When there is a requirement of a small amount of flexibility or angular moment, Knuckle joint is used.  A knuckle joint is used to connect two rods which are under a tensile load. In this article, I am going to present a detailed design procedure for Knuckle Joint and Cotter Joint.

The Design Procedure for Knuckle Joint is Made to Calculate:

  • The outside diameter of eye or fork (mm)
  • The thickness of each eye.
  • The enlarged diameter of each rod by an empirical relationship.
  • Diameters of the pin by shear considerations.
  • Bending considerations.

Specifications for Knuckle Joint:

  • Outside diameter of eye or fork(mm) = d0
  • The thickness of each eye or fork (mm)= a
  • The thickness of the eye end of rod = b
  • Diameter of Knuckle Pin(mm)= d
  • The diameter of Pinhead= d1
formulas of knuckle joint

The detailed explanation for the Design Procedure for Knuckle Joint is shown below in the form of video.

Cotter Joint: 

Cotter’s joint is used to connect two rods subjected to compressive or axial tensile loads. It is not at all suitable to connect rotating shafts which transmit torque.

Cotter’s joint is widely used to connect the piston rod and crosshead of a steam engine, as a joint between the piston rod and the tailor pump rod, foundation bolt, etc.

The Design Procedure for Cotter Joint is Made to Calculate:

  • The diameter of each rod
  • The thickness of the cotter by an empirical relationship
  • The diameter of the spigot on the basis of tensile stress
  • Shear failure
  • Crushing failure of spigot etc.

The formulas required for the cotter joint to calculate the above conditions are shown below:

formulas of cotter Joint

The remaining part for the design procedure of a cotter joint is presented in the form of a video which is shown below.

This is the complete explanation of the Design Procedure for Cotter Joint and Knuckle Joint which is shown in a detailed manner. If you have any doubts, feel free to ask from the comments section. Please Share and Like this blog with the whole world so that it can reach to many.


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Mohammed SHAFI

Mr. Mohammed Shafi is an Assistant Professor at Sreenidhi Institute of Science & Technology. By education, he is a Mechanical Engineer and expertise in CAD & CAM. Mechanical Students is his first...

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