Cotter Joint

For applications where the machine elements are to be detached whenever desired, temporary joints are used. Riveted and welded joints are permanent joints. Threaded fasteners are one type of temporary joints and are discussed in Chapter 16. Cotter joints are used to join two rods having tensile or compressive loads. They cannot be used, if the members rotate. A typical application of a cotter joint can be seen in a piston rod joined with a cross head of a steam engine and pedal crank of a bicycle (shown by arrow in Plate 12.1).

Types of Cotter Joints

• Sleeve and cotter joint

• Socket and spigot joint

• Gib and cotter joint Cotter

A cotter is a tapered machine element with a rectangular cross section of approximate width 1.3d (d is the rod diameter), thickness 0.3d, and length 4d. One edge is straight, while the other edge has a taper on the width of the order of 1:30 to 1:100. Sometimes, the edges of the ends are rounded. The thickness remains constant. Top and bottom edges are curved, with radius equal to d and this curved portion is tapered for thickness at 60° as shown in middle view of Figure 12.1.

Sleeve and Cotter Joint

This is the simplest method of joining two rods. Each end is enlarged in diameter and rectangular slots of about 1.4d × 0.3d are cut diametrically at a distance of 1.3d from the end. Both the rods butt each other and a sleeve of length 8d having similar slots at required positions is aligned (Figure 12.2).