Cam mechanisms convert rotary motion into reciprocal motion. A cam mechanism consists of a cam and a follower.

A cam is a shaped piece of metal attached to a rotating shaft.

A follower is a rod that rests on top of the cam, rising and falling as the cam rotates to create a reciprocating motion.

A cam mechanism will often include:

• a slide to stop the follower slipping

• a crank to rotate the camshaft

• a wheel follower between the cam and the follower to reduce friction

Types of cam

• Eccentric (circular): the pivot is off-centre, causing the follower to steadily rise and fall

• Pear-shaped: for half a turn, the follower remains stationary. Then it rises for a quarter rotation, and falls for the last quarter rotation.

• Snail: the follower rises then suddenly drops. This type of cam can only rotate in one direction

• Heart shaped (constant velocity): the follower rises and falls, never remaining stationary. For this reason, it is said to have constant velocity.