| 摘要 |
PROBLEM TO BE SOLVED: To maintain high rigidity of a drill body and to have good drilling accuracy. SOLUTION: Only one chip discharge groove 11 is formed around the periphery of a cutter tip part 10. The extreme end projected to the extreme end of an edge flank 12 in the O axis direction is structured at one point and is positioned on the O axis. When the cutter tip part 10 is seen from the O axis end, the edge flank 12 is structured with a multi-stage face that is composed of the second to fourth flanks 14B, 14C and 14D arranged in the peripheral direction and the opposite side first flank 14E that is surrounded by the second to fourth flanks 14B, 14C and 14D and is crossing with the O axis. COPYRIGHT: (C)2004,JPO
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