Mechanical Workshop Module 7: Tapping and Threading PREPARED BY Academic Services January 2012 © Applied Technology High Schools, 2012
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Mechanical Workshop
Module 7: Tapping and Threading
PREPARED BY
Academic Services
January 2012
© Applied Technology High Schools, 2012
ATM-1022 – Mechanical Workshop
2 Module 7: Tapping and Threading
Module 7: Tapping and Threading Module Objectives After the completion of this module, the student will be able to:
1. Explain the tapping process.
2. Explain the threading process.
3. Differentiate between thread classes
4. Identify the tap types.
5. Explain the tapping and threading procedure.
6. Use the tapping and threading tools to create a tap and a
thread.
Module Contents
Topic Page No.
1 Introduction 3
2 Tapping 3
3 Threading 3
4 Hand threading safety 3
5 Threads standards 4
6 Internal Threading 5
7 Taps types 5
8 Tap Drill 6
9 Tap Wrenches 8
10 Care in tapping 8
11 Practical task 8
ATM-1022 – Mechanical Workshop
3 Module 7: Tapping and Threading
7.1 Introduction
One of the most effective ways to fasten two or more components is
through the use of screws or bolts, secured in properly threaded
holes. This method of fastening is more robust then other fastening
methods, allowing repeated assembly and dismantling via simple
screwing and unscrewing of the screw.
7.2 Tapping:
Tapping is the process of producing threads in a metal using
certain tools.
7.3 Threading
A thread is a spiral or helical ridge found on nuts and bolts.
Thread is specified by the diameter and the pitch (number of
threads per millimeter)
7.4 Hand threading safety
Chips produced by hand threading are sharp and should be
cleaned by using a brush or piece of cloth.
Do not use compressed air to remove the metal chips.
Newly-cut external threads are very sharp. Again use a
brush or cloth to clean them.
Wash your hands after using cutting fluids or oils.
Have cuts treated by a qualified person.
Be sure the die is clamped firmly in the die stock. If not, it
can fall from the holder and cause injury.
Broken tap have very sharp edges and are very
dangerous. An extra care should be taken in dealing with
broken taps.
ATM-1022 – Mechanical Workshop
4 Module 7: Tapping and Threading
7.5 Threads standards:
There are many types of threads used in different applications.
The most frequently used standard is the ISO standard that is
shown in the figure 7.1
Fig. 7.1 ISO screw pitch (F: crest, D: thread depth, P: thread
pitch)
Metric Size Pitch Tolerance
M 6 0.75 5g
An example of ISO metric tolerance is shown in figure 7.3
figure 7.3 ISO metric tolerance
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ATM-1022 – Mechanical Workshop
6 Module 7: Tapping and Threading
Threads are started with a taper tap. Then the plug tap is used
after the taper tap has cut threads as far into the hole as
possible. Finally threads are cut to the bottom of a blind hole
(one that does not go through the part) with a bottoming tap. It
is necessary to use the full set of taps, only when a blind hole is
to be made as illustrated in Fig 7.7
A: Open or through hole.
B: Blind hole that is
drilled deeper than
desired threads
C: Blind hole with
threads tapped to
bottom.
Fig. 7.7 types of threaded holes
7.8 Tap Drill
The drill used to make the hole prior to tapping is called a tap drill.
Theoretically, it should be equal in diameter to the minor diameter of
the screw that will be fitted into the tapped hole. Table (1) below
shoes the relationship between the thread normal size (diameter)
and the its proper tap drill diameter.
ATM-1022 – Mechanical Workshop
7 Module 7: Tapping and Threading
Figure 7.8 Threads dimensions
Normal size
(mm)
Tap Drill
(mm)
M3 x 0.5 2.50
M4 x 0.7 3.30
M5 x 0.8 4.20
M6 x 1.0 5.00
M8 x 1.25 6.70
M10 x 1.5 8.50
M12 x 1.75 10.20
Table (1): Thread and tap drill chart for metric threads.
Tap Drill = Normal size – thread pitch
ATM-1022 – Mechanical Workshop
8 Module 7: Tapping and Threading
7.9 Tap Wrenches
Two types of tap wrenches are available. The selection of tap
wrench depends on the tap size. A T-handle tap wrench is used
with all small taps while the Hand Tap Wrench is used with large
taps.
Fig. 7.9 Tap wrenches
Top: Hand tap wrench. Bottom: T-handle tap wrench
7.10 Care in tapping
Use the correct size tap drill
Use a sharp tap and apply sufficient quantities of cutting
fluids.
Start the taper tap square with the work.
Do not force the tap to cut.
Avoid running a tap to the bottom of a blind hole and
continuing to apply pressure.
Remove burrs on a tapped hole with a smooth file.
7.11 Practical task
Refer back to the drill gauge project to perform the required tapping
and threading. The following procedures have to be followed to
complete this task
1. Select the correct taps and tap wrench
2. Apply suitable cutting fluid to the tap
3. Place tap in hole as vertically as possible
ATM-1022 – Mechanical Workshop
9 Module 7: Tapping and Threading
4. Press downward on wrench, applying equal pressure on both
handles
5. If tap is not entered squarely, remove from hole and restart it
by applying pressure in direction from which tap leans
6. Turn tap clockwise one-quarter turn, and turn it backward
about ½ turn to break the chip (must turn with steady
motion)
7. Care must be taken not to tap too deep for a blind hole
8. When finished, clean hole and check with thread gage or
appropriate bolt
7.10 Drill gauge project
ATM-1022 – Mechanical Workshop
10 Module 7: Tapping and Threading
Student’s notes ...................................................................................................
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