PURPOSE: To dispense with a space holding cylinder and the replacement of a knife at the time of changing a position by pressing a round knife against the end face of the large diameter portion of a knife installing base board by means of a pressing board fitted on the small diameter portion of the base board and fastening same and, then, reducing the inside diameter of a fastening device to install the knife in the desired position of a rotary shaft.

CONSTITUTION: At the time of fastening, a round knife C is coaxially fitted on the round-knife fitting portion 16 of the small-diameter portion 12 of a base board 1 and brought into contact with the end face of the large-diameter portion 13 thereof and, by screwingly installing a pressure board 21 on a threaded portion 17, the ends of pressing pistons 24 are brought into contact with the round knife C positioned between the pressing board 21 and the large diameter portion 13. By rotating a threaded shaft 33, a pressure piston 32 is pushed and moved toward the bottom portion side of a pressure chamber 29. Thereupon, the pistons 24 are pressed to the round knife C side with a force scores times the advancing force of the piston 32 and the ends of the pistons 24 press the round knife C against the end face of the large-diameter portion 13 with uniform forces to perform fastening. Then, the fastening device 1, 21 is slidingly fitted on a rotary shaft S and placed in a defined position and, by rotating threaded shafts 8, a piston 7 is pushed and moved to the bottom portion side of a pressure chamber 4. Thereupon, the inside diameter of the base board 1 is reduced coaxially fastening the round knife C fitted on the rotary shaft S.