Abstract: High production rates and decreased wear and tear and stress on parts are obtained in a bag fabrication machine with the web fed intermittently by respective bag lengths, for operations such as perforating, transverse severing or welding with the web halted.A sector plate is oscillated between two extreme positions faster in one direction than in the other by a flywheel-carried crank pin orbiting about an axis eccentric from the plate axis; the pin engaging a block sliding in the plate radially of its axis. The plate motion is applied as input to an electrically operated clutch and brake unit and the output is applied to web advance rolls. Switches on the slide block, actuated at the extreme sector positions, control the alternating clutch and brake engagement to drive the rolls for web feed during the slower sector motion of relatively longer duration; and also declutching with braking to halt the web precisely, for and during a faster sector plate return motion.