| 摘要 |
PURPOSE:To improve a property of being ground without reducing the life of a broach by reducing the heights of the tooth ends of finishing teeth by stages from the finishing teeth on the frontmost row to the finishing teeth on the rearmost row in a finishing teeth zone in order. CONSTITUTION:A finishing teeth zone 7 consists of a first finishing teeth group 8 consisting of two rows of finishing teeth 1, 2 and a second finishing teeth group 9 consisting of finishing teeth 3, 4. Although the tooth ends of the finishing teeth 1, 2 are of equal height while the tooth ends of the finishing teeth 3, 4 are also of equal height, the height of tooth ends of the finishing teeth 1, 2 is made higher than that of the finishing teeth 3, 4. A land A having a 0 deg. of clearance angle phi which is continuous with the rear of a cutting edge and a flank continuous with the rear of the clearance angle are provided on each of the finishing teeth 1-4. Although all the lands A are of equal width, the clearance angle phi is approx. 1 deg. for the finishing teeth 1, 2 and approx. 0 deg.30' for the finishing teeth 3, 4. Accordingly, regrinding because of wear can be repeated until the height of the tooth ends of the first finishing teeth group 8 become equal to that of the second finishing teeth group 9, improving a property of being ground without reducing a life.
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