Cotter Joint
By SY Mech C, Batch 2 Group 4
Under the guidance of
Prof. Shrinivas Chippa
DEPARTMENT OF MECHANICAL ENGINEERING
VISHWAKARMA INSTITUTE OF TECHNOLOGY
( An Autonomous Institute, Affiliated to Savitribai Phule Pune
University)
Table of Content
Sr.no Tittle Page.no
1 Introduction 3
2 Types Of Cotter 5
Joint
3 Failures Of Cotter 8
Joint
4 Application Of 9
Cotter Joint
5
6
Introduction :
One of the temporary joining methods is a cotter joint. In a cotter joint, two
coaxial rods are joined using two components, socket, and spigot. One rod
is fitted with a spigot and this assembly is fitted into a socket on one end of
another rod. There is a slot in the socket and spigot to accommodate a key.
These slots are aligned so that the key can be inserted to lock the two rods
together.
Cotter joints are used to support axial loads between the two rods, tensile
or compressive.
Although a cotter joint will resist the rotation of one rod relative to the other,
it should not be used to join rotating shafts. This is because the cotter will
not be balanced and may work loose under the combination of vibration
and centrifugal force.
A typical cotter joint assembly is made of three components
• Spigot: A spigot is a solid cylindrical profile, having a slot for the cotter to
be inserted. On the neck of the spigot, we can see a collar. This collar
allows the spigot to form a clearance at the end of the socket cavity. Also,
the collar is useful in aligning the cotter slots in the spigot and socket.
• Socket: A socket is a hollow cylindrical profile, having a slot for the cotter
to be inserted.
The spigot cavity has the dimensions of the spigot to accommodate the
spigot through it.
• Cotter: It is a wedge-shaped piece of metal acting as a key for the joint.
The cotter connects two parts i.e. spigot and socket, which are
non-rotating.
Reason for Tapering of Cotter Joint : There are two benefits of it: First, this
tapper is easy to remove and makes disassembling of joint a simple
process. Second, the tapper also ensures the tightness of the joints and
prevents the parts from loosening.
The specific taper value in a cotter joint is determined based on various
factors, including the application requirements and the materials used. The
most common taper ratio used in cotter joints is "1 in 24" or "1 in 48." This
means that for every 24 or 48 units of length, the cotter width reduces by 1
unit.
Types of Cotter Joint:
The types of cotter joints are distinguished based on the alignment and
technique employed by the cotter for interlocking the rods. h
Following are the three types of cotter joint to connect two rods by a cotter:
• Socket and spigot cotter joint
• Sleeve and cotter joint
• Gib and cotter joint
Socket and Spigot Cotter Joint
Two coaxial rods are joined temporarily by means of a socket and spigot.
The assembly of the joint is such that the socket is provided on one end of
the rod and the other end of another rod is inserted into. the socket. The
end of the rod is put into a spigot.
A cotter joint known as a socket and spigot joint, is a method of temporarily
joining two coaxial rods, one end of the rod provided with a socket type and
the other end of the other rod inserted into the socket. The end of the rod
goes into a socket also called a spigot.
Sleeve And Cotter Joint:
The sleeve and cotter joint is the simplest cotter joint. The assembly is
simple and is very convenient to build and dismantle. With regards to the
load-bearing ability, the joint is rigid due to the sleeve overlapping through
both the connecting rods: It can bear both tensile and compressive loads,
though it is not suitable to undergo rotation.
The sleeve over the rods prevents the angular misalignment of the rods.
This method of cotter joint is used to typically assemble two similar coaxial
rods. The assembly includes a sleeve and two cotters with tapered
wedge-shaped geometry. There are sections made into the sleeve to make
provision for the cotter to be inserted.
Gib and Cotter Joint:
A Gib and cotter joint is used to connect rods with rectangular or squared
cross-sections. The socket in this joint is a profile with open walls making it
a fork-like structure also known as the strap. If the joint is made without the
gib, the cotter experiences friction with the strap causes it to deform
outwards. In order to prevent this. Gib is used to hold the strap ends
together.
The Gib also provides a larger bearing surface for the cotter to slide as the
bearing power is increased. It causes the friction to increase, in turn
reducing the slack back.
A Gib is like a cotter but with two gib head profiles at its ends. The
thickness of the gib and cotter is the same. Sometimes to prevent
loosening of the cotter, a small set screw is used through the rod jamming
against the cotter
To prevent this, Gib is used to hold the ends of the strap together. In
addition, the gator provides a larger bearing surface for the cotter to slide
as the holding power increases. Thus, the friction of the cotter reduces the
tendency to slack back
Failures Of Cotter Joint :
1. Shear Failure: One of the primary failure modes of cotter joints is shear
failure. When the it is subjected to excessive forces or loads, the cotter
pin may fail due to shearing along its cross-sectional area. This can
occur if the cotter pin is not properly sized or if the joint is subjected to
forces beyond its intended design limits.
2. Fatigue Failure: Cotter joints that experience repeated cyclic loading or
vibrations can be prone to fatigue failure. Over time, the constant
loading and unloading cycles can weaken the material of the cotter pin,
leading to crack initiation and propagation. This can ultimately result in
the failure of it.
3. Wear and Loosening: Continuous movement and rubbing between the
cotter pin and the surrounding components can cause wear. This wear
can lead to the loosening of the joint, reducing its effectiveness and
potentially causing failure. Regular inspection and maintenance are
essential to identify and address any signs of wear or loosening.
4. Misalignment: If it is not properly aligned during assembly, it can result
in stress concentrations and uneven distribution of forces. This
misalignment can lead to premature failure of the joint as the cotter pin
may experience excessive forces in certain areas, causing it to fail or
deform.
5. Corrosion: Cotter joints that are exposed to corrosive environments or
lack proper corrosion protection can suffer from corrosion-related
failures. Corrosion weakens the metal of the cotter pin, reducing its
strength and integrity. This can result in unexpected failure of the joint,
especially in applications where the joint is exposed to moisture,
chemicals, or harsh environmental conditions.
Possible Modes of Failures of cotter Joint
Tensile Failure of Rods :
Each rod is subjected to a tensile force P.
Tensile stress in the rods =
where [σ] = allowable tensile stress for the material selected.
Tensile Failure of Spigot :
Area of the weakest section of spigot resisting tensile failure =
\[\left[ {\frac{\pi }{4}d_2^2 - {d_2}t} \right]\]
Tensile Stress in the Spigot =
Tensile Failure of Socket :
Area of the weakest section of socket resisting tensile failure =
\[\left[ {\frac{\pi }{4}(d_1^2 - d_2^2) - \left( {{d_1} - {d_2}} \right)t} \right]\]
Tensile Stress in the Socket =
Shear Failure of Spigot End :
The spigot end is subjected to double shear.
Total area that resists the shear failure = 2ad2
Shear Stress in the socket =
where [\[\tau\]] = allowable shear stress for the material selected.
Shear Failure of Socket End :
The socket end is subjected to double shear.
Total area that resists the shear failure
Shear Stress in the socket =
Crushing Failure of Spigot End :
Area under crushing \[= {\text{t}}{{\text{d}}_2}\]
Crushing Stress =
where [σc] = allowable compressive stress for the material selected.
Crushing Failure of Socket End :
Area under crushing \[= \left( {{d_4} - {d_2}} \right)t\]
Crushing Stress,
Shear Failure of Spigot Collar :
Area of spigot collar that resists the shear failure = \[\pi\] d2 t1
Shear Stress in the socket =
Crushing Failure of Spigot Collar :
Area of spigot collar under crushing = \[\frac{\pi }{4}(d_3^2 - d_2^2)\]
Crushing Stress =
Shear Failure of Cotter :
The cotter is subjected to double shear.
Total area of cotter that resists the shear failure = 2bt
Shear Stress in the pin =
Application of Cotter Joint:
A cotter joint is used to support the axial load between two coaxial rods,
which are the tensile and compressive loads. Although a cotter joint will
resist the rotation of one-rod relative to the other, it should not be used to
join a rotating shaft.
● This joint is used between the piston rods and the tail of the
pump rods.
● Cotter’s joints are used between the slide spindles and the fork
of the valve mechanism.
● Arrangement of cotter and dowel to join two parts of a flywheel.
● Foundation bolts: mainly used in fastening heavy machines for
foundations and construction
● In an automobile engine, a cotter joint is used to connect the
extension of the piston rod with the connecting rod in the
crosshead.
● The cotter joint has historically been used to connect connecting
rods to steam engines and pumps for the extraction of mines.
● It is used in a bicycle to connect the paddle to the sprocket
wheel.
● Use a wet air pump to join a tail rod with the piston rod.
● It is used to connect two rods of equal diameter subjected to
axial forces.
Conclusion:
