| 摘要 |
PROBLEM TO BE SOLVED: To reduce thrust and to increase biting performance and centering performance by sufficiently reducing a chisel edge while maintaining the strength of the edge of a tip center part in a metal working twist drill. SOLUTION: The groove bottom 6c of each thinning part 6 formed so as to correspond to each cutting edge 3 is formed of a concave surface. The thinning parts 6, 6 are put into the flank 5 side of the opposite side cutting edge beyond a drill center O, and overlapped with each other by a predetermined amount Y in the direction where the thinning part cutting edge 3a extends as viewed from the front of the drill. An auxiliary thinning part 7 for reducing the width of the chisel edge 8 is formed at the portion of each of the thinning parts 6, 6 positioned at the tip of the drill. COPYRIGHT: (C)2009,JPO&INPIT
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