The present invention provides a looseness-prevention screw thread structure including a screw thread having a predetermined pitch, a no-load flank which is an inclined surface in a direction in which the screw thread is advanced, and a load flank which is an inclined surface in a direction in which the screw thread is retracted, the no-load flank and the load flank being formed at both sides of the screw thread, in which the no-load flank of the screw thread includes: a first tangential portion which abuts against an arc portion formed at a thread crest of an opposing fastening object; and a second tangential portion which has a preset angle with respect to the first tangential portion and abuts against the arc portion.

A cutting insert according to one aspect has a flat plate shape including a first main surface having a polygonal shape, a second main surface located opposite to the first main surface, and an outer peripheral surface located between the first main surface and the second main surface. The cutting insert includes a cutting portion located in regions including at least a corner portion of the first main surface, and a main body portion located in a region other than the corner portion. A thickness of the main body portion is larger than a thickness of the cutting portions, and the main body portion includes a recessed portion or a protruding portion located in the outer peripheral surface thereof.

A die for a pipe threading operation includes a body portion formed of a first material, and a tooth portion coupled to the body portion and formed of a second material that is different than the first material. The tooth portion having a plurality of teeth.

A machine tool includes a spindle capable of holding a workpiece and rotatable on a spindle axis and a tool post on which a tool is attachable to machine the workpiece held by the spindle. The tool post includes a first turnable holder turnable on a first turning axis perpendicular to the spindle axis. The first turnable holder has a first tool unit mounting part where a rotary tool is attachable. The tool post further includes a second turnable holder turnable on a second turning axis perpendicular to the spindle axis and different from the first turning axis. The second turnable holder has a second whirling tool mounting part where a thread whirling tool is attachable.

A cutting insert 2 includes an upper surface 6, a lower surface 7 on a side opposite to the upper surface 6, and a peripheral side surface 8 connecting the upper surface 6 and the lower surface 7. A cutting edge 61 is formed in at least a part of a first ridgeline 60 where the upper surface 6 and the peripheral side surface 8 intersect. At least one bottomed recess 10 recessed from the lower surface 7 to the upper surface 6 is formed in an outer peripheral portion of the lower surface 7. Each of the recesses 10 is formed in a substantially triangular shape having a first vertex P, a second vertex Q, and a third vertex R. The first vertex P and the second vertex Q are respectively positioned on a second ridgeline 70 where the lower surface 7 and the peripheral side surface 8 intersect. The third vertex R is positioned on the lower surface 7 and separated from the second ridgeline 70.

A machining method, for a CNC-lathe for forming a predefined thread in a work piece, includes the steps of: rotating the metal work piece around a rotational axis thereof; moving a threading tool along a longitudinal direction through a set of passes, wherein the longitudinal direction is parallel/coinciding to the rotational axis; oscillating the threading tool in a radial direction during a first pass and first frequency, the threading tool moving between a first radial distance (D1) and a second radial distance (D2), (D1) being greater than (D2); oscillating the threading tool in a radial direction during a second pass and second frequency, the threading tool moving between a third radial distance (D3) and a fourth radial distance (D4), (D3) being greater than (D4) and smaller (D1), and (D4) being smaller than (D2); and during a last pass moving the tool without oscillation in the radial direction.

A threading tool includes: 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 includes: a primary cutting edge extending in a tooth width direction of the cutting edge portion; 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. Two secondary cutting edges are shorter than the primary cutting edge. At least one of the two secondary edges is slanted to a direction intersecting the primary cutting edge in an obtuse angle.

A thread cutting insert for cutting threads includes a plurality of cutting teeth disposed along a cutting portion, each cutting tooth is provided with an allocated chip former, and the chip formers are provided on a rake face of the thread cutting insert. The shape of at least two cutting teeth is different from each other. At least one cutting tooth along the cutting portion is provided with an allocated chip former the shape of which is adapted to the shape of that cutting tooth which, with respect to an order of engagement during cutting operation, precedes the subsequent cutting tooth along the cutting portion such that the at least one chip former has a shape adapted to the cross-section of chips encountered by it. A set of at least two thread cutting inserts, a thread cutting tool and a method for cutting threads, are also provided.

A method for cutting a thread on a rotating workpiece by means of a cutting tool having a cutting edge. The method includes sequentially performing a number of passes, each pass includes simultaneously moving the cutting tool and/or the workpiece relative to each other along and oscillating the cutting tool towards and away from workpiece rotational such that the cutting edge exits and enters the workpiece forming an air cut. The air cuts performed in a final pass are longer than all the other passes.

A threading insert includes a top surface, an opposite bottom surface, a side surface connecting the top surface and the bottom surface, and a first tooth. The first tooth has a first cutting edge, the first cutting edge including a first top cutting edge connecting a first leading cutting edge and a first trailing cutting edge. The first cutting edge has an edge roundness and the size of the edge roundness varies along the first cutting edge.