DRILL

To prevent occurrence of welding to prevent a shoulder part of a cutting blade from being damaged, while securing strength of the cutting blade in the shoulder part of the cutting blade at an outer periphery of the cutting blade and to suppress burr from occurring when the cutting blade gets out of a through-hole.SOLUTION: Chip discharge grooves 7 are formed at an outer periphery part of a tip of a drill main body 1 that is rotated in a drill rotation direction T around a shaft line O. Cutting blades 5 are formed at crossing ridge-line parts between wall surfaces pointing in the drill rotation direction T of the chip discharge grooves 7 and flank faces 6 of the tip. The cutting blade 5 is provided with a main cutting blade part 5B extending from an inner periphery side of the drill main body 1 toward an outer periphery side thereof and a cutting blade-shoulder part 5C extending from an outer peripheral end P of the main cutting blade part 5B to the outer periphery of the drill main body 1 and is subjected to honing. With respect to the outer peripheral end P of the main cutting blade part 5B, a true rake angle is made larger at a negative angle-side and a honing angle is made smaller in an outer peripheral end Q of the cutting blade-shoulder part 5C, in comparison with the outer peripheral end P of the main cutting blade part 5B.SELECTED DRAWING: Figure 2 【課題】切刃外周の切刃肩部における切刃強度を確保しつつ、溶着の発生を防止して切刃肩部の欠損を防ぐとともに、貫通穴の抜け際のバリを抑える。【解決手段】軸線Ｏ回りにドリル回転方向Ｔに回転されるドリル本体１の先端外周部に切屑排出溝７が形成され、切屑排出溝７のドリル回転方向Ｔを向く壁面と先端逃げ面６との交差稜線部に切刃５が形成され、切刃５には、ドリル本体１の内周側から外周側に向けて延びる主切刃部５Ｂと、主切刃部５Ｂの外周端Ｐからドリル本体１の外周に達する切刃肩部５Ｃとが備えられるとともに、ホーニングが施されており、主切刃部５Ｂの外周端Ｐに対して、切刃肩部５Ｃの外周端Ｑにおいては、真のすくい角が負角側に大きくされているとともに、ホーニングの大きさは小さくされる。【選択図】図２