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240 Making Things Move

Cams and Followers
Cams are useful any time you have one or more objects you want to move in a periodic
or irregular motion. In the most basic terms, a cam is any eccentric or noncircular shape
that can convert rotary motion into linear motion. Cams open and close the valves on
modern internal combustion engines. They are used extensively in the mechanical toys
we’ll talk about later in the chapter.

You can make cams yourself from wood if you have some basic tools, or find them off
the shelf from WM Berg (www.wmberg.com) and other suppliers. The party sheep
shown later in Figure 8-17 uses a cam attached to the rotating shaft inside to make its
head nod.
Edge Cams
The most basic type of cam is called an edge (also disk or peripheral) cam (see Figure 8-2).
The part that the cam moves is called a follower. The edge cam transfers motion to
a follower moving against its edge. This is a friction-drive system because there is
nothing locking the cam and follower together. Edge cams can be used to create
linear (translating) motion or oscillating rotary motion.

The difference between the highest point on the lobe and the minimum radius on the
cam is called the throw, and is the maximum amount of linear motion the cam can

FIGURE 8-2 Edge cam with translating follower (left) and with oscillating follower (right)