| 摘要 |
PROBLEM TO BE SOLVED: To provide a user-friendly drill bit which puts up with prolonged use by raising the strength of a neighborhood of a blade edge section without affecting the depth of a chip discharge groove of the drill bit. SOLUTION: In the drill bit where a chip discharge groove 4 is ground and formed with twist from a blade edge section which fixes a cutting edge tip 3 to a periphery of a round bar bit body 1, and a beltlike periphery surface 11 is formed between an open end edges of the chip discharge groove 4 which adjoins each other by the periphery of the bit body, a periphery surface width alteration section 11a which decreases periphery surface width gradually from the blade edge section is formed to the blade edge section width. COPYRIGHT: (C)2005,JPO&NCIPI
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