<p>A cutting mechanism (10) for cutting fibers entrained within a viscous flow is herein disclosed. The present invention is typically part of a system for preparing fiber reinforced molding materials. Entrained fibers are conveyed to the cutting mechanism (10) which cuts the continuous strand of reinforcing fibers into predetermined lengths and conveys the fiber reinforced molding material to an output device. The cutting mechanism (10) itself comprises a housing (14) having a bore (30) with an inlet and an outlet (60) and a bed knife (40) disposed therein. The bed knife (40) has an inlet channel (42) formed therethrough that is aligned with the gullets (56) of a rotating cutter such that the gullets (56) of the rotating cutter are rotated past the inlet channel of the bed knife in substantial alignment therewith. Fibers entrained within the molding material flow into the gullets of the rotating cutter and are cut to a predetermined length and then conveyed to an output device.</p>