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242 Making Things Move

constant radius is called the dwell, because the follower just FIGURE 8-4 Edge cam
dwells there and doesn’t create motion. The shape of the with lobe and dip
follower is important. A finer point on the follower will be
more able to track intricate variations on the cam, but will
need to be strong enough to survive the stress of riding in
and out of all those bumps (see www.flying-pig.co.uk/
mechanisms/pages/cam.html). Using a bearing or roller on
the end of the follower is a good way to decrease this stress
by decreasing friction. A bigger cam will give you more
leverage to push on a follower and be easier to turn than a
small one trying to do the same job, so don’t try to do too
much with a small cam.

Face and Drum Cams
A face cam (also called a radial or plate cam) transfers motion to a pin or roller free to
move in a groove on its face. These are usually designed to operate in both directions,
and create a positive-drive situation in both directions because the follower is
contained in the groove of the face cam.

A drum cam (also called a barrel or cylindrical cam) has a path cut around its outside
1
edge in which the roller or follower sits. It creates a back-and-forth motion on the
follower in a plane parallel to the axis of the cam.
Figure 8-5 shows both of these cam profiles. Face and drum cams are less popular and
harder to make at a hobbyist level, but are included here to show you the possibilities.

FIGURE 8-5 Face cam (left) and drum cam (right)