Threading tool and method of threading

A threading tool comprising:

• a tool main body;
• and
• a cutting edge portion, which is provided on a tip portion of the tool main body and has a rake face and a flank face, the cutting edge portion configured to form a thread groove in a rotating work material by cutting into a circumference of the rotating work material, wherein
• the cutting edge portion comprises:
• a primary cutting edge linearly extending in a tooth width direction of the cutting edge portion viewed from a direction facing the rake face;
• two corner edges, one and other of which are provided on one and other of both ends of the primary cutting edge, respectively, and are in a convex curve shape;
• and
• two secondary cutting edges, one and other of which extend from the one and the other of the two corner edges to a rear end side of the cutting edge portion, respectively,
• the two secondary cutting edges are shorter than the primary cutting edge,
• the one of the two secondary edges extends perpendicularly to the primary cutting edge from one of the two corner edges in a longitudinal direction of the tool main body, the one of the two corner edges being between the one of the two secondary edges and the primary cutting edge, when viewed from the direction facing the rake face, and
• the other of the two secondary edges is slanted to a direction intersecting the primary cutting edge in an obtuse angle that includes the cutting edge portion when viewed from the direction facing the rake face, the other of the two secondary edges configured to form the thread groove, the cross section of which is a trapezoid having one oblique side, in the work material.

A method of forming a thread groove in a rotating work material, comprising:

• moving a tool main body relative to a work material in a rotational axis direction of the rotating work material;
• cutting into a circumference of the rotating work material with a cutting edge portion of the tool main body, which is provided on a tip portion of the tool main body and has a rake face and a flank face, the cutting edge portion cutting in incremental steps at least in a radial direction of the rotating work material;
• and
• forming a thread groove with the cutting edge portion, in the circumference of the rotating work material, the cross section of the thread groove in the work material being a trapezoid having one oblique side;
• wherein the trapezoidal cross section of the of the thread groove is formed by a secondary edge of the cutting edge portion, which is slanted with respect to the rotational axis direction of the rotating work material in an obtuse angle that includes the cutting edge portion when viewed from the direction facing the rake face, and
• wherein the tool main body is moved relative to the work material in the rotational axis direction of the work material while the cutting edge portion is cutting into the circumference of the rotating work material.