Machining method for a threaded section and machining device

A threaded section machining device comprising:

• a rotary drive shaft rotated and driven by a first drive device;
• a grip section for concentrically fastening one end of a rod-shaped or tubular-shaped machined article to the rotary drive shaft so as to be able to integrally rotate with the rotary drive shaft;
• a measurement means for measuring an amount of thermal expansion in an axial direction of the machined article during machining;
• a machine tool for machining the machined article;
• an axial feeding device driven by a second drive device and for causing relative displacement in the axial direction between the machine tool and the machined article;
• and
• a controller for controlling a rotational speed of the rotary drive shaft or a feeding speed of the axial feeding device;
• and
• the threaded section machining device forming a threaded section around an outer-circumferential surface of the machined article by causing the machined article to rotate by rotating the rotary drive shaft, and causing the machine tool to move in the axial direction relative to the machined article;
• and
• the controller obtaining history information for an amount of thermal expansion of the machined article being machined from the measurement results, and setting a speed of relative rotation or speed of relative displacement for a machined article to be machined next based on the correlation between the history information for the amount of thermal expansion of the machined article that has been machined;
• wherein, after at least two machined articles have been machined, the threaded section machining method further comprises a step of finding a correlation between the history information for the amount of thermal expansion of the at least two machined articles that have been machined and the number of machinings;
• and
• the speed of relative rotation or the speed of relative displacement for a machined article to be machined next is set based on the history information for the amount of thermal expansion of the machined article that has been machined and the correlation between the history information for the amount of thermal expansion of the machined articles that have been machined.