In Fig. 83 the follower is a roll, as before; but instead of traveling in a straight line, it is made to travel along the arc of a circle, being carried on the end of an arm OC, C' being a fixed point about which the arm oscillates. The length of travel 06 is the same as before, and is likewise divided into six equal parts. This method of carrying the follower roll is, perhaps, the most common of all, and is a very effective plan for giving the follower roll easy movement along its path.
Fig. 83. Diagram of Cam with Roll Follower on Oscillating Arm.
The original radius CO is drawn in this case, as in all the others, through the original center 0 of the follower roll. The radii CX and CB, limiting the arcs of rise, rest, and fall, are likewise drawn in the given relation to the original radius CO, and the arcs subdivided precisely as before.
For the purpose of follower rotation, arcs are now struck through the points 1,2,3,4,5, and 6, these arcs being prolonged until they meet the original radius in the points H, K, J, M, P, and Q. Then the rotation of the points H, J, K, etc., produces the intersections R1 R2, R3, etc.; but it should be noted in this case that the follower roll, instead of getting ahead of the radius, as in Figs. 80 and 82, is lagging behind it at each position. The distances R1L1 R2L2, R3L3, R4L4, R5L5, while being laid off equal to. H1, K2, J3, M4, P5, Q6, etc., as in Figs. 80 and 82, are laid off behind the radius in each position on the arcs of rise and fall. These distances are constantly increasing up to point 6, where the roll remains stationary during the period of rest, and then constantly decrease to zero, until the roll reaches the original position at point 0. From the points just found, arcs are struck as before, the radius being equal to the radius of the follower roll.
The tangent line is drawn as a smooth curve to these arcs, and the arc of rest is struck as before, thus developing the outline of the cam.
The cams should be tested by the tracing-cloth method as before.
The pressure lines are drawn precisely as in Figs. 81 and 82; but it is a little more difficult to rotate these pressure lines back to the points in the path of the follower, and the tracing-cloth method is suggested as best for this purpose. This is done by taking a scrap piece of tracing cloth, fixing a pin through it to the center of the cam, tracing upon it, from the paper below, the pressure lines and the centers of the follower. These centers being rotated back until coincident with the corresponding points of the travel, a second point in each pressure line is pricked through on the paper below. Upon the removal of the tracing cloth, each pressure line can then be quickly drawn through these pricked points and the corresponding centers of the follower, thus enabling the action of the cam to be properly judged.