Fig. 232.
Fig. 233.
To compare the motions of the respective rollers along the line of motion a a we proceed as in [Fig. 232], in which the two dots m and n are the same distance apart as are the centres of the two rollers b and c when in the positions they occupy in [Fig. 228]; hence a pair of compasses set to the radius from the axis of the cam to that of roller b will, if rested at n, strike the arc marked 1 above the line of motion a a, while a pair of compasses set to the radius from the axis of the cam to that of roller c in [Fig. 228] will, if rested at m in [Fig. 232], mark the arc 1 below the line of motion a a. Continuing this process, we set the compasses to the radius from the axis of the cam to that of roller b in [Fig. 229], and mark this radius at arc 2 above the line a a in [Fig. 232]; hence the distance apart of these two arcs is the amount the roller travelled along the line a a while the cam moved from its position in [Fig. 228] to its position in [Fig. 229]. Next we set the compasses from the axis of the cam to that of the large roller in [Fig. 230], and then mark arc 3 above the line in [Fig. 232], and repeat the process for [Fig. 233], thus using the centre n for all the positions of the large roller and marking its motion above the line a a. To get the motion of the small roller c, we set the compasses to the radius from the axis of the cam to the small roller in [Fig. 228], and then resting one point of these compasses on centre m in [Fig. 232], we mark arc 1 below the line a a. Turning to [Fig. 229] we set the compasses from the cam axis to the centre of roller c, and from centre n in [Fig. 232] mark arc 2 below line a. From [Figs. 230] and [231] proceed in the same way to get lines 3 and 4 below line a in [Fig. 232], and we may at once compare the two motions. Thus we find that while the cam moved from the position in [Fig. 228] to that in [Fig. 229], the large roller moved twice as far as the small one, while at [230] the motions were rapidly equalizing again, the equalization being completed at [231].
Fig. 234.
