Drilling and boring

UNIT-III(B)

DRILLING AND BORING MACHINES

By D. Kanaka Raja

Department of mechanical engineering,AITS

Drilling is the operation of producing circular hole in the work-piece by using a rotating cutter called DRILL.

The machine used for drilling is called drilling machine.

The drilling operation can also be accomplished in lathe, in which the drill is held in tailstock and the work is held by the chuck.

The most common drill used is the twist drill.

It is the simplest and accurate machine used in production shop.

DRILLING

DRILLING MACHINE

Drilling machine Spindle

Turns drill to advance into work (hand or automatically) Work table

Holds workpiece rigidly in place as hole drilled Used primarily to produce holes in metal Other operations: tapping, reaming, boring, counter

boring, countersinking, spot-facing

WORKING PRINCIPAL OF DRILLING MACHINE

The rotating edge of the drill exerts a large force on the workpiece and the hole is generated.

The removal of metal in a drilling operation is by shearing and extrusion.

SPECIFICATIONS OF DRILLING MACHINE

Size of drilling table. Largest bit the machine can held. Maximum size of the hole that can be drilled. Maximum size the work piece that can be

held. Power of the motor, spindle speed or feed.

TOOL NOMENCLATURE

TYPES OF DRILLING MACHINESa) Based on construction: Portable, Sensitive or bench drilling machine Radial, up-right, Gang, Multi-spindle Automatic Turret Deep hole b)Based on Feed:

Hand and Power driven Portable drilling machine

PORTABLE DRILLING MACHINE

It is a small light weight, compact and self contained unit that can drill holes upto 12.5 mm diameter.

The machine is driven by a small electric motor operating at high speed.

The machine is capable

of drilling holes in the workpieces in any position.

SENSITIVE OR BENCH DRILLING MACHINE

These are light duty vehicles. Mounted on benches. To drill small diameter holes ,a

twist drill is fitted in the drill chuck. This design is used to drill hole

from 1.5mm to 15mm diameter. The controls are light and delicate

speeds from 800 to 900 rpm are typical range.

SENSITIVE DRILLING MACHINE

DRIVE MECHANISM IN SENSITIVE DM

UP-RIGHT DRILLING MACHINE

Similar to sensitive drills have power feed mechanism for rotating drills and are designed for heavier.

It is used for heavier work. Drill holes upto 50mm

Table can move vertically and radially

UP-RIGHT DRILLING MACHINE

RADIAL DRILLING MACHINE

It the largest and most versatile used fro drilling medium to large and heavy work pieces.

It can be radially adjusted around the column in any position over the work to get different size and shapes of work.

The moments may be either manual or power driven.

The table is to be rotated through 360 deg.

The wide rang of power are as well as sensitive and geared manual feeds.


This machine is used for drilling medium to large heavy work pieces.

Types of radial drilling machine. 1) plain radial drilling machine 2) semi universal drilling machine 3) universal drilling machine

DRIVE IN RDM

GANG DRILLING MACHINE When drilling spindles are mounted

on a single table, it is known as a gang drill.

Each of these spindles can be independently set for different speed and depth of cut.

Such machines are useful when number of holes of different sizes are to be drilled on the same work piece.

Apart from drilling, a number of other machining operations like reaming counter boring, tapping etc can also be performed at a time on this machine.

GANG DRILLING MACHINE

TURRET TYPE DRILLING MACHINE The stations are set up with

a variety of tools numerical control is a also available.

Two fixtures can be located side by on the workable table, thus permitting loading and unloading of one part while the other part is being machined this reduces the machine cycle.

TURRET TYPE DRILLING MACHINE

DEEP HOLE DRILLING These machines are used for drilling

holes whose depth exceed normal drill size. These machines are operated at high speed and low feed.

These machines are either horizontal or vertical. The work or the drill may revolve. most machines are of horizontal construction using a center cut gun drill, which has a single cutting edge with a straight flute running througout its length.

These machines are very useful for drilling deep holes in rifle travels, crankshafts.

DEEP HOLE DM

DEEP HOLE DRILLING MACHINE

Very deep holes of L/D ratio 6 to even 30, required for rifle barrels,

long spindles, oil holes in shafts, bearings, connecting rods etc, are

very difficult to make for slenderness of the drills and difficulties in

cutting fluid application and chip removal.

Such drilling cannot be done in ordinary drilling machines and

bordinary drills.

It needs machines like deep hole drilling machine such as gun drilling

machines with horizontal axis which are provided with

DRILLING OPERATIONS…

Operations that can be performed in a drilling machine are

Drilling Reaming Boring Counter boring Countersinking Tapping and Spot Facing

DRILLING OPERATIONS…

OPERATIONS PERFORMED

Drilling Operation of producing hole by

removing metal from solid massusing twist drill

• Countersinking– Operation of producing tapered

or cone-shaped enlargementto end of hole


ReamingOperation of sizing and producing

smooth, round hole from previouslydrilled or bored hole

• Boring• Truing and enlarging hole by

means of single-point cutting tool


TappingCutting internal threads in hole

with cutting tool called tap

• Counterboring– Enlarging top of previously

drilled hole to given depthto provide square shoulder for head of bolt or capscrew

OPERATIONS IN DRILLING MACHINE

COUNTER BORE AND SPOT FACING

OPERATIONS IN DRILLING MACHINE

TOOL HOLDING DEVICES

Tool-holding devices are Used to hold or drive cutting tool The different methods used for holding drill in a drill spindle

are By directly fitting in the spindle hole. By using drill sleeve By using drill socket By using drill chuck

TOOL-HOLDING DEVICES

Drill press spindle provides means of holding and driving cutting tool

End may be tapered or threaded for mounting drill chuck

Most commonDrill chucksDrill sleevesDrill sockets

DRILL FIXED TO THE SPINDLE

Drilling operations

Drilling Centre HoleDrilling Deep HolesDrilling Thin MaterialDrilling Pilot Hole

DRILL CHUCKS

Most common devices used for holding straight-shank cutting tools

Most contain three jaws that move simultaneously when outer sleeve turned Hold straight shank of cutting tool securely

Two common types Key Keyless

WORK HOLDING DEVICES

CHUCKS

Hold straight-shank drills Mounted on drill press spindle

Taper

– Threads• Held in spindle by self-holding

taper in larger machines• Four types of drill chucks

TYPES OF DRILL CHUCKS

Key-type Most common Three jaws move simultaneously

when outer sleeve turned Tighten with key

Keyless Chuck loosened or tightened by

hand without key Precision keyless

Holds smaller drills accurately

DRILL CHUCKS

TOOL HOLDER

DRILL TYPES

TYPES OF CUTTERS

Reamers :-Multi tooth cutting toolAccurate way of sizing and finishing the pre-existing hole. Accuracy of 0.005mm can be achieved

Boring Tool:-Single point cutting tool.Boring tool is held in the boring bar which has the shank.Accuracy of 0.005mm can be achieved.

TYPES OF CUTTERS

Countersinks :-Special angled cone shaped enlargement at the end of the hole Cutting edges at the end of conical surface.Cone angles of 60°, 82°, 90°, 100°, 110°, 120°

Counter Bore Tool:-Special cutters uses a pilot to guide the cutting action .Accommodates the heads of bolts.

TYPES OF CUTTERSCombined Countersinks and central drill :-

Special drilling tool to start the hole accurately.At the end it makes countersinks in the work piece.

Gun drill :-Machining of lengthy holes with less feed rates.To overcome the heating and short life of the normal drill tool

TYPES OF CUTTERS

Tapping:- For cutting internal

thread Multi cutting edge

tool. Tapping is performed

either by hand or by machine.

Minor dia of the thread is drilled and then tapping is done.

Drilling And Drills

Types of drills– Twist drill: most

common drill– Step drill:

produces holes of two or more different diameters

– Core drill: used to make an existing hole bigger


1. Machine Table Vice

Step Blocks Clamps V-Blocks Angles Jigs T- Slots Bolt


DRILL MATERIALS

The two most common types are1. HSS drill

- Low cost2. Carbide- tipped drills

- high production and in CNC machines

Other types areSolid Carbide drill, TiN coated drills, carbide coated masonry drills, parabolic drills, split point drill

GRINDING OF DRILLS

PARAMETERS DEFINITIONS Cutting Speed (v):-

It’s the peripheral speed of the drillv = *D*N whereD = dia of the drill in mN = Speed of rotation in rpm

Feed Rate (f):-It’s the movement of drill along the axis (rpm)

Depth of Cut (d):-The distance from the machined surface to the drill axis

d = D / 2

Material Removal Rate:-It’s the volume of material removed by the drill per unit time

MRR = ( D2 / 4) * f * N mm3 / min

Machining Time (T) :-It depends upon the length (l) of the hole to be drilled , to the Speed (N) and feed (f) of the drill

t = L / f N min

REAMING

86

WHAT IS MEANT BY BORING?

Boring is the process of

enlarging an existing drilled

holes with a single point cutting

tool.

Boring operation can be

performed on engine lathe

Fig.1

CLASSIFICATION OF BORING MACHINE Horizontal boring machine ( production

machines)i. Table type HBMii. Planer type HBMiii. Floor type HBM

Vertical boring machine( production machines)

Jig boring machine

HORIZONTAL BORING MACHINE

HORIZONTAL BORING MACHINE The table type or universal type is the most versatile and

commonly used horizontal boring machine. Bed a heavy and strong bed carries the entire load of different

parts, work piece and tool over it. Columns a two vertical columns, one on each end of the table. Head stock the head stock can be moved vertically along the

main column. Load bearing end support it supports the end of a long boring

bar and can be adjusted vertically along the end support column. Horizontal table it is mounted on a saddle and can be moved

horizontal forward and backward and side by moving the saddle.

HORIZONTAL BORING MACHINE

VERTICAL BORING MACHINE

VERTICAL BORING MACHINE The parts whose length or height is than diameter are

machined. The work is fastened on a horizontal revolving table and the

cutting tool or tools which are stationary , advance vertically into it as the revolves.

Horizontal cross rail is carried on vertical sideways and carries the tool holder slide or slides.

Most machine also have a slide tool head. Vertical boring machine is sometimes called a rotary planer

and its cutting action on flat disc is identical with a planer. These machines rated according to their table diameter, vary

in size from 0.9 to 12m.

FLOOR TYPE BORING MACHINE

PLANER TYPE BM

MULTIPLE HEAD BM

TURRET TYPE BM

JIG BORING MACHINE

Jig boring machine resembles in

appearance to a vertical milling machine.

Rugged enough for heavy cuts and

sensitive enough for light cuts. Essential for modern mass production

The machining accuracy of jig boring

machine is very high, within a range of

0.0025 mm.

101

NEED OF JIG BORING MACHINE

Jig boring machines are mainly to perform machining operations like• Boring. • Drilling. • Reaming.• Counter boring holes in metal jigs • Counter-sinking holes in metal work pieces.

Some jig boring machines are used for accurately enlarging the • Existing holes. • Making their diameters highly accurate Boring can correct hole location, size, or alignment and

can produce a good finish if a fine feed and correct tool are used.

102

NEED OF JIG BORING MACHINE

Jig boring can also maintain high accuracy between multiple holes or holes and surfaces.

Some jig boring machines are designed to machine holes with the tightest tolerances possible with a machine tool.

The constant demand for accuracy within many branches

of metalworking has been fulfilled with the help of applications possible by jig-boring machines.

JIG BORING MACHINE

Jig boring machines are used in precision tool room applications for locating and

boring holes in

• Jigs.

• Fixtures.

• Gauges.

• And other precision parts.

To prevent the influence of ambient temperature on machining accuracy

Jig boring machines should be installed in a special environmental enclosures (i.e.,

in a temperature controlled rooms) with temperature maintained at a level of 20

°C.

Jig borers can be used as coordinate measuring machine for inspection and

precision layout operation .103

Simple Jig Boring Machine

columnspindle head

quill

boring toolspindle

table

bedsaddle

Line DiagramFig.2

PARTS OF JIG BORING MACHINE

JIG BORING MACHINE

105

Fig.3

JIG BORING MACHINE

The main distinguishing features of these machines are : The spindle and other parts are rigid to prevent deflection.

The spindle runs in preloaded ant frictional bearings.

The spindle housing is made of material having very low co-efficient of linear

expansion .

For boring, the work pieces are clamped on the table by T-bolts and straps.

an existing hole is enlarged by using a single point tool.

The single point tool produces

• Better surface finish.

• And locates holes with maximum accuracy. 106

JIG BORING MACHINE

⎯ high spindle speed ⎯ high rigidity ⎯ tool guide ⎯ Pressurized cutting oil for effective cooling, chip

removal and lubrication at the drill tip. Deep hole drilling machines are available with both

hard automation and CNC system.

JIG BORING MACHINE

The principle of boring using single point tool is illustrated

in fig.

108

Fig.4

PARTS OF JIG BORING MACHINE

CUTTING FORCES

KINEMATIC SYSTEM OF GENERAL PURPOSE DRILLING MACHINE AND THEIR PRINCIPLE OF WORKING

KINEMATIC SYSTEM OF GENERAL PURPOSE DRILLING MACHINE AND THEIR PRINCIPLE OF

WORKING

Mechanisms to enable transform and transmit motion(s) from the power source(s) to the cutting tool and the workpiece for the desired machining action.

a typical kinematic system of a very general purpose drilling machine, i.e., a column drilling machine having 12 spindle speeds and 6 feeds.

The kinematic system enables the drilling machine the following essential works;


WORKING Cutting motion: The cutting motion in drilling machines is attained by rotating the drill at

different speeds (r.p.m.).

Like centre lathes, milling machines etc, drilling machines also need to have a reasonably large number of spindle speeds to cover the useful ranges of work material, tool material, drill diameter, machining and machine tool conditions.

The drill gets its rotary motion from the motor through the speed gear box (SGB) and a pair of bevel gears.

For the same motor speed, the drill speed can be changed to any of the 12 speeds by shifting the cluster gears in the SGB. The direction of rotation of the drill can be changed, if needed, by operating the clutch in the speed reversal mechanism, RM-s shown in the figure.


WORKING Feed motion In drilling machines, generally both the cutting motion and feed

motion are imparted to the drill. Like cutting velocity or speed, the feed (rate) also needs varying (within a range) depending upon the tool-work materials and other conditions and requirements.

drill receives its feed motion from the output shaft of the SGB through the feed gear box (FGA), and the clutch. The feed rate can be changed to any of the 6 rates by shifting the gears in the FGB. And the automatic feed direction can be reversed, when required, by operating the speed reversal mechanism, RM-s as shown

Tool work mounting The taper shank drills are fitted into the taper hole of the

spindle either directly or through taper socket(s). Small straight shank drills are fitted through a drill chuck

having taper shank. The work piece is kept rigidly fixed on the bed (of the table). Small jobs are generally held in vice and large or odd

shaped jobs are directly mounted on the bed by clamping tools using the T-slots made in the top and side surfaces of the bed as indicated


WORKING

Drilling and boring

Engineering

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