| 摘要 |
PROBLEM TO BE SOLVED: To prevent the occurrence of chipping or the like by securing the tip strength of a cutting edge without carrying out honing to the cutting edge according to a honing process in drilling a fragile material. SOLUTION: A plurality of chip discharge flutes 12 opened to the tip of an approximately cylindrical drill body 11 are formed at the tip part outer periphery of the drill body 11 rotated around an axis O, and a plurality of tip faces 14 intersecting with inclination to the axis O, with the mutual intersecting ridgeline L reaching the outer periphery of the drill body 11 without intersecting the tip side open edges of the chip discharge flutes 12. The intersecting ridgeline L of these tip faces 14 is made a cutting edge 15.
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