the arcs P, P', with the arc K 1. Thus arcs P, P', are eccentric to the crank shaft.

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

18

Fig. 273.

With a radius

the dividers at X, draw the arc K 1. of 71⁄2 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 dimen

sions required, and which is represented in Figure 273, removed from the lines used in constructing it.

The engravings from and including Figure 274 illustrate the lines embracing cut-off cams of varying

limits of cut-off, but all of like travel and dimensions, which are the same as those given for the full stroke cam in Figure 272.

In drawing cut-off cams, the stroke of the engine. plays a part in determining their conformation, and in the examples shown this is assumed to be 4 feet. Figure 274 illustrates the manner of finding essential points in drawing or marking out cut-off cams. With X as a centre, and a radius of 2 feet, draw the circle E 1, showing the path of the crank-pin in making a

revolution. This circle has a diameter of 4 feet, equal

Draw the horizontal centre of circle E 1.

to the stroke of the engine. line B, passing through the Within the limits of circle E 1, subdivide line B into eight equal parts, as at 1, 2, 3, 4, etc. Draw the vertical lines, 1, 2, 3, 4, etc., until they each intersect the circle E 1.

With X as a centre, draw the circle E, having a

242

diameter of 18 inches, equal to the space in the yoke embracing the cam.

From the centre X draw the series of radial lines through the points of intersection of the vertical lines 1, 2, 3, 4, etc., from the circle E 1, and terminating at

18

*--*8-

Fig. 276.

X. We will now proceed to utilize the scale afforded by Figure 274, in laying off the cut-off cam shown in Figure 276, of half stroke limit.

With X as a centre, draw the circle E, Figure 275, having a diameter of 18 inches. Bisect this circle with the straight lines A and B, which bear the same