Patent ID: 7891444
Filing Date: 2011-02-22
Classification: B23B,Y10T

Abstract:
1. A drill bit comprising: a plurality of cutting blades arranged in a circumferential direction thereof, the cutting blades being each structured to have a cutting edge formed by a connecting ridge line between a cutting face and a flank thereof; and a tip end portion formed by coupling radially inner ends of the cutting edges to each other at a center portion of a bit tip end when viewed from bottom, wherein at least one of the cutting blades has a first flank at an outer circumference end portion thereof and a second flank at an inner circumference side portion thereof, wherein the first flank has a blade tip side flank close to the cutting edge and a base end side flank formed on a base end side of the blade tip side flank, wherein a tilt angle of the blade tip side flank which is tilted toward an axial direction is smaller than a tilt angle of the base end side flank which is tilted toward the axial direction, and wherein a tilt angle of the second flank which is tilted toward the axial direction is larger than each of the tilt angle of the blade tip side flank which is tilted toward the axial direction and the tilt angle of the base end side flank which is tilted toward the axial direction.