Drill

A drill rotatable around an axis line, the drill comprising:

• a helical flute surface helically provided around the axis line;
• a flank face contiguous to the helical flute surface;
• and
• a thinning face contiguous to each of the helical flute surface and the flank face, wherein
• a ridgeline between the helical flute surface and the flank face constitutes a main cutting edge,
• a ridgeline between the thinning face and the flank face constitutes a thinning cutting edge contiguous to the main cutting edge,
• as viewed in an axis line direction along the axis line, the thinning cutting edge is close to the axis line with respect to the main cutting edge,
• the thinning cutting edge includes
• a curved thinning cutting edge portion that protrudes forward in a rotation direction, and
• a straight thinning cutting edge portion that is contiguous to the curved thinning cutting edge portion and that is close to the axis line with respect to the curved thinning cutting edge portion as viewed in the axis line direction,
• when a first straight line is defined as a straight line passing through the axis line and an outer peripheral position separated rearward in the rotation direction from an outermost peripheral end of the main cutting edge by a predetermined outer peripheral core height,
• an angle formed by the first straight line and the straight thinning cutting edge portion is 135° or more and 160° or less as viewed in the axis line direction,
• a length of the straight thinning cutting edge portion is 10% or less of a diameter of the drill as viewed in the axis line direction,
• an axial rake angle of the straight thinning cutting edge portion is −10° or more and 0° or less in a cross section that is perpendicular to the straight thinning cutting edge portion as viewed in the axis line direction and intersects the straight thinning cutting edge portion,
• the curved thinning cutting edge portion has a first end portion that is a boundary between the curved thinning cutting edge portion and the straight thinning cutting edge portion, and a second end portion opposite to the first end portion,
• an axial rake angle of the curved thinning cutting edge portion in a cross section perpendicular to the tangent of the curved thinning cutting edge portion as viewed in the axis line direction is larger in a direction further away from the first end portion,
• the axial rake angle of the curved thinning cutting edge portion is 5° or more and 20° or less in a cross section that is perpendicular to the tangent of the curved thinning cutting edge portion at the second end portion as viewed in the axis line direction and includes the second end portion, and
• a curvature radius of the curved thinning cutting edge portion is 15% or more and 35% or less of the diameter of the drill as viewed in the axis line direction.