Cotter Joint: Definition, Types, Applications

The mechanical process comes easy and comfortable using a cotter joint

If you have a mechanical workshop, you need to make a joint of two parts like two rods. The joint work of two rods needs an effective method named by cotter joint.

If you are a professional worker then definitely you will have sufficient experience how to do the joint work but without an experience, the work of cotter joint is very difficult.

As a beginner, you should have valuable knowledge about it. So before you come to start knowing the same, just have a look at the details mentioned below starting with defining cotter joint.

What is a cotter joint?

A cotter-based joint comes with another name a socket or spigot joint. It comes with a method of temporarily joining between two coaxial rods and out of two rods; one is fitted with a spigot that fits inside a socket on one end of the other rod.

These joints are used to give support axial loads between the two rods, compressive or tensile.

A cotter-based joint will resist the rotation of one red relative to another but it should not be used to join rotating shafts.

The Cotter-based joint assembly consists of three components that are given below-

• Spigot – It is the male part of the joint and it has a rectangular slot for passing the cotter through itself. The spigot has a collar that rests on the socket end.
• Socket – It is the female part of the joint and it comes with a rectangular shape or slot for passing the cotter through itself. It has a circular hole and inside it, a spigot comes to be fitted.
• Cotter – It looks like a wedge-shaped piece of metal that connects two parts in a non-rotating way.

A cotter is a flat wedge-shaped metal piece and it is used to connect two rods that transmit the force without rotation.

The force may be axial, tensile, or compressive. The cotter is fitted in the tapered slot and it remains in its position for wedge action.

The value of taper on the cotter is 1 in 48 to 1 in 24. It provides two benefits. The first one provides the tapper easiness to remove and makes disassembling of joints a simple process and the second; tapper ensures the tightness of the joints preventing the parts from loosening.

Types of Cotter Joint 

Generally, three cotter joint types are available to connect two rods through a cotter.

• Socket and spigot cotter joint
• Sleeve and cotter joint
• Gib and Cotter joint

Socket and Spigot Cotter Joint –

A cotter joint comes with the name of socket & spigot joint. It is a method of temporarily joining two coaxial rods.

One end rod comes with a socket type and another rod comes with insertion into the socket. The end of the rod goes through a socket called a spigot.

A rectangular hole is made into the socket even in a spigot. The operation of a cotter goes through a hole to make a temporary connection between the two rods.

The load plays a role in acting axially but it changes its direction. The cotter-based joint makes designed to carry both tensile and compressive loads.

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Sleeve & Cotter Joint –

The sleeve and cotter joint come to a type of joint used typically connected to two similar coaxial cylindrical rods.

It includes a sleeve and two wedge-shaped tapered cotters. Appropriate slots cut the sleeve and cylindrical rods.

The cotter is mounting in these slots. The taper of the cotter is usually 1 in 24 and it is very important to know that the tapper sides of the two cottars must be connected.

The clearance is adjusted and when the coaters are driven on two roads, they come close to each other and make the joint tight.

Sleeve & cotter joint is a very simple joint in existence. It is quite rigid and can take both tensile and compressive loads.

It can be assembled and dismantled easily. The joint can also be used to connect pipe-looking tubes.

Rectangular rods and different-shaped cylindrical rods cannot be connected using this joint.

A sleeve and cotter joints are not allowed for angular misalignment between its cylindrical members. It cannot connect cylindrical members.

Sleeve and Cotter Joint Application-

Here are some applications of the same-

• For tensile load
• For compressive load
• Connecting pipe–locking tube

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Gib & Cotter Joint –

A Gib and cotter-based joint comes to be used at the strap end or big end of a connecting rod. In some cases, a cotter runs alone.

The friction between its ends causes the edges of the strap to open outward. To prevent this, Gib comes to be used to hold the ends of the strap together.

Moreover, the Gib and the cotter joints are used for the square-shaped or rectangular-shaped rod.

The end of one rod comes to be fitted at the end of the other rod that is made in three conditions mentioned below:

1.  When one gib is used, the cotter with one tapered and gib is always on the outside.
2. When two gibs are used and the cotter with both sides tapered
3.  If a small set screw is used through the rod jamming against the cotter.

Gib and Cotter Joint Application-

Here are some applications of the same-

• Strap end of connecting rod
• Big end of the connecting rod
• Holding strap end

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Function of cotter joint-

The function of the cotter joint is to firmly connect two rods that convey force or motion without rotating. Between a steam engine‘s crosshead and piston rod, it serves as a junction.

Failure of cotter Joint-

There are Several Methods of failure in cotter joint, given below-

• Failure of rod in tension
• Failure of the socket in tension across the weakest section
• Failure of the spigot in tension across the weakest section
• Failure of spigot rod and cotter pin in crushing
• Failure of cotter pin in shear
• Failure of socket collar in shearing
• Socket & spigot collar in crushing
• Failure of the spigot ends in shearing
• Failure of spigot collar in shearing

Application of Cotter Joint

For various purposes, uses of cotter joint are mentioned below-

• For connecting piston rods in a steam engine
• To connect the piston rod with its extension
• In bicycles, connect pedals to sprocket wheels
• In the case of foundation bolts
• In the joint between the slide spindle and the fork of the mechanism based on the valve
• To join the two halves of a flywheel.
• For joining of a tail rod with the piston rod in a wet air pump
• To connect two rods of equal diameters to axial forces
• To connect the piston rods’ extension in an automobile engine
• For connecting rods in stream engines and pumps for draining mines.

Advantages of Cotter Joint

• A cotter-based joint can be easily designed and parts easily occupy the same relative position after reassembly.
• The particular joints come to be joined in similar pipes, and tubes and even do not require special efforts.
• The process of assembling and dismantling cotter joints and related parts is easy and quick.
• The manufacturing process of these joints is simple and easy.
• It is completely rigid.

Read Also- Riveted Joints: Definition, Types, Uses, Efficiency, Advantages and More

Disadvantages of Cotter Joint 

• You will have a problem in the case of rectangular and dissimilar cylindrical rods as they cannot be connected using this joint.
• Rectangular rods and dissimilar cylindrical rods cannot be connected using this joint.
• The sleeve and cotter joints that cannot connect cylindrical members undergo rotation.

Know the process perfectly and use cotter joint according to your needs. I hope you enjoyed being here and gained some valuable knowledge. Consider sharing with friends and colleagues.

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Abhishek Tiwary

Abhishek Tiwary is a blogger by passion and a Quality Engineer by profession. He completed his B.Tech degree in the year 2017. Now working in a reputed firm. He loves to share his knowledge with others.