CHAPTER 4
THREAD MANUFACTURING
OBJECTIVES
 At the end of this lesson, student will be able to:
 Explain the purpose of thread
 Name and explain parts on the thread
 Name and describe type of thread profile
 Describe methods to produce thread
Introduction to Threads
 A thread – defined as a helical or spiral ridge of uniform section
formed on the outside or inside of a cone or a cylinder.
 The purposes of thread are:
For fastening devices such as screws, bolts, studs, and nuts.
To provide accurate measurement as in a micrometer.
To increase torque. Heavy work can be raised with screw jack.
To transmit motion. The threaded lead screw on lathe causes the
carriage to move along during the threading process.
To provide clamping force.
Parts of Major
thediameter
Thread
– the largest diameter of
an external or internal thread.
Minor diameter – the smallest diameter of
an external or internal thread.
Pitch – a distance from a point one thread
to the next thread, which measure parallel
to the axis.
Root – a bottom surface joining the sides
of two adjacent threads.
Crest – a top surface joining two sides of
thread.
Angle of thread – an angle between the
sides of a thread measured in an axial
plane.
Types of thread profile

There are five common types of thread profile:
1.
2.
3.
4.
5.



V-thread
Trapezoidal thread (Acme thread)
Saw tooth thread
Knuckle thread
Square thread
Clamping screws have V-thread.
For moving screws, Trapezoidal, saw tooth and round thread are
suitable.
For moving screw with small pitch (measuring spindle)
frequently V-thread are used.
V-thread
Trapezoidal thread
(Acme thread)
Saw tooth thread
Square thread
Knuckle thread
Direction of thread
 Direction of thread can be
right- or left- hand direction.
 Right-hand thread is widely
used.
 Right-hand thread – a nut is
screwed on a bolt in clockwise
direction.
 Left-hand thread – a nut is
screwed on a bolt in
anticlockwise direction.
Thread Manufacturing

Screw thread can be produced in many methods such as:
a)
b)
c)
d)
e)
f)


Taps.
Dies and die stocks either by hand or machine.
Threading tooling on lathe machine.
Milling.
Grinding.
Rolling.
Threads can be also manufactured by pressing or casting.
To produce the thread, it will depend on the number of
workpiece and the desired quality and the surface quality.
Taping and Dieing
Taps
 Taps are cutting tools used to cut internal threads. They are
made from high-quality tool steel, hardened and ground.
 The most common hand taps are called taper or first, plug or
second, and bottoming taps
Tapping
 Tapping is the process of cutting an internal thread with a
tap.
 Before tapping the following should be determined:
 The proper tap hole has been drilled.
 The tap has the correct specifications.
 The tap hole is clean and free of all chips (particularly for
blind holes).
 A suitable cutting fluid has been selected for application
during the tapping process.
 Hand tapping should be performed by
having both hands on the handle and equal
pressure applied to rotate the handle.
 The tap will then tread itself into the hole.
To break the chip and to avoid loading the
tap with material, the tap should be
backed off about a half a turn for each
complete thread formed. This is to ensure
the tap can be easily removed from the
work.
 On completion the tap is backed out of the hole, all chips are
blown clear; and the threads are checked with a thread gage.
 If the thread is too tight, "chase" the threads by running the
tap through again until it meets specifications.
 There are two tapping tools used to turn the tap and form
the threads, the T-handle is used for the smaller tap sizes and
the Tap Wrenches.
Tap Wrench
T-handle
Dieing
 Dieing is a process of cutting external thread on cylindrical




part using a die.
The die sizes are available up to 36mm in thread diameter.
The circular split die is commonly used and the process is
done manually.
Dies are made from high-speed steel hardened and tempered
and split in one side to allow the small adjustment of size
during the dieing process.
The die is held by using a holder which is called die stock.
Die
Center screw to
open die
Die Stock
Thread Cutting on Lathe
 Thread cutting with taps and dies on lathe.
 By using the lathe machine, threads can be produced by using
tapping, dieing and the threading tools. This method is very simple
and cheap.
Internal thread cutting
with the tap
External thread cutting with
the threading die
Cutting screw threads
Thread Milling
 The most common thread profiles with exception of the square
thread can be manufacture economically by thread milling.
 It is distinguished between long thread milling and short thread
milling.
External long thread milling
Long thread milling machine
Thread Grinding
 Thread grinding is a finishing operation and is applicable for heat-
treated to eliminate possible errors resulting from heat
treatment.
 Thread grinding is selected, when high accuracy and high
surface quality are required.
 Normally it was applied for the finishing of taps, thread plug
gauges, ring screw gauges, measuring screws and other precision work.
 Single and multiple profile grinding wheels are used for grinding
Thread grinding
Thread Rolling
Thread rolling is a forming process. Material is rearranged
to create the desired form. As a result, the workpiece
blank grows after the rolling operation.
THANK YOU……