| 摘要 |
A cutting edge 18 is provided on the end of a cutter tip 12 on a gun drill body 1. The cutting edge 18 has: a radially inner region providing a convex curved cutting edge portion 23, a radially outer region providing a straight cutting edge portion 19 and an intermediate region which provides a concave cutting edge portion 22 having a tapered portion 20 and a concave portion 21. The convex curved cutting edge portion 23, when viewed in the direction of the axis O, presents an arc shape, the radius R of the curvature of which is determined in relation to the outside diameter D of the gun drill so as to range from 0.1xD to 0.4xD. Thus, a gun drill is provided which exhibits an enhanced severing effect to cut metal chips into pieces so as to prevent clogging, as well as to prevent an increase in the cutting resistance, thus meeting the demand for a greater feed rate. |
