As an illustration of a cam of the latter character, we may
refer to the diagram, which shows a form very much used where

a small motion of a lever is re-
quired; the lever ACB is centred
T upon the point C, and will com-
] mence to move as soon as the
pin at the end A reaches that
portion of the ring which departs
from the circular form.
Note. — This kind of earn has the property of giving a motion
parallel to the axis upon which it is shaped.
Art. 69. — As an example of two cam grooves in juxtapositioi
one formed upon a flat plate and the other upon a cylinder, we
may refer to a machine which was formerly used for shaping coni-
cal box-wood plugs of the kind required for expanding an elon-
gated bullet into the grooves of a rifle.
Fig. 84.
m




Cams.
79-



Bullets of this class have a hollow recess at the base, into which
a plug is fitted, and when the powder is fired the thin sides of the
recess are forced into the grooves of the rifle by the action of the
plug. At the present time these plugs are made of compressed
clay, but formerly they were cut from a rod of box-wood by ma-
chinery.
The wood is first cut up into small square rods by means of
circular saws, and one of the wooden rods is fixed in a saddle,
as shown at H in fig. 85. Our drawing is taken from a lecture
diagram by Sir J. Anderson.
Fig, 85.
The next operation is to bring a revolving cutter, which
carves out the shape of the plug, upon the end of the rod H.
