Abstract: A turning process method for processing a step-shaped workpiece includes: feeding a tool in a rotation axis direction and/or a radial direction of a workpiece while rotating the workpiece; using a tool that includes an insert with a main cutting edge having a straight portion and a machine tool having a pivot shaft of the tool in the machine side; processing a peripheral surface of the small diameter portion by turning the pivot shaft so as to have a cutting edge angle of less than 90°, the cutting edge angle having an angle between the straight portion of the main cutting edge and the rotation axis direction; and processing an end surface and a peripheral surface of the large diameter portion by turning the pivot shaft so as to have the cutting edge angle of 90° or more at a front of the large diameter portion.

Abstract: A machine tool is configured to machine a workpiece by rotating a tool and/or the workpiece. The machine tool includes a natural frequency changing unit configured to change a natural frequency before machining or during machining in the tool or a supporting portion supporting the tool.

Abstract: A turning method for performing a turning on a workpiece in a machine tool includes: feeding a tool in a rotation axis direction and/or a radial direction of a workpiece while rotating the workpiece, the tool including an insert having a side cutting edge, the side cutting edge including a straight line portion; and feeding the tool in the rotation axis direction and the radial direction and in a predetermined inclined direction that is non-parallel to a final machining surface of the workpiece, so as to perform a turning such that a cutting edge angle as an angle formed by the straight line portion of the side cutting edge and the inclined direction becomes less than 90°.

Abstract: A turning process method for processing a step-shaped workpiece includes: feeding a tool in a rotation axis direction and/or a radial direction of a workpiece while rotating the workpiece; using a tool that includes an insert with a main cutting edge having a straight portion and a machine tool having a pivot shaft of the tool in the machine side; processing a peripheral surface of the small diameter portion by turning the pivot shaft so as to have a cutting edge angle of less than 90°, the cutting edge angle having an angle between the straight portion of the main cutting edge and the rotation axis direction; and processing an end surface and a peripheral surface of the large diameter portion by turning the pivot shaft so as to have the cutting edge angle of 90° or more at a front of the large diameter portion.