Fig. 35.
Fig. 37.
Fig. 41.
Fig. 42.
We may now consider the relative positions these two cams will occupy when keyed up on the side shaft. Assuming that we have both cams finished to the proper shape and size, and the keyway cut in the side shaft, we can commence to mark off the position of keyway in the air cam. With the crank in the position shown in fig. 35, the air cam is slipped on to the side shaft and brought to the position shown in fig. 32. The keyway being already cut in the side shaft, the position for that in the cam may be scribed off, as shown by dotted lines (fig. 32), the cam removed, and the keyway cut. It is as well, however, to check this mark by turning the crank round to position shown in fig. 37, i.e., the closing of air valve. The side shaft will also turn through exactly half this angle, so that when the cam is again slipped on the latter, the scriber marks and keyway in shaft should be exactly in line, as they were in fig. 32, and the fall of the cam—the closing portion—should just be touching roller R, but not sufficient to keep the valve open (see fig. 38). The slightest movement of the crank from this point in a forward direction should result in a little play being felt in the lever L, assuming that the cam is also moved just enough to keep the scriber marks in line with the existing keyway.
