| 摘要 |
PROBLEM TO BE SOLVED: To provide a twist drill with superior durability preventing welding and crimping of an outer circumference part in high speed cutting of 25 m or more when perforating a material relatively having ductility such as stainless steel. SOLUTION: In this twist drill made of coated high speed steel, a helix angle is provided as a high helix angle of 35 to 45 deg., a tip cutting edge is formed protrusively as viewed from a tip of the drill, the tip cutting edge is provided 1 to 10% of a cutting part diameter to the rear in a rotating direction with respect to an imaginary line connecting a most projecting part of the protruding part to a thinning edge, a connecting part of the tip cutting edge and an outer circumference is chamfered, and the thinning edge is formed in an X shape. It is composed by using high speed steel, particularly powdered high speed steel, and providing one layer or a plurality of layers of TiA1N film, a hard substance comprising TiN film or the like, or a lubricative coat such as DLC or a chromium compound in a portion of a groove part of a drill main body including at least a cutting edge tip.
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