urged by means of the tension spring 45 to bear against a control cam 46 non rotatably mounted to the stator 2 it is circular over the major part of its periphery but in the radial direction it has an opening 47 which will be described hereinafter with reference to fig8 so that the cutting blade 32 is not in the way for loading and unloading the plastic bottle with the neck 4 and the dome 5 in a direction parallel to the longitudinal axis 6 of the passage 7 the device has the opening or recess 47 which allows the control roller 27 to be moved radially somewhat closer to the central longitudinal axis 6 and held there in other words the cutting blade 32 can come out of engagement and also be held there when viewing fig8 it can be envisaged that the control roller 27 is continuously in contact pulled by the spring 45 with the control cam 46 outside periphery from the position i at the end of the opening 47 the control cam 46 extends in the counter clockwise direction on a circular path of an outside diameter as indicated at dk diameter curve to the position ii at which the opening 47 begins upon further rotary movement the blade holder 29 is now so adjusted relative to the control roller 27 that the cutting blade 32 is in engagement with the plastic material to be cut over the entire partly.