| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill bit which does not lower a boring capacity and prevents the breakage of the outside diameter end of a blade edge. SOLUTION: The drill bit has a tip part 10 in which at least two cutter bit parts 1 are formed in the peripheral direction, the joining ridge line 4 between a rake face 2 and a flank 3 formed in each cutter bit part 1 is made a cutter bit, and the inner diameter end of each cutter bit is joined at the central part of a bit tip. At least one of the cutter bit parts 1 has a first flank 3A in a peripheral end part and a second flank 3B in a part on its interior side. The first flank 3A has a blade edge side flank 3a close to a cutter bit and a base end side flank 3b formed on the base end side of the blade edge side flank. The inclination angleα1 in the axial direction of the blade edge side flank 3a is made smaller than the inclination angleα2 in the axial direction of the base end side flank 3b. COPYRIGHT: (C)2005,JPO&NCIPI
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