Abstract: An incremental drive mechanism for a switch operating timing cam is disclosed. The mechanism includes a camshaft having a radially extending cam and a cooperating slide which is adapted to reciprocate along a rectilinear path. The slide has first and second cam surfaces which are engaged during a major portion of a single revolution of the camshaft to reciprocate the slide in a positive manner. The slide has a cantilever spring arm which carries a pawl tooth at its end to engage successive teeth provided on the periphery of a switch operating cam drum or disc. A cantilever leaf spring is provided which bears against the slide to urge the pawl tooth into engagement with the cam disc or drum in the event the cantilever spring arm becomes permanently displaced toward the slide.