8. IN A WET BOARD MACHINE FOR ACCUMULATING PLIES OF MATERIAL, SAID MACHINE OF THE TYPE HAVING A HOLLOW DRUM WITH A LONGITUDINAL SLOT THEREIN, DRUM HEADS HAVING HAND HOLES THEREIN, JOUNRANS UPON WHICH SAID DRUM IS MOUNTED, MEANS FOR REVOLVINGH SAID JOURNALED DRUM, A KNIFE BLADE POSITIONED IN ALIGNMENT WITHIN SAID SLOT AND ACTUATING MEANS ENGAGING SAID KNIFE TO DRIBE AND RETRACT IT THROUGH SAID SLOT, SAID ACTUATING MEANS INCLUDING AT LEAST THREE SPACED APART ACTUATING CYLINDERS, THE IMPROVEMENT THEREIN COMPRISING; A GUIDE RAIL LONGITUDINALLY POSITIONED WITHIN SAID HOLLOW DRUM AND FIXED TO THE INNER SURFACE THEREOF; A PLANAR MOUNTING BEAM POSITIONED CO-EXTENSIVE WITH AND REMOVABLY SECURED TO SAID GUIDE RAIL BY FASTENERS INSERTED ADJACENT SAID HAND HOLES; RETAINING MEANS SLIDABLY CLASPING SAID BEAM TO SAID RAIL TO FACILITATE LONGITUDINAL MOVEMENT THEREBETWEEN; SAID KNIFE ACTUATING MEANS AFFIXED TO SAID PLANAR MOUNTING SURFACE AND REMOVABLY SECURED TO SAID KNIFE BLADE BY FASTENERS LOCATED ADJACENT SAID HAND HOLES WHEREBY SAID KNIFE ACTUATING MEANS AND PLANAR MOUNTING SURFACE ARE SLIDABLE AS A UNIT ALONG SAID GUIDE RAIL FOR WITHDRAWAL FROM ONE END OF SAID HOLLOW DRUM UPON THE DISENGAGEMENT OF SAID FASTENERS ACCOMPLISHED THROUGH SAID HAND HOLES.