Scroll machining method and machining unit

A machining unit comprising:

• a first driving portion turning a rotary table to which a workpiece is attached;
• a second driving portion moving a tool attached to a spindle relative to the rotary table;
• a control portion controlling the first driving portion and the second driving portion, so that when in a first scroll machining one of an outside wall surface and an inside wall surface of a wall part configured in a scroll shape is machined, the tool is moved relative to the workpiece from an outside of the workpiece toward a center part along a predetermined path while the rotary table turns in a first direction and so that when in a second scroll machining the other of the outside wall surface and the inside wall surface of the wall part is machined, the tool is moved relative to the workpiece from the center part of the workpiece toward the outside by returning along the predetermined path while the rotary table turns in a second direction opposite to the first direction;
• and
• a measurement portion measuring a thickness of the wall part after the first scroll machining and the second scroll machining are finished;
• wherein a tool radius is corrected by an amount of a deviation between a measured value measured by the measurement portion and a design value of the thickness of the wall part, for a subsequent first scroll machining and a subsequent second scroll machining.