Drill and method of manufacturing drill

A drill having:

• a cutting edge including a surface on which ridgelines are provided;
• and
• at least three different point angles defined by three pairs of ridgelines,
• wherein the three pairs of ridgelines consist of ridgelines that have ends on a common parabola.

A drill having:

• a cutting edge including a surface on which ridgelines are provided;
• and
• at least four different point angles defined by four pairs of ridgelines,
• wherein the four pairs of ridgelines consist of ridgelines that are tangent to a common parabola.

A method of manufacturing a drill,

• the drill comprising a shank and a cutting edge, the cutting edge including a fixed end coupled to the shank, a free end opposite to the fixed end, and a surface on which ridgelines are provided,
• the method comprising:
• setting a material of the drill;
• and
• forming said cutting edge using the material,
• wherein a projected shape of a passing area of the ridgelines of said cutting edge, when said cutting edge is rotated around a tool axis, becomes a line-symmetric and discontinuous line along a parabola, two parabolas, an ellipse, or two ellipses,
• wherein the projected shape is drawn on a projection plane parallel to the tool axis,
• wherein the line-symmetric and discontinuous line comprises a first symmetrical half on a first side of the tool axis and a second symmetrical half on a second side of the tool axis, each of the first and second symmetrical halves comprising at least three discontinuous points that discontinuously connect continuous line portions, the continuous line portions being linear line segments or continuous curves, and
• wherein the at least three discontinuous points of at least one of the first and second symmetrical halves of the line-symmetric and discontinuous line each reside along a common parabola or ellipse that extends convexly from the fixed end of the cutting edge to a vertex located nearer the free end of the cutting edge.

A drill having at least one cutting edge,

• wherein a projected shape of a passing area of a ridgeline of said at least one cutting edge, when said at least one cutting edge is rotated around a tool axis, becomes a line-symmetric and discontinuous line along two parabolas or two ellipses,
• wherein the projected shape is drawn on a projection plane parallel to the tool axis,
• wherein the line-symmetric and discontinuous line comprises a first symmetrical half on a first side of the tool axis and a second symmetrical half on a second side of the tool axis,
• wherein at least three points along the first symmetrical half of the line-symmetric and discontinuous line reside along a first common parabola or ellipse,
• wherein at least three points along the second symmetrical half of the line-symmetric and discontinuous line reside along a second common parabola or ellipse, and
• wherein the tool axis does not coincide with a major axis of either the first common parabola or ellipse or the second common parabola or ellipse.