A cam is generally a disc or a cylinder mounted on a
rotating shaft, and it gives a special motion to a follower,
by direct contact. The cam profile is determined by
the required follower motion and the design of the
type of follower.
The motions of cams can be considered to some
extent as alternatives to motions obtained from linkages,
but they are generally easier to design, and the resulting
actions can be accurately predicted. If, for example, a
follower is required to remain stationary, then this is
achieved by a concentric circular arc on the cam. For
a specified velocity or acceleration, the displacement
of the follower can easily be calculated, but these
motions are very difficult to arrange precisely with
linkages.
Specialist cam-manufacturers computerize design
data and, for a given requirement, would provide a
read-out with cam dimensions for each degree, minute,
and second of camshaft rotation.
When used in high-speed machinery, cams may
require to be balanced, and this becomes easier to
perform if the cam is basically as small as possible. A
well-designed cam system will involve not only
consideration of velocity and acceleration but also the
effects of out-of-balance forces, and vibrations. Suitable
materials must be selected to withstand wear and the
effect of surface stresses.
Probably the most widely used cam is the plate
cam, with its contour around the circumference. The
line of action of the follower is usually either vertical
or parallel to the camshaft, and Fig. 24.1 shows several
examples.
Examples are given later of a cylindrical or drum
cam, where the cam groove is machined around the
circumference, and also a face cam, where the cam
groove is machined on a flat surface.
Manual ofEngineering Drawing
Second edition
Colin H Simmons
I.Eng, FIED, Mem ASME.
Engineering Standards Consultant
Member of BS. & ISO Committees dealing with
Technical Product Documentation specifications
Formerly Standards Engineer, Lucas CAV.
Dennis E Maguire
CEng. MIMechE, Mem ASME, R.Eng.Des, MIED
Design Consultant
Formerly Senior Lecturer, Mechanical and
Production Engineering Department, Southall College
of Technology
City & Guilds International Chief Examiner in
Engineering Drawing
