Patent ID: 8382404

Claim:
A drill in which a flute for removing a chip is formed from a point to a base end side of a body of the drill, on a side face of the body of the drill to be rotated about an axis, a cutting edge is formed at a ridge portion between a wall surface of the flute which faces a drill rotational direction side and a flank at the point of the body of the drill, and a thinned portion is provided to a web portion of the point of the body of the drill, wherein: the cutting edge is formed in a convex arc shape with a curvature radius being greater than or equal to 0.25 and less than or equal to 1 times a drill diameter; a radial rake angle at an outer peripheral portion of the cutting edge is greater than or equal to −60 degrees and less than or equal to −15 degrees; a corner portion, which is closer to the center of the point of the drill, 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; the drill includes three flutes and three cutting edges; and a center cutting edge having a linear shape is formed at a portion between the cutting edge and the corner portion of the thinned portion that is on the drill rotational direction side with respect to the cutting edge.