| 摘要 |
A drill in which a flute is formed from a point to a base end side of a body of the drill, on a side face to be rotated about an axis, a cutting edge is formed between a wall surface of the flute which faces a drill rotational direction side and a flank at the point of the body, and a thinned portion is provided to a web portion of the point. The cutting edge is formed in a convex arc shape with a curvature radius 0.25 to 1 times a drill diameter; a radial rake angle at an outer peripheral portion of the cutting edge is −60 to −15 degrees; a corner portion, closer to the center of the point, of the thinned portion is formed in an arc shape with a curvature radius of at least 0.1 mm and not greater than 0.05 times the drill diameter; and the drill includes three flutes and three cutting edges.
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