To establish the operating procedures to mount a polisher on the rotary shaft of a disc grinder through a rubber packing and fasten the polisher by screwing a wheel nut, wherein the fastening of the polisher to ensure the greatest reduction of the vibration at grinding can be performed easily.

A wheel washer 2 and a mounting ring 7 in flange pipe form are set on the end of a rotary shaft 1, and a rubber packing 8 and then a polisher 4 are mounted on the flange part 7a of the mounting ring 7, and a wheel nut 5 is screwed on the end of the rotary shaft 1. The screwing is made until the nut 5 abuts to the ring 7, wherein the condition h<(a+b) should be met, where (h) is the length of the cylindrical portion 7b of the ring 7, (a) is the thickness of the packing 8, and (b) is the thickness of the polisher 4, and the setting should be such that the vibration is reduced to the minimum when the polisher 4 is fastened.