Threads and Its Types
Thread plays a very important role in the engineering line for manufacturing various items of daily use. In this engineering and scientific age, machines are used every moment at every stage. Without threads, most of the machines cannot be used.
Definition of Threads
Spiral grooves of equal measurement or shapes made on
a round cylindrical article or pipe are known as threads. In other words, spiral grooves of equal pitch and equal
depth made on the parallel round cylindrical surface
or conical round surface are called threads.
For example, if we take a round stick and wind a piece
of wire in angular indication, the wires twist
would move ahead on the round stick. The path on which the wire moves
ahead is called Helix. Like this helix, the thread is inclined in an angle on a round surface. Threads may be internal or external.
As already mentioned above, the shape or size of
threads depends upon their utility. Thread cutting tools are also made accordingly. According to their shapes.
Types of Threads
Following are the 13 different types of
threads:
1. Right-hand threads
2.
Left-hand threads
3.
taper threads
4.
"V" shape threads
5. Metric or International Threads
6.
British Standard
Threads
7. Seller Threads
8.
Square Threads
9.
Acme Threads
10.
buttress Threads
11.
Knuckle Threads
12. Worm Threads
13.
Single and Multi-Threads
Ø Left Hand Threads
These threads are inclined towards the left hand. These are tightened in anticlockwise movement. For example, on a screw with left-hand threads, threads are so cut that the bolt, screw, or nut has to be turned in a counter-clockwise motion to engage or tighten it. Their use is comparatively less.
Ø Taper Threads
Threads cut on around but taper surface is called
taper threads. These are sued for shafts like buffing spindles. These threads
can be right hand or left hand.
The above threads are used for the following purpose:
1.
To join two parts of a machine like nut-bolt and stud.
2.
To get mechanical livers
for lifting weights,
such as chain pulleys, jacks etc.
3. For accuracy
in precision instruments like micrometers.
4.
In jobs of power transfer.
5. To control or reduce speed.
Ø "V" Shape Threads
This type of threads is in the shape of the English alphabet "V". It is most widely used. These types of threads can be cut or made by tap, die, lathe machine and milling etc. These threads are made of different standards. The following types are mostly used.
Ø Metric or International Threads
These types of the thread were originally adopted in
1898 to 1908 in central France. With the passage of time, other international countries also started using it. The
Indian standards institute has also adopted this thread.
These threads are made on jobs of 0°25 mm to 300 mm in
diameter. Its angle is at 60°. Its screw is flat and the root is round. According to I.S. 1330-1958, these are
written prior to the letter M and figure written
after "M" indicates pitch such as -M20 X 2.5. It means the number of
threads is 20 per inch and its pitch is 2.5 mm.
Thread Angle = 60° Crest and root = 0. 125
X pitch
Pitch
=1/T.P.I. (in mm)
Ø British Standard
Whitworth Threads
This type of threads is originated from great Britain.
sir joseph Whitworth, a citizen of Great Britain invented this thread in 1841. This thread was to provide the
facility of interchangeability. It is used in
ordinary nut-bolts and other jobs. Its angle is 55°. Its crest, as well
as root, is in round shape. It's known as B.S.W. Thread.
· Thread angle=
55 °
· Pitch = 1/T.P.I
· Depth = Pitch X 0.6403
· Radius = Pitch X 0.1373
· Core dia. = D- (1.28 X Pitch)
· (D= outer dia. of bolt)
Ø British Standard
Fine Thread
In shape, this thread is similar to B.S.W. thread. The angle of this thread is also 55° but the number of thread per inch is more i.e. the thickness of threads is less. This makes the grip stronger. Nut bolts having this thread are used where is more vibration.
Ø British Association Threads
This type of thread is of every think make-up. It is
used in small and tiny electrical and mechanical instruments like radio, television, electrical goods, meters and
watches. The angle of these threads is 47 1/2°. These can be used for 1/2" or 6 mm nut bolts.
These are recoghinsed through numbers, which range between
0 to 12. number 0 = 0. 236" or 6 mm.
Number 12 = 0.0511" or 1.3 mm.
· Thread Angle = 47 1/2"
· Depth of thread = 0.6
X Pitch
· Pitch = 1/T.P.I
· D = 1.36 X Pitch
Ø Seller Threads
· Thread Angle = 60°
· Depth of thread = 0.649519
X Pitch
· Dia. = 0.866025 X Pitch
· Crest = D/ 8
· Root = 0.125 X Pitch
Ø Square Threads
This thread has a very powerful root. ITs make up is
square. These threads are used for lifting heavy loads, transfer of power, to exert pressure, screw jack, lead
screw of machines, press machines and vice spindle instruments. Their specific measurement and number per inch are not fixed.
· Thread Angle = 90°
· Depth of Thread
= 0.5 X Pitch
· Crest and Root = 0.5 X 5
Ø Acme Threads
These threads are more or less like square threads but
their shape is in taper i.e. flat from bottom and thin from the top. It is comparatively easier to cut it on a
job than the square threads. IT is also considered
stronger. AS these threads have slanting ends, it is easier to fix or unscrew
the split nut on it. There is no backlash
in it. This thread is made at 29°
angle.
· Thread Angle = 29°
· Depth of Thread = 0.5
X Pitch + .01"
· Crest = 0.3707 X Pitch
· Root = 0.33707 X Pitch - 0.0052"
Ø Buttress Threads
· Root and crest = 0.125 X Pitch
· Thread Angle = 45°
· Depth = 0.75 X Pitch
Ø Knuckle Threads
This
thread is also very strong. It is
used in heavy and light jobs of rough nature. This is half round at both root and crest.
It can be cast in a mold.
· Depth of Thread= 0.5 X Pitch
· Root and crest Radius
= 0.25 X Pitch
· These threads
are specially used for coupling
of rali-coaches.
Ø Worm Threads
Their shape is almost similar to Acme Threads but
these are deeper than Acme threads. Their angle is also at 29 °. This thread is used in worm wheel of motor
vehicles for the transfer of power at 90°. As
three teeth of worm wheel fit into the shaft with worm threads, they fit well.
· Thread Angle = 29°
· Depth of Thread
= 0.6866 X Pitch
· Root = 0.32 X Pitch
· Crest = 0.335 X Pitch.
Ø Single and Multi-Threads
In a piece of work, it is possible to have some
separate and independent threads running along with it. Thus, there are a single-threaded screw and multiple or
multi-start threaded screw. The independent threads are called starts,
and we may have single-start, two-start, three-start, etc.
For one complete turn round the screw or bolt then there is a movement of one thread the screw is called a single-threaded screw. And when there is a movement of more than one thread, the screw is called multiple or multi-start threaded screws.
In the case of a three-start thread, for one complete turn, the thread advances three times as far if it were a single thread. Multi-start threads are used in those cases where fast movement or motion is needed Fountain where they are widely used.
References:
1.
https://www.theengineerspost.com/types-of-threads/
2.
https://dimide.com/blogs/why-dimide/clamp-thread-types-their-benefits
Vishwakarma Institute of Technology, Pune
Division: Mechanical SEDA
Batch 1_Group 4
Under the guidance of: Prof. S.R. BAHULIKAR
Group Members: |
- Niraj Hemant Kurane
- Prakash Bira Solankar
- Aashish Vinod Tupe
- Anurag Vasantrao Jadhav
- Rohan Ratnadip Pawar
- Anurag Balasaheb Warale
Informative content
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