Abstract: A comminuting apparatus for rubber has two vertically mounted opposing facing grinding stones of large size having hollow centers. Interposed between these two stones, both of which, as stators, are fixed and do not rotate, is a single rotor having double-sided opposed abrasive grinding stone faces, mounted for rotation but floating laterally or horizontally in position between the two opposed fixed stones. The spacing between the opposed sets of grinding stones is set by increasing or decreasing the spacing between the outer most stator and the fixed inner stator. So long as the rotor rotates for grinding, the floating center stones will position themselves equally between the two stators so as to equalize the dynamic slurry pressure imposed during the grinding process upon the faces of the stones.