Patent ID: 7018144

Claim:
A drill comprising: a cutting discharge groove extending from the tip to the rear end of a bit formed in the outer periphery of the bit serving as the tip of a drill body that is rotated around an axis, and a cutting edge formed in the intersecting ridgeline between a wall surface facing towards the front side in the direction of drill rotation of the cutting discharge groove and a tip flank of the bit; wherein, there is only one cutting discharge groove, the leading edge that protrudes farthest towards the tip in the axial direction in the tip flank is composed at a single point, and the distance between this leading edge and the axis is (5/100)D or less with respect to the maximum outer diameter D of the bit, and when the bit is viewed from the tip side in the axial direction, the tip flank is in the form of a multilevel surface composed of a plurality of flanks arranged along the peripheral direction, and a reverse side first flank formed so as to be surrounded by the plurality of flanks arranged along the peripheral direction and intersect with the leading edge.