roll 32a is still being accumulated on the spindle at station a until the transfer roll 42b contacts the empty spindle with a predetermined amount of force sufficient to activate the cutoff knife 44 the amount of force necessary to activate the cutoff knife may be determined for instance by a sensor such as a spring loaded cylinder 50 having a valve arrangement at either end which allows a compressed fluid such as air to pass to a portion of the cutoff knife causing the latter to rotate about its axis z the valve arrangement includes air valves 52a and 52b mounted on the pivots for respectively rolls 32a and 32b and incorporating projecting detents adapted to press against the respective empty spindle in the illustration shown in fig3 the knife blade 42 which is preferably a thin piece of steel with many sharp points is rotated counterclockwise upon activation of the sensor mechanism thereby cutting through the moving sheet and separating it from the sheet which is being wound at station a at the same time the film transfer roll 42b which may be covered with soft rubber presses the sheet against the winding spindle at station b in the case of producing polyethylene plastic sheet the outside of the winding spindle is preferably covered by a strip of sticky or adhesive tape which is adherent on both sides thus after the cut through the sheet is completed a small portion of the sheet between the cutoff point and the nip formed by the transfer roll 42b and the empty spindle is free so as to be adapted for take.