the rotor 28 is generally driven by an electric motor not shown although the rotor 28 is illustrated as having five arms 26 in the preferred embodiment it will be understood that there may be more or less arms it has been found that rotor knives 24 and associated bed knives 22 of the type manufactured and sold by nelmor company inc north uxbridge mass may be employed to satisfactorily achieve certain objectives of the invention it will be noted from an examination of fig2 the rotor knives 24 extend the full length of the knive assembly and are mounted at a slight angle in respect of the longitudinal axis of the rotor shaft 28 such disposition of the rotor knives 24 causes the cutting edges to cooperate with the cutting edges of the bed knives 22 to create or produce a shearing action therebetween this shearing action tends to overcome the beating or hammering of the material being treated the material being treated is truly cut or sheared greatly assisting in the reduction of the amount of dust or fines which might otherwise be produced the reduction in the dust or fines greatly reduces the dust causing housekeeping problems and increases the productivity of equipment the presence of dust and or fines causes considerable problems in the efficient transfer of the material being treated resulting in unnecessary energy consumption and waste the screen 20 is located directly below the knives 22 24 the screen.