The follower positions, Fig. 80, are chosen and drawn precisely as in Fig. 79; in this case, however, the path of the follower does not intersect the center of the cam, but, if produced, would pass at some distance to one side of it. This changes materially the development of the cam, as will subsequently be noted.
The diameter of base circle and center of cam being chosen as before, draw the original radius CO. This original radius is the one to which all subsequent radii are related. Treating this radius the same as the original radius CO in Fig. 79, the radius CX is drawn, making the arc of rise 150° as before. The radius CB is then drawn, giving the 30° arc of rest, and leaving the arc of fall between CB and CO 180° as before. Since the cam is to have uniform motion, the subdivisions of the arcs are equal, and are made in exactly the same manner as in Fig. 79.
The follower is now rotated about the cam by the compasses, in similar manner to that in Fig. 79, producing the intersections R1 R2, R3, R4, etc. Now, however, the introduction of a new step should be noted. The original radius CO, not being coincident with the path of the follower OT, the intersections R1 R2, R3, etc., do not represent the actual positions of the point of the follower when rotated. During the arc of rise, the follower is gaining on the radius, and the increasing distances R1L1, R2L2, R3L3, etc., must be set off ahead of the radii, equal to the distances II1, K2, J3, etc. In similar fashion, during the arc of fall, the decreasing distances F6 N6, F5 N5, F4 N4, F3, N3, must be set off ahead of the radii, equal to Q6, P5, M4, J3, etc.
Fig. 80. Diagram of Cam with Pointed Follower Off Center.
A smooth curve is now drawn, not through the original points of intersection with the cam radii, as in Fig. 79, but through the points set off as above from these intersections. In other words, the cam curve is drawn through points L1, L2, L3, L4, etc., and N6, N5, N4, N3, etc.
A piece of tracing cloth should be laid over the cam, the outline traced upon it, the radii marked, and then the tracing cloth rotated about the pin point, as in Fig. 79, to see if the cam in its successive positions just touches the follower in each of its positions.
The pressure line at each position of the follower is, as in Fig. 79, normal at the point of contact.