Abstract: A system or apparatus of monitoring and adjusting the location of a perforation cut during production of a plastic sheet.

Abstract: A percussion bit assembly includes a percussion bit having an upper, elongated bit shank, a lower bit head, and a bit skirt disposed intermediate the bit shank and the bit head. The percussion bit has an axial bore extending longitudinally through at least the bit shank and the bit skirt and at least one receptacle extending radially outward from the lower portion of the axial bore. A bit retainer includes at least one longitudinal member and at least one lateral member. The longitudinal member extends longitudinally within the axial bore of the percussion bit from an upper end portion, mounted within the upper portion of the axial bore, to a lower end portion disposed in the lower portion of the axial bore. The lateral member extends laterally from a radially inner end portion connected to the lower end portion of the longitudinal member to a radially outer end portion mounted in the receptacle.