Turning Workpiece (Basic)

Information Sheet 9.2.7: Taper Turning

When the offset is great, the plain centres used for supporting the work for taper turning will
not provide sufficient support. It will also damage the centre hole. Ball centres should be used
instead.

Figure 11.21 – Centre Support for Offsetting Tailstock Method

Checking the Accuracy of Tapers

Using taper gauges can check the size and fit of the tapers.
 Taper ring gauges are used for checking external tapers.
 Taper plug gauges are used for checking internal tapers.

Figure 18.6 – Gauges for Checking Tapers

Checking External Tapers
The accuracy of an external taper depends on:

 The included angle.
 The diameter.
 The length.

A correct external taper has:

 A good fit with the taper ring gauge.
 Its big diameter must lie between the high and low limit of the taper ring gauge.

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 9.2.7: Taper Turning

Figure 18.6.1 –
Checking External Tapers
External Taper Fault

Figure 18.6.2 – External Taper Faults

Checking Internal Tapers
The accuracy of an internal taper depends on:

 The included angle.

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 9.2.7: Taper Turning
 The diameter.
 The length.

A correct internal taper has:
 A good fit with the taper plug gauge.
 Its big diameter must lie between the high and low limit of the taper plug gauge.

Figure 18.6.3 – Checking Internal Tapers
Internal Taper Faults

Figure 18.6.4 – Internal Taper Faults

Code No. Turn Workpiece Date: Developed Date: Revised Page #
MEE722302 15

Worksheet : 9.8.2. – Taper turning

Learning outcomes:
1 Turn Workpiece
Learning Activity:
1.2 Objectives

1. Discuss the common ways of specifying a standard and non-standad taper viz: :
• Included angle
• Ratio
• Morse taper
• International taper

2. Determine the half-included angle of the taper.
3. Describe the correct set up of work and tool for taper turning.
4. State the common problems encountered,their faults and remedies
5. Explain how to check external tapers for size and accuracy using the appropriate

gauges.

Test Your Self

1. In taper turning, swivelling the compound slide method is used to cut
A. Long tapers.
B. Short tapers.
C. Long workpieces.
D. Steps and shoulders.

2. To turn a taper by swivelling the compound slide, the top slide should be set to
A. The included angle.
B. Half the included angle.
C. Two times the included angle.
D. Three times the included angle.

3. Refer to Fig 1. At what angle should the compound slide be swivelled to turn the taper
shown?

A. 3°.
B. 6°.
C. 12°.
D. 18°.

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Worksheet : 9.8.2. – Taper turning

4. A non-standard taper on a workpiece is expressed in
A. Ratio or Angle.
B. Morse taper number.
C. Brown and Sharpe taper.
D. International taper

5. When turning a taper by the compound slide method, the length of the taper is controlled by
the length of the

A. Work.
B. Bed ways.
C. Top slide way.
D. Cross slide way.

6. A taper of 40 (included angle) is to be turned by swiveling the compound slide, the top slide
should be set to

A. 10.
B. 20.
C. 40.
D. 80.

7. To turn a taper of 60 degrees included angle, the compound slide should be set to
A. 30 degrees.
B. 60 degrees.
C. 90 degrees.
D. 120 degrees.

8. In taper turning, if the compound slide is set at 20, the included angle of the taper would be
A. 10.
B. 20.
C. 30.
D. 40.

9. A quick method of turning a taper of 10mm x 30 included angle on a lathe is by
A. Free hand method.
B. Offsetting the tailstock.
C. Swiveling the compound slide.
D. Using a taper turning attachment.

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Worksheet : 9.8.2. – Taper turning

10. Swiveling compound slide method of taper turning is suitable for turning
A. Very long tapers.
B. Long and fast tapers.
C. Slow and accurate tapers.
D. Short tapers of any angles.

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Worksheet : 9.8.2. – Taper turning

Answer Key:

1. (B) Short tapers
2. (B) half the included angle.
3. (B) 6°.
4. (A) Ratio or Angle.
5. (C) top slide way.
6. (B) 20.
7. (A) 30 degrees.
8. (A) 10.
9. (C) swivelling the compound slide
10. (D) short tapers of any angles.

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 9.2.8: Screw Thread
Learning outcomes:
1 Turn workpiece
Learning Activity:

1. Define threading operation.
2. Explain the procedures of threading operation

ISO Metric Thread

Screw Threads
A screw thread is a helical groove formed on a cylindrical work. The thread may be on an
external surface or an internal surface. A bolt has an external thread. A nut has in internal
thread. The spiral ridge of the thread is of uniform shape or profile throughout its length.

The thread may be produced using hand tools, such as taps and dies, or by machine tools.
One of the most frequently used machine tools for producing threads is the centre lathe. The
thread is produced by cutting a spiral groove in the surface of a rotating workpiece.

Figure 19.1 – External and Internal Threads

Uses of Screw Threads

Screw threads are used for:
 Holding parts together, such as bolts and nuts.

Figure 19.2a – Bolts and Nuts

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 9.2.8: Screw Thread
 Transmitting power, such as screw jacks

Figure 19.2b – Screw Jacks
 Measuring device mechanisms, e.g. the threaded spindle of a micrometer

Figure 19.2c – Threaded Spindle of a Micrometer
Parts of a Screw Thread

Figure 19.3a – Parts of a Screw Thread

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 9.2.8: Screw Thread
The parts of a screw thread are identified by the following terms:

Term Description
Major Diameter The largest diameter of a straight external or internal thread.

Minor Diameter The smallest diameter of a straight external or internal thread.
Pitch Diameter
Pitch The distance between diametrically opposite points on a straight
Flank thread. It is equal to the major diameter minus one depth.
Root The distance from one point on one thread to a corresponding
Crest point on the next thread, measured parallel to the axis.
Thread Angle
Depth The surface connecting crest and roof.
Lead
The bottom surface joining the flanks of adjacent threads. The
root diameter is same as the minor diameter.

The top surface of the thread bounded by the flanks.

The included angle between the flanks of adjacent turns of the
thread.
The perpendicular distance between the root and crest of the
thread.
The distance a threaded surface moves parallel to the axis of the
thread during one complete revolution.

Figure 19.3c – Screw Thread Terminology

Hand of Thread
Screw threads can be cut to right hand or left hand thread depending on its function. It refers to
the direction in which the thread is turned to advance. A right hand thread is turned clockwise
to advance. A left hand thread is turned anti-clockwise to advance.

Figure 19.4 – Hand of Thread

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Information Sheet 9.2.8: Screw Thread
Features of ISO Metric Thread
Designation of ISO Metric Thread

The ISO metric vee thread is designated as follows:
M 20 x 1.5

Metric Pitch
Thread
Major
Diameter

Standard Pitches
All ISO metric threads have standard pitches. Coarse threads have larger pitches. The pitches
of the ISO Vee thread differ in coarse or fine depending on their uses.

Figure 19.5.2a – Vee Threads with Coarse and Fine Pitch

The metric coarse threads have coarser pitches for the same diameter threads. They are used
for general purposes.

Figure 19.5.2b – Coarse Pitch
The metric fine threads do not become loose easily when there is vibration.

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Information Sheet 9.2.8: Screw Thread

Figure 19.5.2c – Fine Pitch
Types of Thread Forms
Screw threads can be cut to different thread forms to suit the application they are used in. The
following are some of the forms available.
ISO Metric Vee Thread
They are the most commonly used thread form and are used on screws, bolts, studs and
micrometer spindles.

Figure 19.5.1 – Use of Metric Vee Thread

Trapezoidal Metric Thread
Trapezoidal Metric thread has a thread angle of 30.

Figure 19.5.2 – Trapezoidal Metric Thread

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Information Sheet 9.2.8: Screw Thread

For external threads : Depth ( D ) = ( 0.5 x Pitch ) + Clearance
For internal threads : Depth ( D ) = ( 0.5 x Pitch ) - Clearance

Generally, the roots are rounded to the radius ( r ), 0.25mm.
The Trapezoidal metric thread is designated as follows:

Tr 8 x 1.25

Trapezoidal Pitch
Thread
Major
Diameter

Trapezoidal threads are used mainly for power transmission, eg. the leadscrew of the lathe.

Square Thread
Square threads are used mainly for heavy duty power transmission, eg. machine vice screw.

Figure 19.6.3 – Square Thread

For Square threads:

Depth = 0.5 x Pitch

Width ( W ) = 0.5 x Pitch ( External Thread )

Width ( W1) = 0.5 x Pitch + 0.05 ( Groove of internal thread )

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Information Sheet 9.2.8: Screw Thread

Vee-Threads Cutting on Centre Lathe
Threads are cut on a lathe by rotating a cylindrical workpiece at a constant speed and
machining the surface of the workpiece with a cutting tool. The cutting tool is moved at a
constant speed in a direction parallel to the axis of the workpiece.

The cutting tool moves with the lathe carriage by engagement of a half nut with the lathe lead
screw. The shape of the cutting tool determines the shape of the groove cut in the workpiece,
and therefore, the profile of the thread.

Figure 20.1 – Using the Half Nut for Thread Cutting

Setting Up the Lathe Quick Change Gearbox for Thread Cutting

During a thread cutting operation on a lathe the cutting tool is mounted on the lathe carriage.
The carriage is moved along the lathe bed by the action of the half nut following the thread of
the rotating lead screw.
The leadscrew is rotated by an intermediate gearbox driven by the lathe spindle. The gearbox
provides the necessary variations in speed and direction of rotation of the leadscrew to enable
threads of various pitches to be cut.

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Information Sheet 9.2.8: Screw Thread
On new lathes, quick change gearboxes are fitted to help in setting up the desired leadscrew
speed. Gear changing is effected by movement of two levers and a sliding gear. The relative
positions of the levers and sliding gear for a given number of threads per unit length is
indicated on a chart fitted to the machine.

Figure 20.2 – Quick Change Gearbox
Example :

To cut a thread with a 3mm pitch, the steps are :
 Move lever “ X ” to position “ B ”.
 Move lever “ Y ” to the hole below column in which “ 3.0 ” can be found.

Figure 20.2.1 – Setting the Quick Change Gearbox

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Information Sheet 9.2.8: Screw Thread

Thread Chasing Dial
To produce a smooth accurately profiled thread the cut is made with several passes of the
cutting tool. The depth of the thread is increased with each successive cut.

At the end of each pass, it is necessary to withdraw the tool from the cut and accurately
position it to ensure that the path of the first cut is followed by the successive cuts.

In practice, this means that the carriage half nut is disengaged from the leadscrew at the end
of each pass. The carriage is then returned to the starting position and the leadscrew
reengaged with the half nut. Even though the tool may be correctly positioned, if the leadscrew
is engaged with the half nut at the wrong instant, the tool will not follow the original cut and an
unwanted second groove will then be cut in the workpiece.

To eliminate this possibility, a thread chasing dial mechanism is used. The mechanism which
is fixed to the carriage, consists of a rotating graduated dial. The dial is rotated by a worm gear
which meshes with the leadscrew.

By noting the movement of the graduated dial with respect to an index line, it is possible to
determine the correct instant for engaging the leadscrew with the half nut.

Figure 20.2.2 – Thread Chasing Dial

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Information Sheet 9.2.8: Screw Thread
Methods of Feeding the Threading Tool
There are two commonly methods used for feeding the threading tool :

a. Plunge Cutting Method
In the plunge cutting method, the depth of cut is reduced gradually, starting from 0.5mm per
cut to as low as 0.2mm per cut. To provide clearance and to prevent the tool from digging into
the work, use the compound slide to move the load to either side at about 0.1mm per cut.

Figure 20.3a – Plunge
Cutting Method

b. Side Cutting ( Angular Approach ) Method
c.
In the side cutting method, the tool is fed into the work at an angle of about 29 to the
cross slide axis.

Figure 20.3b – Side Cutting Method

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 9.2.8: Screw Thread
Preparation for Cutting the Threads
Before cutting the thread, the work is turned to the major diameter of the thread. It is good
practice to cut a groove at the shoulder. This groove or undercut will allow the threading tool to
run out. It also allows parts to fit flatly onto each other.
Chamfer the end of the work before the actual thread cutting operation.

Figure 20.4 – Preparing the Work for Thread Cutting
Vee Threading Tool
The threading tool bit is ground to the 60 thread angle. To check the angle of 60 thread
cutting tool a centre gauge may be used. Alternatively, a flat gauge may be used.

Figure 20.4.1 – Thread Cutting Tool

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 9.2.8: Screw Thread
Centre Gauge
The centre gauge is used to set the threading tool square to the work.

Figure 20.4.2 – Centre Gauges

Figure 20.4.2 – Setting Threading Tool Square to the Work

The workpiece may be held in a chuck, in a chuck and the tailstock centre or between
centres.

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Information Sheet 9.2.8: Screw Thread
Procedures for Screw –cutting an External Vee-thread
Cutting Right-hand & Left-hand Threads
For right-hand threads, the tool cuts from the tailstock towards the headstock.

Figure 20.5.1a – Right-Hand Thread
For left-hand threads, the tool cuts from the headstock towards the tailstock.

Figure 20.5.1b – Left-Hand Thread

Required Steps
The thread cutting operation can be divided into three steps :

a. Taking Trial Cut
 Chamfer the end of the workpiece with the leading edge of the cutting tool to a

depth just greater than the minor diameter of the thread to be cut.
 Set the tip of the cutting tool to the workpiece surface.
 Move to the right of the workpiece and feed the tool in about 0.1mm
 Engage the half nut and take a trial cut along the length of the workpiece to be

threaded.

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 9.2.8: Screw Thread

 At the end of the trial cut, immediately wind the cutting tool clear of the workpiece
by operating the cross slide handle.

Figure 20.5.2a – Taking a Trial Cut
 Check the pitch of the thread cut with a screw pitch gauge or use a steel rule.

Figure 20.5.2a – Check the Pitch

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Information Sheet 9.2.8: Screw Thread
b. Taking the Roughing Cut
 Engage the tool to move in the reverse direction.
 Return the tool to the starting point.
 Set the new depth of cut.
 The first 2 cuts should be about 0.4mm deep and succeeding cuts about 0.25mm
 Cut the thread again by moving the tool in the forward direction by engaging the
half nut.

Figure 20.5.2b – Taking the Roughing Cut

c. Taking the Finishing Cut
 Use a feed of about 0.03mm for the depth of cut for the finishing cut.
 Check the finish thread with a gauge.

Figure 20.5.2c – Taking the Finishing Cut

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Information Sheet 9.2.8: Screw Thread

Checking the Threads
A thread must be cut with accuracy to ensure a proper fit with a mating thread.
There are accurate gauges used for checking the thread cut:
 Thread calliper gauge
 Screw ring gauge
 Screw plug gauge
Besides these gauges, a more quick way to check the thread cut is by either using a screw
pitch gauge to check the pitch and by using a nut to check the fit.

Figure 20.6 – Checking the Threads

Figure 20.6a – Different Tools used to check the Thread

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Information Sheet 1.1.1 :

Learning outcomes:
1 Turn workpiece
Learning Activity:
1.1
20.0 Vee-Threads Cutting on Centre Lathe

20.1 Introduction

Threads are cut on a lathe by rotating a cylindrical workpiece at a constant speed and
machining the surface of the workpiece with a cutting tool. The cutting tool is moved at a
constant speed in a direction parallel to the axis of the workpiece.

The cutting tool moves with the lathe carriage by engagement of a half nut with the lathe lead
screw. The shape of the cutting tool determines the shape of the groove cut in the workpiece,
and therefore, the profile of the thread.

Figure 20.1 – Using the Half Nut for
Thread Cutting

Code No. Servicing Starting System Date: Developed Date: Revised Page #
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Information Sheet 1.1.1 :

20.2 Setting Up the Lathe Quick Change Gearbox for Thread Cutting

During a thread cutting operation on a lathe the cutting tool is mounted on the lathe
carriage. The carriage is moved along the lathe bed by the action of the half nut
following the thread of the rotating lead screw.

The leadscrew is rotated by an intermediate gearbox driven by the lathe spindle. The
gearbox provides the necessary variations in speed and direction of rotation of the
leadscrew to enable threads of various pitches to be cut.

Code No. Servicing Starting System Date: Developed Date: Revised Page #
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Information Sheet 1.1.1 :
On new lathes, quick change gearboxes are fitted to help in setting up the desired
leadscrew speed. Gear changing is effected by movement of two levers and a sliding
gear. The relative positions of the levers and sliding gear for a given number of threads
per unit length is indicated on a chart fitted to the machine.

Figure 20.2 – Quick Change Gearbox

20.2.1 Example :
To cut a thread with a 3mm pitch, the steps are :
 Move lever “ X ” to position “ B ”.
 Move lever “ Y ” to the hole below column in which “ 3.0 ” can be found.

Code No. Servicing Starting System Date: Developed Date: Revised Page #
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Mar 01, 2006 3

Information Sheet 1.1.1 :
Figure 20.2.1 – Setting the Quick Change Gearbox

Code No. Servicing Starting System Date: Developed Date: Revised Page #
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Information Sheet 1.1.1 :

20.2.2 Thread Chasing Dial

To produce a smooth accurately profiled thread the cut is made with several passes of
the cutting tool. The depth of the thread is increased with each successive cut.

At the end of each pass, it is necessary to withdraw the tool from the cut and
accurately position it to ensure that the path of the first cut is followed by the successive
cuts.

In practice, this means that the carriage half nut is disengaged from the leadscrew at
the end of each pass. The carriage is then returned to the starting position and the
leadscrew reengaged with the half nut. Even though the tool may be correctly
positioned, if the leadscrew is engaged with the half nut at the wrong instant, the tool
will not follow the original cut and an unwanted second groove will then be cut in the
workpiece.

To eliminate this possibility, a thread chasing dial mechanism is used. The mechanism
which is fixed to the carriage, consists of a rotating graduated dial. The dial is rotated by
a worm gear which meshes with the leadscrew.

By noting the movement of the graduated dial with respect to an index line, it is possible
to determine the correct instant for engaging the leadscrew with the half nut.

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ALT723307 Aug 15, 2003
Mar 01, 2006 5

Information Sheet 1.1.1 :
Figure 20.2.2 – Thread Chasing Dial

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Information Sheet 1.1.1 :
20.3 Methods of Feeding the Threading Tool
There are two commonly methods used for feeding the threading tool :
a. Plunge Cutting Method
In the plunge cutting method, the depth of cut is reduced gradually, starting from 0.5mm
per cut to as low as 0.2mm per cut. To provide clearance and to prevent the tool from
digging into the work, use the compound slide to move the load to either side at about
0.1mm per cut.

Figure 20.3a – Plunge
Cutting Method

b. Side Cutting ( Angular Approach ) Method
In the side cutting method, the tool is fed into the work at an angle of about 29 to the
cross slide axis.

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Information Sheet 1.1.1 :
Figure 20.3b – Side Cutting Method

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Information Sheet 1.1.1 :
20.4 Preparation for Cutting the Threads
Before cutting the thread, the work is turned to the major diameter of the thread. It is
good practice to cut a groove at the shoulder. This groove or undercut will allow the
threading tool to run out. It also allows parts to fit flatly onto each other.
Chamfer the end of the work before the actual thread cutting operation.

Figure 20.4 – Preparing the Work for Thread Cutting
20.4.1 Vee Threading Tool

The threading tool bit is ground to the 60 thread angle. To check the angle of 60
thread cutting tool a centre gauge may be used. Alternatively, a flat gauge may be used.

Code No. Servicing Starting System Date: Developed Date: Revised Page #
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Information Sheet 1.1.1 :
Figure 20.4.1 – Thread Cutting Tool

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Information Sheet 1.1.1 :
20.4.2 Centre Gauge
The centre gauge is used to set the threading tool square to the work.

Figure 20.4.2 – Centre Gauges

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Information Sheet 1.1.1 :
Figure 20.4.2 – Setting Threading Tool Square to the Work

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Mar 01, 2006 12

Information Sheet 1.1.1 :
The workpiece may be held in a chuck, in a chuck and the tailstock centre or between
centres.

20.5 Procedures for Screw –cutting an External Vee-thread
20.5.1 Cutting Right-hand & Left-hand Threads
For right-hand threads, the tool cuts from the tailstock towards the headstock.

Figure 20.5.1a – Right-Hand Thread
For left-hand threads, the tool cuts from the headstock towards the tailstock.

Figure 20.5.1b – Left-Hand Thread

20.5.2 Required Steps
The thread cutting operation can be divided into three steps :

a. Taking Trial Cut

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Information Sheet 1.1.1 :

 Chamfer the end of the workpiece with the leading edge of the cutting tool to a
depth just greater than the minor diameter of the thread to be cut.

 Set the tip of the cutting tool to the workpiece surface.
 Move to the right of the workpiece and feed the tool in about 0.1mm
 Engage the half nut and take a trial cut along the length of the workpiece to be

threaded.

Code No. Servicing Starting System Date: Developed Date: Revised Page #
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Mar 01, 2006 14

Information Sheet 1.1.1 :

 At the end of the trial cut, immediately wind the cutting tool clear of the workpiece
by operating the cross slide handle.

Figure 20.5.2a – Taking a Trial Cut
 Check the pitch of the thread cut with a screw pitch gauge or use a steel rule.

Code No. Servicing Starting System Date: Developed Date: Revised Page #
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Information Sheet 1.1.1 :
Figure 20.5.2a – Check the Pitch

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Information Sheet 1.1.1 :
b. Taking the Roughing Cut
 Engage the tool to move in the reverse direction.
 Return the tool to the starting point.
 Set the new depth of cut.
 The first 2 cuts should be about 0.4mm deep and succeeding cuts about 0.25mm
 Cut the thread again by moving the tool in the forward direction by engaging the
half nut.

Figure 20.5.2b – Taking the Roughing Cut

c. Taking the Finishing Cut
 Use a feed of about 0.03mm for the depth of cut for the finishing cut.
 Check the finish thread with a gauge.

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Information Sheet 1.1.1 :
Figure 20.5.2c – Taking the Finishing Cut

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Information Sheet 1.1.1 :
20.6 Checking the Threads

A thread must be cut with accuracy to ensure a proper fit with a mating thread.

There are accurate gauges used for checking the thread cut:

 Thread calliper gauge
 Screw ring gauge
 Screw plug gauge

Besides these gauges, a more quick way to check the thread cut is by either using a screw

pitch gauge to check the pitch and by using a nut to

check

the fit.

Figure 20.6 – Checking the Threads

Code No. Servicing Starting System Date: Developed Date: Revised Page #
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Information Sheet 1.1.1 :
Figure 20.6a – Different Tools used to check the Thread

Code No. Servicing Starting System Date: Developed Date: Revised Page #
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Worksheet 1.1.1: Screw Thread

Learning outcomes:
1 Turn Workpiece
Learning Activity:
1.1. Objectives

1. Explain the techniques in screw cutting external vee thread on the centre lathe
2. Explain the ways to prevent common faults

Test Yourself

1) The depth of an iso internal vee thread is calculated as

A. 0.50 time pitch
B. 0.54 time pitch
C. 0.61 time pitch
D. 0.65 time pitch

2) The depth of an external iso metric vee thread specified as M16 X 2 is

A. 1.08mm
B. 1.22mm
C. 2.0mm
D. 14.0mm

3) Screw thread cutting is carried out by engaging the

A. apron
B. carriage
C. feed shaft
D. lead screw

4) The function of the lead screw on a centre lathe is
to provide

A. automatic feed to the carriage
B. automatic feed for screw cutting
C. automatic feed for the cross-slide
D. automatic feed to the compound slide

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Worksheet 1.1.1: Screw Thread
5) A screw pitch gauge is used to

A. set the tool
B. check the thread depth
C. check the pitch
D. check the surface finish of the thread flank

6) A metric thread of m33 time 3.0 means that the major diameter is

A. 30mm and the pitch is 3.0mm
B. 33mm and the pitch is 3.0mm
C. 30mm and the undercut is 3.0mm
D. 33mm and the undercut is 3.0mm

7) If a metric vee thread is given as m20 time 2.5,its major diameter is

A. 17.5mm
B. 20.0mm
C. 22.5mm
D. 50.0mm

8) A metric thread is specified as M10 X 1.25. What does 1.25 mean?

A. lead of the thread
B. pitch of the thread
C. depth of the thread
D. major diameter of the thread

9) A metric thread is specified as M10 X 1.25. What does 1.25 mean?

A. lead of the thread
B. pitch of the thread
C. depth of the thread
D. major diameter of the thread

10) An ISO thread specification is given as M20 X 2, 3-start. This mean that it has

A. 2mm pitch and 3mm lead

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Worksheet 1.1.1: Screw Thread

B. 2mm pitch and 6mm lead
C. 3mm pitch and 2 mm lead
D. 3mm pitch and 6 mm lead

11) The size of an ISO metric thread is given as M20 X 2.5. The number 20 refer to the

A. core diameter
B. major diameter
C. minor diameter
D. pitch diameter

12) When cutting a left-hand external thread, the tool must travel

A. across the bed way
B. from left to right
C. from right to left
D. towards the headstock

13) In cutting a single-start thread on a centre lathe, the quick-change gear box is set to the

A. angle of the thread
B. depth of the thread
C. pitch of the thread
D. width of the thread

14) In a screw thread, the lead is equal to

A. no. of starts time pitch
B. no. of start/pitch
C. pitch/no of starts
D. pitch-no, of start

15) A tool which is used to set a vee-threading tool square with a workpiece is the

A. centre gauge
B. gauge block
C. pitch gauge
D. square head

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Worksheet 1.1.1: Screw Thread

16) A screw thread micrometer is used for measuring the

A. pitch of the thread
B. minor diameter of the thread
C. major diameter of the thread
D. effective diameter of the thread

17) A threading tool is fed from the headstock to the tailstock when cutting a

A. square thread
B. left-hand thread
C. right-hand thread
D. trapezoidal thread

18) In order to obtain a good surface finish on the thread, the last few cuts should be

A. deeper cuts
B. lighter cuts
C. no feed of tool
D. carried out with the split nut disengaged

19) The lathe carriage is engaged to the leadscrew for thread cutting by means of the

A. apron
B. half nut
C. feed shaft
D. thread chasing dial

Code No. Turn Workpiece Date: Developed Date: Revised Page #
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Worksheet 1.1.1: Screw Thread

Answer Key:

1. B
2. B
3. D
4. B
5. C
6. B
7. B
8. B
9. B
10. B
11. B
12. B
13. C
14. A
15. A
16. D
17. B
18. B
19. B

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