the head 46 is withdrawn from contact with the cam by the constant backward force imparted by spring 44 and assumes a spaced relation with the lower cam 16 the continued rotation of the rotary shaft 10 causes the upper cam 14 to contact the fixed follower pin 14 along ramp 14b on the track face of the upper cam 14 and to force the swivel lever 28 to pivot backwardly to its initial position prior to actuation of the driving mechanism the fixed follower pin 30 is forced out of contact with the upper cam 14 by the inclined surface 14c and flat 14d of the track contained on the face of the upper cam 14 the fixed follower pin 30 thereafter is located in the space between the upper cam 14 and the lower cam 16 if spring 44 fails to fully withdraw the movable follower pin 34 from contact with the track of lower cam 16 the wedge shaped surface 16d contained in the face of lower cam 16 will engage the head 46 and will axially drive it away from contact with the lower cam 16 as the lower cam 16 rotates it will be observed that if initiation of the operating cycle for the driving mechanism is commenced at any time other than when the head 46 of the movable follower pin 34 can be driven.