Drill

A drill comprising:

• a cutting discharge groove extending from the tip towards the rear end of a bit formed in the outer periphery of the bit serving as the tip of a drill body that rotates 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, and
• when the bit is viewed from the tip in the axial direction, the tip flank section located in the region on the opposite side of the cutting edge is in the form of a multilevel surface composed of a plurality of flanks arranged along the peripheral direction juxtaposed about a Y axis perpendicular on the axis to an X axis parallel to the cutting edge through the axis, and
• at least one of the intersecting ridgelines of the plurality of flanks that compose the tip flank section contact a drilled material during drilling of the drilled material.

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 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
• an auxiliary groove section is formed, which together with being continuous on the front side in the direction of drill rotation with the cutting discharge groove and extending from the tip to the rear end of the bit, is also cut upward to the cutting discharge groove starting at an intermediate point.

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
• chisel edges located on roughly mutually opposite sides juxtaposed about the axis are formed in the tip flank, and
• this pair of chisel edges is made to recede at roughly mutually the same change in inclination towards the rear end in the axial direction moving towards the outside in the radial direction.