Cams and followers

A cam mechanism has two main parts:

  • a cam - attached to a crankshaft, which rotates
  • a follower - touches the cam and follows the shape, moving up and down
A cam mechanism showing directional arrows to demonstrate a crankshaft which rotates and a follower which moves up and down.

Cams

Cams can be produced in any shape, but the most common shapes are:

Circular

Circular cams use an off-centre pivot to cause the follower to move up and down. The follower will rise and fall by a reasonably large amount. These can be seen in pistons, for example on steam engines.

Circular cam, a follower and slide. Directional arrows show the movements of the cam and follower in the slide.

Pear

Pear cams are called this as they have the shape of a pear. It remains stationary for half a turn then gently rises and falls. These are used to make carousel horses rise and fall.

Pear cam, a follower and slide. Directional arrows show the movements of the cam and follower in the slide.

Snail or drop

Snail or drop cams have the appearance of a snail shell. It causes the follower to remain stationary for half a turn before gently rising and suddenly falling. They can only work by rotating in one direction. They are used on production lines to make regular holes or cuts in an item as it rotates and drops at regular intervals.

Snail cam, a follower and slide. Directional arrows show the movements of the cam and follower in the slide.

Heart-shaped or constant velocity

Heart-shaped cams or constant velocity cams have a shape similar to a heart. The follower rises and falls steadily with uniform velocity. There is no stationary period.

Heart-shaped cam, a follower and slide. Directional arrows show the movements of the cam and follower in the slide.

Followers

The purpose of a cam is to move a follower up and down. There are three main types of followers:

Flat

Flat followers have a flat bottom that sits on the cam. These cope well under load but aren’t very accurate and have a lot of friction.

Flat follower sitting on a pear cam. The flat follower is a tube with a flat bottom. Directional arrows show the movement of the flat follower and the pear cam.

Point or knife

Point or knife followers have a narrow point that sits on the cam. These are very accurate and low friction but are quick to wear away the pointed edge.

Point follower sitting on a pear cam. The point follower is a tube with a pointed bottom. Directional arrows show the movement of the pointed follower and the pear cam.

Roller

Roller followers have a roller such as a ball bearing attached to the bottom of the following. These are accurate, low on friction and can withstand load, but are more costly to produce.

Roller follower sitting on a pear cam. The roller follower is a tube with a ball at the bottom. Directional arrows show the movement of the ball follower and the pear cam.