and are made in halves, as shown in the figures and also in Figures 270
and 271, which represent cams removed from the other mechanism. To
enable a certain amount of adjustment of the cams upon the collar, the
bolts which hold them to the collar fit closely in the holes in the
collar, but the cams are provided with oblong bolt holes as shown, so
that the position of either cam, either with relation to the other cam
or with relation to the crank-pin, can be adjusted to the extent
permitted by the length of the oblong holes.

[Illustration: Fig. 269.]

The crank is assumed in the figures to be on its dead centre nearest to
the engine cylinder, and to revolve in the direction of the arrows. The
cams are so arranged that their plain unflanged surfaces bolt against
the collar.

The method of drawing or marking out a full stroke cam, such as C in
Figure 267, is illustrated in Figure 272, in which the dimensions are
assumed to be as follows:

Diameter of crank shaft, 7-1/2 inches; travel of cam, 3 inches; width of
yoke, 18 inches.

[Illustration: Fig. 270.]

The circumference of the cam is composed of four curved lines, P, P', K
1, and K 2. The position of the centre of the crank shaft in this
irregularly curved body is at X. The arcs K 1 and K 2 differ in radius,
but are drawn from the same point, X, and hence are concentric with the
crank shaft.

The arcs P, P', are of like radius, but are drawn from the opposite
points S, S', shown at the intersection of the arcs P, P', with the
arc K 1. Thus arcs P, P', are eccentric to the crank shaft.

[Illustration: Fig. 271.]

[Illustration: Fig. 272.]

[Illustration: Fig. 273.]

To draw the cam place one point of the dividers at X, which is the
centre of the crank shaft, and draw the circle E equal to width of yoke,
18 inches. Through this centre X, draw the two right lines A and B. On
the line B, at the intersection of the curved line E, draw the two
vertical lines A 1, A 1. With a radius of 10-1/2 inches, and with one
point of the dividers at X, draw the arc K 1. With a radius of 7-1/2
inches, and one point of the dividers at X, draw the arc K 2. With a
radius of 18 inches, and one point of the dividers at the intersection
of the arc E, with the vertical line A 1 at S, draw the arc P opposite
to S, and let it merge or lose itself in the curved line K 2. Draw the
other curved line P' from the other point S, and we have a full stroke
cam of the dimensions required, an