| 摘要 |
A drill including flutes formed therein and extending from an axially distal end portion thereof toward an axially proximal end portion thereof, so as to provide cutting edges in the axially distal end portion which is formed of cemented carbide. The cutting edges cooperate with each other to define a point angle of the drill that is not smaller than 125° and is not larger than 135°. Each of the flutes is twisted by a helix angle that is not smaller than 20° and is not larger than 30°. Each of the cutting edges has a radially inner end portion which is formed in a web thinning, such that an axial rake angle of the radially inner end portion of each of the cutting edges is not smaller than -5° and is not larger than +5°.
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