Abstract: An indexing lapping machine includes a drive piston mounted within a pneumatic cylinder which is reciprocated back and forth due to a pneumatic pressure action on the piston. The piston is connected to a rod which has a lapping tool connected thereto. An actuator rod is also fixed to the piston. The actuator rod has a camming member coaxially mounted thereon and frictionally slidable thereagainst. The camming member is interposed between an abutment member and a timer reset switch such that upon a downward stroke of the piston, the camming member abuts the abutment member and allows the actuator rod to slide the full extent of the piston stroke but during upward movement of the piston, the camming member rides with the actuator rod until the camming member abuts the reset switch which prevents the full raising of the piston and recycles the piston to the downward stroke.