| 摘要 |
A drill (10) in which a cutting edge (12) comprises a concave curved cutting edge portion (12b) on the inner peripheral side and a convex curved cutting edge portion (12a) on the outer peripheral side, wherein, in cross-section orthogonal to the axial center (C), a first convex curve (CL1) corresponding to the convex curved cutting edge portion (12a) and a first concave curve (CL2) corresponding to the concave curved cutting edge portion (12b) intersect each other, so that chips generated from the cutting edge (12) have a uniform, curled shape having no needle-like protrusions and accordingly a relatively short total length, and the discharging of the chips is smoother and the discharge performance is improved. Furthermore, a perpendicular relief angle (beta) having an angular range of 9° to 20° is formed on a second flank (tip flank) (32) continuous from the cutting edge (12) at the tip surface (11), and a chamfer (42) having a chamfer width (CW) in the range of 0.002D to 0.02D is formed on the cutting edge (12). Therefore, wear of the flank and chipping of the cutting edge (12) are minimized, cutting resistance is reduced, and breakage of the drill (10) is minimized. |
