To bore a larger center spindle hole and produce a larger driving force by a method wherein the caliber of a circular saw is made large than a value, which is obtained by dividing the sum of the caliber of the circular saw and the specified multiplication of the plate thickness of the circular saw with a specified number.

A hole for locking a center spindle of a circular saw is formed larger than the value, which is obtained by dividing the sum of the caliber of the circular saw and twenty times the plate thickness of the circular saw with thirty. Here, the hole for the center spindle of the circular saw is one for locking the center spindle of the circular saw. Through a larger center spindle, a larger driving force fully rotates the circular saw. A larger calibered center spindle is used by making the hole for locking the center spindle of the circular saw larger for passing the center spindle having the larger caliber of the circular saw in the hole for locking the center spindle of the circular saw in order to exert a larger driving force. Thus, the full rotation of the circular saw by the larger driving force becomes possible. By making the hole for locking the center spindle of the circular saw larger for that, the center spindle having the larger caliber can be employed.