Singh R. Introduction to Basic Manufacturing Processes and Workshop Technology

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428 Introduction to Basic Manufacturing Processes and Workshop Technology

Drill axis is the longitudinal centre line.

Drill point is the sharpened end of the drill body consisting of all that part which is

shaped to produce lips, faces and chisel edge.

Lip or cutting edge is the edge formed by the intersection of the flank and face

Lip length is the minimum distance between the outer corner and the chisel-edge

corner of the lip.

Face is that portion of the flute surface adjacent to the lip on which the chip impinges

as it is cut from the work.

Chisel edge is the edge formed by the intersection of the flanks.

Flank is that surface on a drill point which extends behind the lip to the following flute.

Flutes are the grooves in the body of the drill, which provide lips, allow the removal of

chips, and permit cutting fluid to reach the lips.

Flute length is the axial length from the extreme end of the point to the termination

of the flutes at the shank end of the body.

Body is that portion of the drill nomenclature, which extends from the extreme cutting

end to the beginning of the shank.

Shank is that portion of the drill by which it is held and driven,

Heel is the edge formed by the intersection of the flute surface and the body clearance.

Body clearance is that portion of the body surface reduced in diameter to provide

diametric clearance.

Core or web is the central portion of the drill situated between the roots of the flutes

and extending from the point end towards the shank; the point end of the core forms the

chisel edge.

Lands are the cylindrically ground surfaces on the leading edges of the drill flutes. The

width of the land is measured at right angles to the flute.

Recess is the portion of the drill body between the flutes and the shank provided so as

to facilitate the grinding of the body. Parallel shank drills of small diameter are not usually

provided with a recess.

Outer corner is the corner formed by the intersection of the lip and the leading edge of

the land.

Chisel edge comer is the corner formed by the intersection of a lip and the chisel edge.

Drill diameter is the measurement across the cylindrical lands at the outer corners of

the drill. .

Lead of helix is the distance measured parallel to the drill axis between corresponding

points on the leading edge of a flute in one complete turn of the flute.

Helix angle is the angle between the leading edge of the land and the drill axis.

Rake angle is the angle between the face and a line parallel to the drill axis. It is bigger

at the face edges and decreases towards the center of the drill to nearly 0°. The result is that

the formation of chips grows more un-favorable towards the centre.

Lip clearance angle is the angle formed by the flank and a plane at right angles to the

drill axis; the angle is normally measured at the periphery of the drill. To make sure that

Drilling Machine 429

the main cutting edges can enter into the material, the clearance faces slope backwards in

a curve. The clearance angle is measured at the face edge, must amount to 5° up to 8°.

Point angle is the included angle of the cone formed by the lips.

Overall len

Neck

Bod

Shank

Helix an

Flute len

Lead or helix

Flute

Heel

Land

Axis

Tan

Cuttin

portion

Diameter

Bod

clearance dia.

Land

Chisel

Web or core

thickness

Depth or bod

clearance

Lip clearance

Chisel ed

corner

Lip

len

Outer corner

Relative lip

hei

Face

Lip

Dia.

Flank

Point

Helix an

at peripher

Enlar

ed view of

clearance at a

Top rake

Cuttin

Front

clearance

Enlar

sec X - X

Outer corner

Fig. 22.5 Geometry and nomenclature of twist drill

22.4.2 Drill Material

Drills are made are made up of high speed steel. High speed steel is used for about 90

per cent of all twist drills. For metals more difficult to cut, HSS alloys of high cobalt series

are used.

22.5 OPERATIONS PERFORMED ON DRILLING MACHINE

A drill machine is versatile machine tool. A number of operations can be performed on

it. Some of the operations that can be performed on drilling machines are:

430 Introduction to Basic Manufacturing Processes and Workshop Technology

1. Drilling 2. Reaming

3. Boring 4. Counter boring

5. Countersinking 6. Spot facing

7. Tapping 8. Lapping

9. Grinding 10. Trepanning.

The operations that are commonly performed on drilling machines are drilling, reaming,

lapping, boring, counter-boring, counter-sinking, spot facing, and tapping. These operations

are discussed as under.

22.5.1 Drilling

This is the operation of making a circular hole by

removing a volume of metal from the job by a rotating

cutting tool called drill as shown in Fig. 22.6. Drilling

removes solid metal from the job to produce a circular

hole. Before drilling, the hole is located by drawing two

lines at right angle and a center punch is used to make an

indentation for the drill point at the center to help the drill

in getting started. A suitable drill is held in the drill

machine and the drill machine is adjusted to operate at

the correct cutting speed. The drill machine is started and

the drill starts rotating. Cutting fluid is made to flow liberally

and the cut is started. The rotating drill is made to feed

into the job. The hole, depending upon its length, may be

drilled in one or more steps. After the drilling operation is

complete, the drill is removed from the hole and the power

is turned off.

22.5.2 Reaming

This is the operation of sizing and finishing a hole

already made by a drill. Reaming is performed by means

of a cutting tool called reamer as shown in Fig. 22.7.

Reaming operation serves to make the hole smooth,

straight and accurate in diameter. Reaming operation is

performed by means of a multitooth tool called reamer.

Reamer possesses several cutting edges on outer periphery

and may be classified as solid reamer and adjustable

reamer.

22.5.3 Boring

Fig. 22.8 shows the boring operation where enlarging

a hole by means of adjustable cutting tools with only one

cutting edge is accomplished. A boring tool is employed

for this purpose.

Work stationar

Reamer rotates

Fig. 22.7 Reaming operation

Drill feeds

and rotates

Work stationar

Fig. 22.6 Drilling operation

Tool feeds

Work rotates

Fig. 22.8 Boring operation

Drilling Machine 431

22.5.4 Counter-Boring

Counter boring operation is shown in Fig. 22.9. It is

the operation of enlarging the end of a hole cylindrically,

as for the recess for a counter-sunk rivet. The tool used is

known as counter-bore.

22.5.5 Counter-Sinking

Counter-sinking operation is shown in Fig. 22.10. This is the operation of making a cone-

shaped enlargement of the end of a hole, as for the recess for a flat head screw. This is done

for providing a seat for counter sunk heads of the screws so that the latter may flush with

the main surface of the work.

78°

(a)

(b)

Fig. 22.10 Counter sinking operation

22.5.6 Lapping

This is the operation of sizing and finishing a hole by removing very small amounts of

material by means of an abrasive. The abrasive material is kept in contact with the sides of

a hole that is to be lapped, by the use of a lapping tool.

22.5.7 Spot-Facing

This is the operation of removing enough material to provide a flat surface around a hole

to accommodate the head of a bolt or a nut. A spot-facing tool is very nearly similar to the

counter-bore

22.5.8 Tapping

It is the operation of cutting internal threads by using a

tool called a tap. A tap is similar to a bolt with accurate threads

cut on it. To perform the tapping operation, a tap is screwed

into the hole by hand or by machine. The tap removes metal

and cuts internal threads, which will fit into external threads

of the same size. For all materials except cast iron, a little

lubricate oil is applied to improve the action. The tap is

not turned continuously, but after every half turn, it should be

Fig. 22.9 Counter boring

operation

Fig. 22.11 Tapping operation

432 Introduction to Basic Manufacturing Processes and Workshop Technology

reversed slightly to clear the threads. Tapping operation is shown in Fig.22.11. The geometry

and nomenclature of a tap is given in Fig. 22.12.

Overall len

Shank len

Thread len

Chamfer

Len

th of

square

Drivin

centre

Shank dia

External

centre

Internal

centre

Point

dia

Web

die

Size of source

Axis

Cuttin

Heel

Unrelieved

land

Relived

Positive

Rack an

Land

ative

rake

Pitch

Flank

Basic hei

ht of thread

Max. Tap

major

Min.Tap

major

dia

Basic

major

dia

Relieved to

cuttin

Basic

minor dia

Basic

effective

dia

Flute

Chamfer

relief

Cutter

Heel

Face

Fig. 22.12 Geometry and nomenclature of tap

22.5.9 Core drilling

Core drilling operation is shown in Fig. 22.13. It is a main

operation, which is performed on radial drilling machine for

producing a circular hole, which is deep in the solid metal by

means of revolving tool called drill.

22.6 SIZE OF A DRILLING MACHINE

Different parameters are being considered for different

types of drilling machines to determine their size. The size of

a portable drilling machine is decided by the maximum diameter

of the drill that it can hold. The sensitive and upright drilling

machines are specified by the diameter of the largest workpiece which can be centered under

the drill machine spindle. A radial drilling machine is specified by the length of the arm and

the diameter of the column. To specify a drilling machine completely, following other parameters

may also be needed:

1. Table diameter

2. Number of spindle speeds and feeds available

3. Maximum spindle travel

4. Morse taper number of the drill spindle

5. Power input

6. Net weight of the machine

7. Floor space required, etc.

Fig. 22.13 Core drilling

operation

Drilling Machine 433

22.7 CUTTING SPEED

The cutting speed in a drilling operation refers to the peripheral speed of a point on the

surface of the drill in contact with the work. It is usually expressed in meters/min. The

cutting speed (C

) may be calculated as:

= ((22/7) × D × N)/1000

Where, D is the diameter of the drill in mm and

N is the rpm of the drill spindle.

22.8 FEED

The feed of a drill is the distance the drill moves into the job at each revolution of the

spindle. It is expressed in millimeter. The feed may also be expressed as feed per minute. The

feed per minute may be defined as the axial distance moved by the drill into the work per

minute. The feed per minute may be calculated as:

F = F

× N

Where, F = Feed per minute in mm.

= Feed per revolution in mm.

N = R.P.M. of the drill.

22.9 QUESTIONS

1. State the working principle of a drilling machine.

2. Explain principal parts of the drilling machine and sketch the mechanism of a drilling

machine.

3. Give the classification of drilling machines.

4. How will you specify a drilling machine?

5. What operations can be done on a drilling machine? Discuss them with diagrams.

6. With the help of a line diagram, describe the construction of radial drilling machine.

7. List the devices commonly used for holding the work on a drilling machine, and describe any three.

8. Define cutting speed, feed and machining time for drilling.

9. Sketch a twist drill and name its different parts.

10. What is boring? Sketch a boring tool.

11. What is the function of flutes on a twist drill bit? Why are straight flute drills used for non-

ferrous materials and metal?

12. Draw suitable figure for a drill bit showing:

(i) point (ii) lip clearance (iii) point angle (iv) flute (v) margin and (vi) body clearance

13 Write short notes on following:

(i) Drilling (ii) Boring, (iii) Reaming (iv) Tapping (v) Counter boring (vi) Counter sinking

14. Explain various types of operations performed on a drilling machine by neat sketches.

15. Define the following terms used in drilling operation.

(i) Cutting speed (ii) Feed

434 Introduction to Basic Manufacturing Processes and Workshop Technology

434

SHAPER, PLANER AND SLOTTER

23.1 SHAPER

Shaper is a reciprocating type of machine tool in which the ram moves the cutting tool

backwards and forwards in a straight line. The basic components of shaper are shown in

Fig. 23.1. It is intended primarily to produce flat surfaces. These surfaces may be horizontal,

vertical, or inclined. In general, the shaper can produce any surface composed of straight-line

elements. The principal of shaping operation is shown in Fig. 23.2 (a, b). Modern shapers can

also generate contoured surface as shown in Fig. 23.3. A shaper is used to generate flat

(plane) surfaces by means of a single point cutting tool similar to a lathe tool.

Column

Table

Base

Vice

Job

Tool

Toolhead

Ram

Fig. 23.1 Principal components of a shaper

23.2 WORKING PRINCIPLE OF SHAPER

A single point cutting tool is held in the tool holder, which is mounted on the ram. The

workpiece is rigidly held in a vice or clamped directly on the table. The table may be

supported at the outer end. The ram reciprocates and thus cutting tool held in tool holder

moves forward and backward over the workpiece. In a standard shaper, cutting of material

CHAPTER

Shaper, Planer and Slotter 435

takes place during the forward stroke of the ram. The backward stroke remains idle and no

cutting takes place during this stroke. The feed is given to the workpiece and depth of cut

is adjusted by moving the tool downward towards the workpiece. The time taken during the

idle stroke is less as compared to forward cutting stroke and this is obtained by quick return

mechanism. The cutting action and functioning of clapper box is shown in Fig.23.4 during

forward and return stroke.

Job feeds laterall

Tool reciprocates

Shapin

A’

B’

Tool

(a)

(b)

Fig. 23.2 (a, b) Working principal of shaping machine

(a) Grooved block

(b) Dove tail slide

(d) V-Block

Surface produced b

a shaper

Fig. 23.3 Job surfaces generated by shaper

Tool

Clapper box

Chip

Tool cleared

from machined

surface

Lifted clapper

box

(a) Forward stroke

(b) Return stroke

Job

Fig. 23.4 Cutting action and functioning of clapper box

436 Introduction to Basic Manufacturing Processes and Workshop Technology

23.3 TYPES OF SHAPERS

Shapers are classified under the following headings:

(1) According to the type of mechanism used for giving reciprocating motion to the ram

(a) Crank type

(b) Geared type

(2) According to the type of design of the table:

(a) Standard shaper

(b) Universal shaper

(3) According to the position and travel of ram:

(a) Horizontal type

(b) Vertical type

(4) According to the type of cutting stroke:

(a) Push type

(b) Draw type.

A brief description these shapers is given below-

23.3.1 Crank Shaper

This is the most common type of shaper. It employs a crank mechanism to change

circular motion of a large gear called “bull gear” incorporated in the machine to reciprocating

motion of the ram. The bull gear receives power either from an individual motor or from an

overhead line shaft if it is a belt-driven shaper.

23.3.2 Geared Shaper

Geared shaper uses rack and pinion arrangement to obtain reciprocating motion of the

ram. Presently this type of shaper is not very widely used.

23.3.3 Hydraulic Shaper

In hydraulic shaper, reciprocating motion of the ram is obtained by hydraulic power. For

generation of hydraulic power, oil under high pressure is pumped into the operating cylinder

fitted with piston. The piston end is connected to the ram through piston rod. The high

pressure oil causes the piston to reciprocate and this reciprocating motion is transferred to

the ram of shaper. The important advantage of this type of shaper is that the cutting speed

and force of the ram drive are constant from the very beginning to the end of the cut.

23.3.4 Standard Shaper

In standard shaper, the table has only two movements, horizontal and vertical, to give

the feed.

23.3.5 Universal Shaper

A universal shaper is mostly used in tool room work. In this type of shaper, in addition

to the horizontal and vertical movements, the table can be swiveled about an axis parallel to

Shaper, Planer and Slotter 437

the ram ways, and the upper portion of the table can be tilted about a second horizontal axis

perpendicular to the first axis.

23.3.6 Horizontal Shaper

In this type of shaper, the ram holding the tool reciprocates in a horizontal axis.

23.3.7 Vertical Shaper

In vertical shaper, the ram reciprocates in a vertical axis. These shapers are mainly used

for machining keyways, slots or grooves, and internal surfaces.

23.3.8 Travelling Head Shaper

In this type of shaper, the ram while it reciprocates, also moves crosswise to give the

required feed.

23.3.9 Push Type Shaper

This is the most general type of shaper used in common practice, in which the metal is

removed when the ram moves away from the column, i.e. pushes the work.

23.3.10 Draw Type Shaper

In this type of shaper, the cutting of metal takes place when the ram moves towards the

column of the machine, i.e. draws the work towards the machine. The tool is set in a reversed

direction to that of a standard shaper.

23.4 PRINCIPAL PARTS OF SHAPER

Fig. 23.5 shows the parts of a standard shaper. The main parts are given as under.

1. Base

2. Column

3. Cross-rail

4. Saddle

5. Table

6. Ram

7. Tool head

8. Clapper box

9. Apron clamping bolt

10. Down feed hand wheel

11. Swivel base degree graduations

12. Position of stroke adjustment hand wheel

13. Ram block locking handle

14. Driving pulley

15. Feed disc

16. Pawl mechanism

17. Elevating screw

Some of important parts are discussed as under.