Turning Workpiece (Basic)

Worksheet 2.2.2: Grinding tool bit
Answer key:

Face

Flank Base
Side Cutting Edge
Front
Cutting Edge Flank

Nose

Code No. Turn workpiece Date: Developed Date: Revised Page #
MEE722302 2

Information Sheet 3.1.1: Properties of materials
Learning outcomes:
1 Turn workpiece
Learning Activity:
1.1 Identify classification of material
Mechanical Properties of Metals
Properties of metals refer to the way metals behave when acted upon by external forces.
Properties of Engineering Materials
Ductility
It is the ability of a metal to be permanently deformed without breaking.

Tensile Strength
The maximum amount of pull that a metal can withstand before breaking.

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 1

Information Sheet 3.1.1: Properties of materials

Compressive Strength
It is the ability of a metal to withstand heavy compressive (pressing) forces.

Hardness
It is the ability of a metal to resist penetration by force.

Toughness
It is the property of a metal to withstand shock or impact.

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 3.1.1: Properties of materials

Malleability
It is the property of a metal which allows it to be hammered or rolled into shapes.

Brittleness
It is the property of a metal which does not allow permanent distortion before breaking

Machinability
It describes how easily or difficult a material can be machined. Some of the factors that affect
machinability are:

• Type of tool material used
• Type of work material used
• Shape of tool
• Hardness of work material
• Shape and size of work

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 3

Information Sheet 3.1.1: Properties of materials

Ferrous and Non-Ferrous Metals

 Ferrous Metals
They are metals or alloys which contain iron.
Mild steel, high-carbon steel, high-speed steel, stainless steel and cast iron are ferrous metals

 Non-Ferrous Metals
They are metals or alloys which do not contain iron.
Copper, brass, bronze, aluminium, tin and zinc are non-ferrous metals.

Types of Iron
Pig Iron

 It is the first product from iron ore.
 It contains impurities
 It is used for making steel and casting.

Cast Iron
 It is remelted pig iron with carbon added.
 Lathe beds and milling machine tables are made of cast iron.

Wrought Iron

 It is basically purified pig iron with a very low carbon content.
 It is tough and malleable
 It can be easily formed into any shape in the cold state

Wrought Iron

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 3.1.1: Properties of materials
Generally, it is used for making ornamental objects, eg. gates and fencing.

Plain Carbon Steel
 Basically, it is made of iron and carbon without major alloying elements.
 It is classified according to the carbon content in the steel.

Classification and Uses of Plain Carbon Steel

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 3.1.1: Properties of materials
Classification and Uses of Plain Carbon Steel

Characteristics and Uses of Common Non-Ferrous Metals

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 6

Information Sheet 3.1.1: Properties of materials
Characteristics and Uses of Common Non-Ferrous Metals

Alloys

 An alloy is a mixture of two or more metals.

 Alloying is used to produce a metal by mixing a base material. (e.g. carbon steel)

with smaller amounts of other metals (e.g. Tungsten, nickel and chromium)

Purpose of Alloying

Adding alloying elements may change one or more of the following properties to steel:
• Increase tensile strength
• Increase hardness
• Increase wear-resistance
• Increase rust-resistance
• Impart red hardness
• Improve machinability

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 3.1.1: Properties of materials
Effects of Alloying Elements on Steel

Characteristics and Uses of Common Non- Ferrous Alloys

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 8

Information Sheet 3.1.1: Properties of materials
Characteristics and Uses of Common Non- Ferrous Alloys

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 9

Worksheet 3.1.2: Classification of Engineering Materials

Learning outcomes:
1 Turn Workpiece
Learning Activity:
1.1 Objectives

At the end of the lesson, student should be able to:
1. Identify the properties of engineering materials.
2. Differentiate ferrous and non-ferrous materials.
3. Identify types of iron and their uses.

Test Your Self

Direction: Select the best answer.

1. It is the ability of a metal to be permanently deformed without breaking.

a) Ductility
b) Tensile Strength
c) Comprehensive Strength
d) Hardness

2. The maximum amount of pull that a metal can withstand before breaking.

a) Ductility
b) Tensile Strength
c) Comprehensive Strength
d) Hardness

3. It is the ability of a metal to withstand heavy compressive (pressing) forces.

a) Ductility
b) Tensile Strength
c) Comprehensive Strength
d) Hardness

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 1

Worksheet 3.1.2: Classification of Engineering Materials

4. It is the ability of a metal to resist penetration by force.

a) Ductility
b) Tensile Strength
c) Comprehensive Strength
d) Hardness

5. It is the property of a metal to withstand shock or impact.

a) Ductility
b) Toughness
c) Comprehensive Strength
d) Hardness

6. It is the property of a metal which allows it to be hammered or rolled into shapes.

a) Ductility
b) Malleability
c) Comprehensive Strength
d) Hardness

7. It is the property of a metal which does not allow permanent distortion before breaking.

a) Ductility
b) Toughness
c) Brittleness
d) Hardness

8. Basically, it is made of iron and carbon without major alloying elements.

a) Pig iron
b) Wrought
c) Cast iron
d) Plain Carbon steel

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 2

Worksheet 3.1.2: Classification of Engineering Materials

9. It is basically purified pig iron with very low carbon content.

a) Pig iron
b) Wrought iron
c) Cast iron
d) Plain Carbon steel

10. It is remelted pig iron with carbon added

a) Pig iron
b) Wrought
c) Cast iron
d) Plain Carbon steel

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 3

Worksheet 3.1.2: Classification of Engineering Materials

Answer Key:

1. A
2. B
3. C
4. D
5. B
6. B
7. C
8. D
9. B
10. C

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 4

Information Sheet 3.2.1: Lathe types, specifications, parts and functions

Learning outcomes:
1 Turn workpiece
Learning Activity:

1. Identify lathe types, specifications, parts and functions

The Centre Lathe

Introduction
The lathe is perhaps the most versatile of all machines in a modern workshop. It is capable of
performing a great variety of operations. They are extensively used in general engineering
workshops and tool rooms.

Figure 2.1 - The Centre Lathe

Code No. Turn Workpiece (Basic) Date: Developed Date: Revised Page #
MEE722302 1

Information Sheet 3.2.1: Lathe types, specifications, parts and functions

The Turning Operation
The lathe is a machine in which the workpiece is rotated
against the cutting tool. The cutting tool is moved
lengthwise (parallel or at an angle) to the axis of the
bed. The shape of the work depends on the operation
selected.

Figure – The Turning Operation

Work Produced on a Centre Lathe

Generally, the lathe is used to
produce cylindrical or conical jobs,
plane (flat) surfaces, able to drill and
ream holes, cut screw threads and
other operations using special
attachments. These surfaces and
threads may be external or internal to
the component.

Figure – Work Produced on a Centre Lathe

Types of Lathe
 Bench Type - These lathes are mounted on a bench or metal cabinet.
 Tool Room Type - These lathes are highly precision lathes equipped with a variety of
accessories.
 Manufacturing Type - These are bigger, heavier and more powerful than the bench type
or toolroom type.
 Turret and Capstan - The tool holder can accommodate up to 8 tools at a time.
 Special Types - The new types including CNC lathes

Code No. Turn Workpiece (Basic) Date: Developed Date: Revised Page #
MEE722302 2

Information Sheet 3.2.1: Lathe types, specifications, parts and functions

Specifications of a Lathe

A lathe is generally specified by its
 Swing (S)
 Distance Between Centres (C)

The swing is the largest diameter of a workpiece that can be swung over the lathe bed and the
distance between centres is the distance between the headstock and tailstock centres.
However, some manufacturers specify lathes by their bed length.

Figure 2.3 - Specification of a Lathe

Parts of a Lathe

Headstock
The headstock is located at the left end of the lathe bed. It contains the main spindle
mechanism for obtaining various spindle speeds. The main spindle revolves on two bearings
on each end of the headstock. The right end is made to fit a chuck or face plate.

Code No. Turn Workpiece (Basic) Date: Developed Date: Revised Page #
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Information Sheet 3.2.1: Lathe types, specifications, parts and functions

The main purpose of the headstock is:

 To transmit motive force from the motor to the main spindle by means of belts and
pulleys.

 To provide different spindle speed and feed.
 Holds workholding devices such as the chuck that holds and drives the workpiece.

Figure 2.4.1 – Headstock

Machine Bed
The lathe bed is a strong bridge like members, made from high grade cast iron and is heavily
ribbed to give it rigidity, It has four ways out of which three are inverted and one flat way. The
bed supports all the mountings of the lathe. The accuracy of the lathe depends largely on how
straight and parallel the bed ways are. It is precisely hand scraped to high dimensional and
geometrical tolerances.

On the machine bed, there are slideways, it is usually a flat and an inverted-vee slideway.
 The outer V-way and flat-way support and guide the carriage.
 The inner V-way and flat-way align the tailstock with the headstock.

Code No. Turn Workpiece (Basic) Date: Developed Date: Revised Page #
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Information Sheet 3.2.1: Lathe types, specifications, parts and functions

Figure - Machine Bed

Tailstock
It is located at the right end of the lathe, it can be adjusted along the bedway to suit the length
of work. It is made from cast iron which locates the barrel. The barrel is hollow and is bored
with a Morse-taper. This taper locates the taper shank of a dead centre and also taper shank
drills, drill chucks, etc. The bore is co-axial with the spindle that is they have a common axis
and this is a basic alignment of the lathe.

The tailstock’s primary functions are:

 To support long workpieces.
 Holds tools such as drills or reamers for drilling and reaming operation.
 For setting centre height of tool bits.

Code No. Figure – Tailstock Date: Developed Date: Revised Page #
MEE722302 5
Turn Workpiece (Basic)

Information Sheet 3.2.1: Lathe types, specifications, parts and functions

Carriage
The carriage provides various movements to the cutting tool to perform various operations on
the lathe. The three movements are:

 Longitudinal Feed
 Cross Feed
 Angular Feed

Figure – Carriage

The carriage consists of the following parts:

Apron
The apron is bolted to the front of the saddle. It
contains the mechanism for moving and
controlling the carriage. Power is transmitted to
the carriage through a gear and clutch
arrangement.

Figure

Code No. Turn Workpiece (Basic) Date: Developed Date: Revised Page #
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Information Sheet 3.2.1: Lathe types, specifications, parts and functions

Saddle
The saddle is part of the carriage that fits
across the bed slideways and moves
along the bed, between the headstock
and tailstock. It provides parallel
movement of the tool to the axis of the
bed.

Figure 2.4.4 b – Saddle

Cross Slide
The cross slide is mounted on top of the saddle and provides a cross movement for the cutting
tool (towards or away from the operator).

Compound Slide (Compound Rest)
The compound slide is mounted on top of the cross slide. As it can be swiveled to any angle, it
allows for taper turning

Toolpost
The toolpost holds the tool holder or the tool directly. There are a few types of toolposts :

 English (Clamp) type; Rigid too post
 American (Pillar) type; Standard tool post
 Turret (4-way) type
 Quick Release type

Code No. Turn Workpiece (Basic) Date: Developed Date: Revised Page #
MEE722302 7

Information Sheet 3.2.1: Lathe types, specifications, parts and functions

Figure 2.4.4 e – Toolposts

Feed Mechanism

Feed Mechanisms
The feed mechanisms consist of:

Quick Change Gear Box
The quick change gearbox provides easy change of the spindle speed and the speed for the
feedshaft and leadscrew. The reason for driving the gearbox from the spindle is that the tool
movement per revolution of the spindle must remain constant even if the spindle speed is
changed.

Code No. Turn Workpiece (Basic) Date: Developed Date: Revised Page #
MEE722302 8

Information Sheet 3.2.1: Lathe types, specifications, parts and functions
The gearbox has three functions:

 To control the speed at which the saddle is driven along the bed when power
traversing (parallel operations).

 To control the speed at which the cross slide moves across the saddle when power
cross-traversing (facing operations).

 To control the speed of the leadscrew when cutting screw threads and thus
controlling the lead of the screw being cut (thread cutting operations).

Figure 2.4.6 - Feed Mechanism
Feedshaft
The feedshaft provides automatic power feed to the carriage.
Leadscrew
The leadscrew provides thread cutting movement to the carriage for thread cutting.

Code No. Turn Workpiece (Basic) Date: Developed Date: Revised Page #
MEE722302 9

Worksheet 3.2.2: The Center Lathe
Learning outcomes:
1 Turn Workpiece
Learning Activity:
1.1 Objectives

1. Identify the types, specification, parts and function of lathe machine.

Test Your Self
Test I. Identify the functions of a carriage.

a. Apron -.
b. Saddle –

c. Cross Slide –
d. Compound Slide –
e. Tool post –

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 1

Worksheet 3.2.2: The Center Lathe
Test II. Identify the parts of a carriage

a=? b=?

c=? d=?

Test III. Multiple Choice

(1) The lathe bed is made of

(a) alloy steel
(b) Cast iron
(c) Cast steel
(d) Mild steel

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 2

Worksheet 3.2.2: The Center Lathe

(2) On which part of the lathe is the spindle?

(a) Carriage
(b) Cross slide
(c) Headstock
(d) Lathe dog

(3) The apron of the lathe is part of the

(a) Headstock
(b) Saddle
(c) Tailstock
(d) Carriage

(4) The tailstock is used to

(a) Reduce the diameter of work
(b) Measure the length of the work
(c) Support the right hand end of the work
(d) Divide the work

(5) The outer slideways of a lathe guide the

(a) Carriage
(b) Cross-slide
(c) Saddle
(d) Tailstock

(6) The inner slideways of a lathe guide the

(a) Carriage
(b) Cross-slide
(c) Saddle
(d) Tailstock

(7) The bed slideways provide an accurate surface for moving the

(a) Carriage and tailstock
(b) Headstock and tailstock
(c) Carriage and cross-slide

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Worksheet 3.2.2: The Center Lathe

(d) Cross-slide and compound slide

(8) The part of the centre lathe which supports other parts of the machine is the

(a) Carriage
(b) Headstock
(c) Lathe bed
(d) Tailstock

(9) The axis of the cross-slide is

(a) Perpendicular to the axis of the lathe
(b) 45 degrees to the axis of the lathe
(c) Parallel to the axis of the lathe
(d) Adjustable to any angle to the axis of the lathe

(10) Which part of a lathe is used in transmitting motion to the cutting tool in power
(automatic) feed ?

(a) Feedshaft
(b) Gears
(c) Half-nut
(d) Leadscrew

(11) Which part of the lathe can be swivelled to an angle for taper turning?

(a) Compound slide
(b) Cross slide
(c) Tailstock
(d) Toolpost

(12) The depth of cut is controlled by the

(a) Compound slide
(b) Cross slide
(c) Tailstock
(d) Toolpost

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 4

Worksheet 3.2.2: The Center Lathe

(13) The size of a lathe is determined by its

(a) Weight
(b) Motor capacity
(c) Length and height
(d) Swing and distance between centre

(14) Gap bed, a removable section of the bed below the chuck, is designed for the purpose
of

(a) Allowing heavier cuts
(b) Accomodating longer workpieces
(c) Providing smoother bed surfaces
(d) Accomodating larger diameter workpieces

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 5

Worksheet 3.2.2: The Center Lathe

Answer Key:

Test I. Identify the functions of a carriage

a. Apron - It houses the mechanism of the carriage.
b. Saddle - It slides on the bedways and carries the cross slide and the compound

slide.
c. Cross Slide - It provides a cross movement for the tool.
d. Compound Slide - It can be swivelled to any angle
e. Tool post - It holds the tool.

Test II. Identify the parts of a carriage

a. Apron
b. Saddle
c. Cross Slide
d. Compound Slide

Test III. Multiple Choice

(1) The lathe bed is made of

(a) alloy steel
(b) Cast iron
(c) Cast steel
(d) Mild steel

(2) On which part of the lathe is the spindle?

(b) Carriage
(b) Cross slide
(c) Headstock
(d) Lathe dog

(3) The apron of the lathe is part of the

(a)Headstock Turn Workpiece Date: Developed Date: Revised Page #
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Code No.
MEE722302

Worksheet 3.2.2: The Center Lathe

(b) Saddle
(c) Tailstock
(d) Carriage

(4) The tailstock is used to

(a) Reduce the diameter of work
(b) Measure the length of the work
(c) Support the right hand end of the work
(d) Divide the work

(5) The outer slideways of a lathe guide the

(a) Carriage
(b) Cross-slide
(c) Saddle
(d) Tailstock

(6) The inner slideways of a lathe guide the

(a) Carriage
(b) Cross-slide
(c) Saddle
(d) Tailstock

(7) The bed slideways provide an accurate surface for moving the

(a) Carriage and tailstock
(b) Headstock and tailstock
(c) Carriage and cross-slide
(d) Cross-slide and compound slide

(8) The part of the centre lathe which supports other parts of the machine is the

(a) Carriage
(b) Headstock
(c) Lathe bed
(d) Tailstock

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 7

Worksheet 3.2.2: The Center Lathe

(9) The axis of the cross-slide is

(a) Perpendicular to the axis of the lathe
(b) 45 degrees to the axis of the lathe
(c) Parallel to the axis of the lathe
(d) Adjustable to any angle to the axis of the lathe

(10) Which part of a lathe is used in transmitting motion to the cutting tool in power
(automatic feed)

(a) Feedshaft
(b) Gears
(c) Half-nut
(d) Leadscrew

(11) Which part of the lathe can be swivelled to an angle for taper turning?

(a) Compound slide
(b) Cross slide
(c) Tailstock
(d) Toolpost

(12) The depth of cut is controlled by the

(a) Compound slide
(b) Cross slide
(c) Tailstock
(d) Toolpost

(13) The size of a lathe is determined by its

(a) Weight
(b) Motor capacity
(c) Length and height
(d) Swing and distance between centre

(14) Gap bed, a removable section of the bed below the chuck, is designed for the purpose
of

(a) Allowing heavier cuts

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 8

Worksheet 3.2.2: The Center Lathe

(b) Accomodating longer workpieces
(c) Providing smoother bed surfaces
(d) Accomodating larger diameter workpieces

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 9

Information Sheet 4.1.1 : Workholding devices

Learning outcomes:
1 Turn workpiece
Learning Activity:
1.1 Identify workholding devices

Work Holding Devices

Introduction
The method for holding the workpiece depends on the type of the type of job and the
complexity of the turning process. The work holding devices must be capable of:

 Locating the work relative to the spindle axis.
 Rotating the work at the correct speed without slip.
 Preventing the work being deflected by the cutting forces. Some slender work requires

additional support.
 Holding the work sufficiently rigidly so that it will not spin out of the machine, be ejected by

cutting forces, yet not be crushed or distorted by the work holding device.

When the workholding device meets the above requirements, they are chosen by the operator
based on:
 The size of the workpiece
 The shape of the workpiece
 The accuracy required.

The following are the devices commonly used.

1. Steady Rests
A steady rest is used to support some portion of the workpiece during machining operations. It
prevents the work being bent by the cutting tool when machining. There are two types of
steadies.

a. Fixed Steady
A fixed steady is used to support a slender workpiece to prevent it from springing away
fromthe tool and bending it during machining operations. The rest can be clamped to the bed
of the lathe in any position. The fixed steady consists of a frame containing three adjustable
pads.

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
MEE722302 1

Information Sheet 4.1.1 : Workholding devices

Figure 3.2 a – Fixed Steady

b. Travelling Steady

The travelling steady is used when it is necessary to have support close to and following the
cutting tool to prevent slender work from springing. The travelling steady differs from the fixed
steady in two aspects:

 It has only two adjustable pads
 It is attached to and moves with the lathe saddle

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices

Figure 3.2b – Travelling Steady

2. Face Plate
Large, flat, irregular shaped workpieces and castings, jigs and fixtures that cannot be gripped
in a chuck or mounted between centers may be clamped to a face plate for machining
operations.

A face plate is similar to a lathe drive plate except that it is as large as the lathe would allow. It
is fitted to the spindle nose and contains a number of T-slots and/or elongated holes to
accommodate bolts and clamps. When the face plate is mounted on the lathe spindle, the face
is at right angles to the centerline of the lathe.

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
MEE722302 3

Information Sheet 4.1.1 : Workholding devices

Figure 3.3 – Face Plate

Advantages of Using the Face Plate

 A wide range of regular and irregular components can be held.
 Work can be set to a datum surface. If he datum surface is parallel to the workpiece

axis, it is set to an angle plate mounted on the face plate. If the datum surface is
perpendicular to the workpiece axis, the workpiece is set directly on to the face
plate.
 Work on the end face of the job is possible.
 The work can be bored.
 The work can be set to run concentrically or eccentrically at will.
 There are no moving parts to lose their accuracy with wear.
 The work can be rigidly clamped to resist heavy cuts.

Limitations of Using the Face Plate

 The face plate is slow and tedious to set up. Not only must the workpiece be clocked
up to run true, clamps must also be set up on the face plate to retain the component.

 Considerable skill is required to clamp the component so that it is rigid enough to
resist both the cutting forces, and those forces that will try to dislodge the work as it
spins rapidly round.

 Considerable skill is required to avoid distorting the workpiece by the clamps.
 Irregular jobs have to be carefully balanced to prevent vibration and the job rolling

back on the operator.
 The clamps can limit the work that can be performed on the end face.

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
MEE722302 4

Information Sheet 4.1.1 : Workholding devices

3. Collet Chuck

Collet chucks or collets as they are normally called provides a means of clamping rods of
material or previously part-machined components. The rods are usually small in diameter and
large quantities are required. As the collet is self-centering, it has a high degree of
concentricity. There are three commonly used collets.

a. Spilt Collet Chuck

The collet is tapered to fit the conical hole of the taper sleeve and is slotted to permit the collet
to contract and expand when drawn into or released from the taper sleeve.

Figure 3.4.1 – Split Collet Chuck

Figure 3.4.1 - Split Collet Chuck Assembly

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices

b. Spring Collet Chuck

Spring collet chucks are mounted on the lathe spindle in the same manner as a chuck or drive
plate. Since they are not held in place by a draw bar, they can accommodate larger diameter
bars.

c. Spindle Nose Collet Chuck

The spindle nose collet chuck has a rubber flex collet consisting of a series of metal inserts
moulded into rubber. These collets are very flexible, each collet having a range of
approximately 3mm which allows a much wider range of workpieces to be accommodated
with fewer collets.

Advantages of Using Collet Chucks

 Very high accuracy of concentricity.
 Accuracy maintained over long periods of use.
 Simple, compact and reliable.
 Very quickly loaded.
 Considerable gripping power.
 Unlikely to mark or damage work.
 Work can be removed and replaced without loss of accuracy.
 Work can be turned externally, internally and end faced,
 No overhang from spindle nose reduces chatter and geometrical inaccuracy. Very

useful where work has to be “parted off”.

Limitations of Using Collet Chucks

 Only accurately turned, ground or drawn rod can be held in a collet.
 Separate collets have to be used for each size of rod. Range of adjustments very

small.
 Although simple, initial costs is high due to the large number of collets that have to

be bought.
 Range of sizes that can be held limited by bore size.
 Work can only be held on external surfaces.
 Only collets with circular or hexagonal jaws are available from stock. Other sections

have to be made to special order (costly).

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices

 Special adaptor sleeve required to suit bore of spindle.

4. Jaw Universal Chuck

The 3-Jaw chuck is the most widely used because of its self-centring property. The jaws move
in and out simultaneously together. Thus is why it is called a Self-Centring chuck or Universal
chuck. A chuck key is used to rotate a scroll plate that moves the three jaws simultaneously at
the same distance.

Generally, two sets of jaws are provided. One set is used for holding work externally and the
other for holding work internally. The 3-jaw chuck is used for holding round, triangular or
hexagonal work. It is not suitable for holding work with “scales” as it will damage the chuck.

Figure 3.5 – 3-Jaw Universal Chuck
Advantages of Using a 3-Jaw Universal Chuck

 The work can be set up easily as it is self-centring.
 A wide range or cylindrical and hexagonal work can be held.
 Internal and external jaws are available.
 Work can be readily performed on the end face of the job.
 The work can be drilled and bored.

Limitations of Using the 3-Jaw Universal Chuck

 Accuracy decreases as chuck becomes worn.

 Accuracy of concentricity is limited when the work is reversed in the chuck.

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices

 “Run-out” cannot be corrected.
 Only round, triangular and hexagonal components can be held.
 It is not suitable for resetting precise work.

Different Chucking using 3-jaw

5. 4-Jaw Independent Chuck

Where a high degree of accuracy is required, the work is generally mounted in a 4-jaw
independent chuck. A 4-Jaw independent chuck is much more heavily constructed than the 3-
Jaw chuck and has much more holding power. Each jaw of the chuck can be adjusted
independently and work can be trued to within 0.025mm. The jaws are reversible and permit a
wide range of work to be gripped either externally or internally.

Round, square, octagonal, hexagonal and irregularly shaped workpieces can be held and

adjusted to run concentrically or off-centre as required. The face of the chuck has a number of

evenly spaced concentric grooves which permit quick and approximate positioning of the

chuck jaws.

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices

Figure 3.6.3 - 4-Jaw Independent Chuck

Advantages of Using the 4-Jaw Independent Chuck

 A wide range of regular and irregular shapes can be held.
 Work can be set to run concentrically or eccentrically at will.
 Heavy cuts can be taken, as the gripping power is better.
 Jaws are reversible for internal and external work.
 Work can be readily performed at the end face of the job.
 The work can be drilled and bored.
 There is no loss of accuracy as the chuck becomes worn.

Limitations of the 4-Jaw Independent Chuck

 Chuck is heavy and bulky to handle on the lathe.
 Chuck is slow to set up. A dial test indicator has to be used for accurate setting.

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices

 The gripping power is so great that the fine work can be easily damaged during
setting.

Setting-Up Round Bars in a 4-Jaw Chuck

When setting-up round bars in the 4-jaw chuck, you can do it by the approximate
method or the accurate method.
 Approximate Method

o Using the concentric rings
o With a surface gauge
o With a tool holder
o
 Accurate Method
o Using dial test indicator

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices

Figure 3.6.3 – Setting Up Work in a 4-Jaw Chuck

6. Turning Between Centres

If a workpiece is long, it is usually held between centres. The workpiece is held between two
centres at the headstock and tailstock. The workpiece is driven by a lathe dog and drive plate.

Figure 3.7– Work Held Between Centres

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices
The centres, themselves, have Morse-taper
shanks and are located in taper sockets in the
spindle and tailstock barrel. A lathe dog or carrier
and a drive plate drive the workpiece. The
following are the accessories required for turning
between centres.

Figure 3.7 – Driving the Workpiece Between Centres
7. Drive Plate

The drive plate is connected to the headstock spindle and provides the rotating motion.
It drives the lathe dog which in turn turns the workpiece. The two drive plates used are:
 Drive slot
 Drive pin

Figure 3.7.1 – Drive Plate

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices
8. Lathe Dog or Carrier
The lathe dog or carrier are used to hold and drive the workpiece. There are two types
of lather carriers:
 Bent tail carrier
 Straight tail carrier
The bent tail carrier is used with the drive slot drive plate and the straight tail carrier is
used with the drive pin drive plate.

Figure 3.7.2 – Lathe Carrier ( Lathe Dog )

Figure 3.7.2 Method of Driving Work

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Information Sheet 4.1.1 : Workholding devices

9. Lathe Centres

The centres are held in the tapered bore of the headstock and tailstock spindles. It supports
the right end of the workpiece to be turned between centres. There are a few types of
centres:

a. Plain Centre
The plain centre is used in the headstock (live centre) or in the tailstock (dead centre).

Figure 3.7.3a - Plain Centres

b. Revolving Centre
The revolving centre runs on ball bearings. It rotates with the work and is recommended
for work turning at high speeds.

F
igure 3.7.3b – Revolving Centr

c. Half Centre
The half centre is used in the tailstock to provide clearance for the tool to do facing. It also
provides clearance for turning small diameter work.

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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Information Sheet 4.1.1 : Workholding devices
Figure 3.7.3c – Half Centre

Figure 3.7 – Turning Between Centres

Advantages of Work Holding Between Centres
 Work can be easily reversed without loss of concentricity.
 Work can be taken from the machine for inspection and easily reset without loss of
concentricity.
 Work can be transferred between machines (eg. Lathe and cylindrical grinder)
without loss of concentricity.
 Long work (full length of bed) can be accommodated.

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Information Sheet 4.1.1 : Workholding devices

Limitations of Work Holding Between Centres

 Centre holes have to be drilled before work can be set up.
 Only limited work can be performed on the end of the bar.
 Boring operations cannot be performed.
 There is a lack of rigidity.
 Cutting speeds are limited unless a revolving centre is used. This reduces accuracy

and accessibility.
 Skill in setting is required to obtain the correct fit between centres and work.

Precautions when Turning Work Between Centres

 Make sure that the centre holes are properly drilled
 Clean the workpiece and equipment before setup
 Apply grease in the centre hole at the dead centre end to reduce friction
 Choose appropriate size lathe dog for the workpiece
 Fit the workpiece between centres; it should not be too tight nor too loose
 Do not part-off workpiece held between centres

Aligning the Lathe Centres

The lathe centres must be aligned before
any work turned between centres is done.
If they are not aligned, the workpiece produced
would not be accurate and a tapered workpiece
will be produced.

Figure 3.8 – Effects of Non-Aligned Centres

There are four methods:

 Less Accurate Methods:
o Using tailstock graduations.
o Visual alignment.

 More Accurate Methods:
o Test bar and Dial Test Indicator
o Trial Cut Method

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Information Sheet 4.1.1 : Workholding devices

Using Tailstock Graduations
At the back of the tailstock there are
graduations, align the two “0” lines; one
on the base and one on the tailstock
body. Turning the adjusting screw
moves the tailstock. This method is not
very reliable once the lathe gets older.

Figure 3.8.1 – Using Tailstock Graduations

Visual Alignment

Move the tailstock centre to meet the
headstock centre. Adjust the tailstock to
ensure that the two points meet.
As this depends only on visual aids,
accuracy is
not very good.

Figure 3.8.2 – Visual Alignment

Using a Test Bar and Dial Indicator

A test bar is mounted between centres. A dial indicator is used to take readings on the two
ends of a test bar. Adjust the tailstock until the readings taken are the same. The centres are
aligned when the readings at the two ends of the test bar are the same.

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Information Sheet 4.1.1 : Workholding devices

Figure 3.8.3 – Using a Test Bar and Dial Indicator
Trial Cut Method
A workpiece is held between centres. Take trial cuts at the two ends of the workpiece.
Measure the two ends with a micrometer. If the readings are different, adjust the tailstock.
Keep on taking trial cuts until the readings are the same. The centres are aligned when the
diameters cut of the same diameter.

Figure 3.8.4 – Trial Cut Method

Code No. Turn workpiece (basic) Date: Developed Date: Revised Page #
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