More denser

15/20- High porosity / Open structure / Less denser V – Bonding material05 – Wheel manufacturer’s identifier


Classification of Grinding MachinesSurface Grinding M/c: Similar to Millinga) Horizontal Machine b) Vertical Machine

Video1,2,3,4


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Cylindrical Grinding M/c: Similar to lathe. Can perform bothExternal and Internal Grinding.Video

5


188/320



189/320


Centerless Grinding M/c: a) External MachineVideo

6,7


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Centerless Grinding M/c: b) Internal Machine


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192/320


EXTERNAL CENTRELESS GRINDING


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INTERNAL CENTRELESS GRINDING

Feeding System in External Machine1) Through feed is for step less small components like piston

pins, rollers of roller bearings, cam shafts, dowel pins.Here the regulating wheel rpm is less and also inclined


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Here the regulating wheel rpm is less and also inclined.

2) In feed / Plunge feed is for stepped components like Bolts,valve tappets etc. Stopper is provided.

3) End feed is for tapered components. Here the grindingwheel and regulating wheel are profiled to get the taper.


Special Grinding M/ca) Tool & Cutter grinder b) Thread Grinder


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Video8


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Video9,10

Different Dressers

Radius & Angular Dressing Attachment

Dressing: Dressing is the conditioning of the wheel surfacewhich ensures that grit cutting edges are exposed from the bond and thus will be able to penetrate into the work piecematerial and substantially influence the condition of the


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material and substantially influence the condition of the

grinding wheel.

Truing: Truing is the act of regenerating the requiredgeometry on the wheel. Truing is required whenever a new

wheel is loaded to ensure concentricity with machine spindle.It is done with a diamond truing tool by removing the outer layer and creating a concentric layer w.r.t the spindle axis.

Glazing: Glazing of the wheel is nothing but abrasive particles getting blunt. As they can be removed by dressing,grinding wheels are called self sharpening wheels.


Loading / Clogging: It is the condition when pores of thegrinding wheel get filled/clogged with chips. This can occur due to grinding of soft materials or by improper selection of grinding wheels or improper process parameters or improper


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grinding wheels or improper process parameters or improper

cutting fluids. Dressing will remove the clogged layer.


Note: 1.The specific energy requirement in Grinding(50 J/mm 3)is more than that required in turning (2 - 5 J/mm 3).This is because of the large contact area between the wheeland the work resulting due to the large no. of cutting edges.


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and the work resulting due to the large no. of cutting edges.

2. The Grinding wheels have random geometry. The rakeangle varies from +45 0 to -60 0 and more. The negative rakeincreases the cutting forces and promote rubbing actionaffecting the cutting action. Hence high rotational speeds are

used for minimizing the effect of negative rake.3. The ratio of thrust force to cutting force in Grinding is > 1.This is opposite in turning (i.e < 1).4. Soft wheels are used for hard materials as they break

easily to release worn out grains (High self sharpeningcapability). Hard wheels are used for soft materials as wear out is less and they retain the grains for more time.


5. GRINDING RATIO:• Grinding Ratio or G Ratio is the cubic mm of stock removed divided by the cubic mm of wheel lost.

• In conventional grinding it is 20:1 to 80:1


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In conventional grinding it is 20:1 to 80:1•

It is a measure of grinding production and reflects theamount of work a wheel can do during its useful life.• As the wheel loses material it must be reset to maintain the

required work piece size.

6. Al. oxide is the preferred abrasive compared to SiC togrind high tensile strength material like steel as Al. oxide istougher than SiC. Also Al. oxide shows higher chemicalinertness towards steel giving more wear resistance during

grinding.


Creep feed Grinding: It is differentfrom conventional grinding. Here theentire depth of cut is completed in one

pass only using very small feed rates


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p y g y

(0.005 mm/pass). High depth of cutsof order 1 to 30 mm with low speedsof 1 to 0.025 m/min are used. Cuttingforces and power required are more.

Open and soft wheels are used toaccommodate large volume of chipsgenerated. The cutting fluids are oil

based due to low grinding speeds. This


is mainly used for grinding work pieces made out of hardmaterials with deep slots or complex profiles and also for removing large amounts of material.Wheel wear rate is more.

SUPER FINISHING PROCESSESThe surface finish produced by various processes are:PROCESS: SURFACE FINISH (µm) : TYPE OF PROCESST i g b i g 0 05 t 25 M hi i g P


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Turning, boring : 0.05 to 25 : Machining ProcessMilling : 0.25 to 25 : Machining ProcessPlanning, shaping : 0.375 to 25 : Machining ProcessDrilling : 0.75 to 12.5 : Machining Process

Reaming, Broaching : 0.5 to 6.25 : Machining ProcessGrinding : 0.025 to 6.25 : Finishing ProcessHoning : 0.025 to 1.5 : Super Finishing ProcessLapping : 0.013 to 0.75: Super Finishing ProcessBurnishing : 0.01 to 0.25 : Super Finishing ProcessPolishing & Buffing: : Super Finishing Process


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