An input conveyor, output conveyor, and knife assembly with a blade between the input and output conveyors all reciprocate back and forth as a blade moves perpendicular to the conveyors to cut portioned sized of product, such as ground meat. The cut cycle allows the product feed to keep moving in a continuous manner on conveyors. For ground meat, this system can allow production rates of 150 pieces or more per minute per conveyor line and can improve the accuracy of portioning. The blade is actuated by a profiled cam set that pulls the blade down, and then returns it with a spring to an upper position. The knife assembly can accelerate just after cutting to reduce the potential for sticking to the cut product.