Thread milling cutter and internal pipe thread machining method using the same

A thread milling cutter helically fed, comprising

• a tool body having a cutting blade portion at an axial tip side of the tool body, a shank portion and a rotation axis defining an axial tip side direction and an axial shank portion direction, the cutting blade portion having a plurality of cutting blades separated in a circumferential direction by chip discharge grooves, each cutting blade having a plurality of trimming blades for forming an internal thread in a workpiece, the plurality of trimming blades being separated from each other by a respective concave valley;
• the plurality of trimming blades being formed in an outer circumference of the axial tip side, protruding in an external, radial direction away from the rotation axis;
• wherein in a plan view of a rake surface of each trimming blade, each trimming blade has, sequentially in the axial shank portion direction, an inclined leading cutting edge, a first chamfered cutting edge, a second chamfered cutting edge, a top cutting edge, a third chamfered cutting edge, a fourth chamfered cutting edge, and a declined trailing cutting edge, a non-zero angle being formed between each cutting edge of each trimming blade;
• wherein in the plan view, each chamfered cutting edge has a width respectively smaller than the width of the top cutting edge, and the width of the top cutting edge being smaller than a width of each of the inclined leading cutting edge and the declined trailing cutting edge;
• wherein each trimming blade has, sequentially in the axial shank portion direction, an inclined leading clearance surface intersecting the inclined leading cutting edge, a first chamfered clearance surface intersecting the first chamfered cutting edge, a second chamfered clearance surface intersecting the second chamfered cutting edge, a top clearance surface intersecting the top cutting edge, a third chamfered clearance surface intersecting the third chamfered cutting edge, a fourth chamfered clearance surface intersecting the fourth chamfered cutting edge, and a declined trailing clearance surface intersecting the declined trailing cutting edge, a non-zero angle being formed between each clearance surface of each trimming blade;
• and
• an axial width v, being measured parallel to the rotation axis, of the respective concave valley separating each trimming blade, an axial width u of a respective trimming blade of the plurality of trimming blades, being measured parallel to the rotation axis, between an intersection point of the inclined leading cutting edge and the first chamfered cutting edge and an intersection point of the fourth chamfered cutting edge and the declined trailing cutting edge, the axial width v being larger than the axial width u.