| 摘要 |
Provided is a drill that achieves a shape of chips curled without a needle-like projection and accordingly shortened in overall length and that more smoothly discharges the chips to further improve a tool life. Since a cross section orthogonal to an axial center C of a drill 10 has a first convex curve CL1 corresponding to a convexly-curved cutting edge portion 12a and a first concave curve CL2 corresponding to a concavely-curved cutting edge portion 12b intersecting with each other at an intersection A, chips generated from a cutting edge 12 are curled and formed into a shape having no needle-like projection and accordingly relatively shortened in overall length and are smoothly discharged with enhanced discharge property and, therefore, the tool life of the drill 10 is further improved. |
