Movement No. 155 converts reciprocating rectilinear motion into intermittent circular motion using a pawl mounted on an elbow-lever (bell-crank), engaging a toothed wheel. As the elbow-lever is pushed and pulled by a reciprocating rod, it oscillates about its fixed pivot. A pawl attached to one arm of the elbow-lever engages the teeth of a ratchet wheel: on one stroke, the pawl catches a tooth and advances the wheel by one step; on the return stroke, the pawl slides over the teeth without engaging, leaving the wheel stationary. The direction of the wheel’s intermittent rotation can be reversed simply by switching the pawl to the opposite side of the lever — allowing it to engage the teeth in the other direction. This reversible step-feed mechanism was widely used in planing machines, slotting machines, and other metal-cutting tools to incrementally advance the workpiece or table by a precise amount with each cutting stroke of the machine.
155. Reciprocating rectilinear motion into intermittent circular motion by means of the pawl attached to the elbow-lever, and operating in the toothed wheel. Motion is given to the wheel in either direction according to the side on which the pawl works. This is used in giving the feed-motion to planing machines and other tools.