摘要 |
A drill including: a chip discharge flute; and a cutting edge, the cutting edge being made up of a concavely-curved cutting edge portion formed on an inner circumferential side and a convexly-curved cutting edge portion formed on an outer circumferential side, the drill further including a cross section orthogonal to an axial center having a first convex curve corresponding to the convexly-curved cutting edge portion and a first concave curve corresponding to the concavely-curved cutting edge portion intersecting with each other, a flank following the cutting edge on the tip surface having an orthogonal clearance angle β formed within an angular range of 9 to 20 degrees, and a ridgeline of the cutting edge having a chamfer formed with a width CW within a range of 0.002D to 0.02D (where D is a drill diameter). |