| 摘要 |
An object of the present invention is to provide a drill bit whose drilling performance does not deteriorate and whose radially outer end of a blade tip is never chipped. A drill bit A comprises: a plurality of cutting blades 1 arranged in a circumferential direction, the cutting blades 1 being each structured to have a cutting edge formed by a connecting ridge line 4 between a cutting face 2 and a flank 3; and a tip end portion 10 formed by coupling radially inner ends of the cutting edges to each other at a center portion of a bit tip end, wherein at least one of the cutting blades 1 has a first flank 3A at an outer circumference end portion thereof and a second flank 3B at an inner circumference side portion thereof, wherein the first flank 3A has a blade tip side flank 3a close to the cutting edge and a base end side flank 3b formed on the base end side of the blade tip side flank, and wherein a tilt angle ±1 of the blade tip side flank 3a which is tilted toward an axial direction is smaller than a tilt angle ±2 of the base end side flank 3b which is tilted toward the axial direction. |
