| 摘要 |
PURPOSE:To provide a broach having a long life and a high degree of accuracy by making the heights of the forward ends of at least those of cutting edges which initially perform cutting operation, equal to each other so that the damage of a part of the cutting edges is compensated by the other cutting edges having the equal height. CONSTITUTION:A broach B is made to pierce through a prepared hole in a workpiece so that the pull-out holding section 7 of the broach is allowed to be gripped by a pull-out head so as to hold the rear holding section 6, and when it is pulled in the direction of the arrow 23, the forward guide part 8, the roughly cutting edge part 2, the intermediate finishing cutting part and the rear guide part 7 form a through-key groove in the mentioned order. Since the roughly cutting edge part 14 performs at first cutting, large shocks are effected. However, since the heights of the cutting edges 10,... constituting the cutting edge part 14 are all equal to each other, even though the foremost cutting edge 10 is damaged, the cutting edge having the equal height in the rear of the former succeeds the cutting in the same condition. The heights H of the cutting edges successively vary from the cutting edge part 14 to the cutting edges part 17 which perform roughcutting. Further, the heights of the cutting edges are also successively vary from the cutting edge parts 18 to 22 so that a certain process is carried out.
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