A crankshaft machining system includes a center hole boring device, a post-centering balance meter and a cutting device. The post-centering balance meter is configured to measure the shape of a post-centering crankshaft blank on the basis of a pair of center holes. Additionally, the post-centering balance meter is configured to set a principal axis of inertia on the basis of the shape of the post-centering crankshaft blank and generate center hole positional information for correction that indicates intersections between the principal axis of inertia and both end surfaces of the post-centering crankshaft blank. The center hole boring device is configured to bore a pair of center holes on both end surfaces of another crankshaft blank to be loaded next on the basis of the center hole positional information for correction.

In the process of cutting the outer circumference 10o of a hollow rotating shaft 10 by using a finishing turning tool 36, the position of the finishing turning tool 36 is adjusted in the direction orthogonal to the virtual reference shaft center VS so that the center position CPo of the outer circumference 10o of the hollow rotating shaft 10 is deviated from the virtual reference shaft center VS in the same direction as the direction of the deviation vector Di by an amount corresponding to the magnitude |Di| of the deviation vector Di. This can reduce the unbalance to zero also in the middle of the shaft and sufficiently reduce runout of the hollow rotating shaft 10 even if the rotation speed of the hollow rotating shaft 10 increases. Accordingly, it is possible to further improve the reliability of the hollow rotating shaft 10 at high rotation speed.

In the process of cutting the outer circumference 10o of a hollow rotating shaft 10 by using a finishing turning tool 36, the position of the finishing turning tool 36 is adjusted in the direction orthogonal to the virtual reference shaft center VS so that the center position CPo of the outer circumference 10o of the hollow rotating shaft 10 is deviated from the virtual reference shaft center VS in the same direction as the direction of the deviation vector Di by an amount corresponding to the magnitude |Di| of the deviation vector Di. This can reduce the unbalance to zero also in the middle of the shaft and sufficiently reduce runout of the hollow rotating shaft 10 even if the rotation speed of the hollow rotating shaft 10 increases. Accordingly, it is possible to further improve the reliability of the hollow rotating shaft 10 at high rotation speed.

A machine tool includes a workpiece holding unit to hold a workpiece. A tool holding unit holds a tool. At least one of the workpiece holding unit and the tool holding unit is drivingly rotatable or drivingly movable in a predetermined direction to machine the workpiece with the tool. Temperature sensors are attached to members constituting the machine tool. An estimator calculates an environmental temperature system thermal displacement amount due to a heat source outside the machine tool. A correction magnification processor calculates an environmental temperature system thermal displacement correction amount. Another estimator calculates a driving system thermal displacement amount due to a heat source in the machine tool. A thermal displacement correction amount adder obtains and outputs a total thermal displacement correction amount based on which the machine tool performs thermal displacement correction control.

In the process of cutting the outer circumference 10o of a hollow rotating shaft 10 by using a finishing turning tool 36, the position of the finishing turning tool 36 is adjusted in the direction orthogonal to the virtual reference shaft center VS so that the center position CPo of the outer circumference 10o of the hollow rotating shaft 10 is deviated from the virtual reference shaft center VS in the same direction as the direction of the deviation vector Di by an amount corresponding to the magnitude |Di| of the deviation vector Di. This can reduce the unbalance to zero also in the middle of the shaft and sufficiently reduce runout of the hollow rotating shaft 10 even if the rotation speed of the hollow rotating shaft 10 increases. Accordingly, it is possible to further improve the reliability of the hollow rotating shaft 10 at high rotation speed.

In the process of cutting the outer circumference 10o of a hollow rotating shaft 10 by using a finishing turning tool 36, the position of the finishing turning tool 36 is adjusted in the direction orthogonal to the virtual reference shaft center VS so that the center position CPo of the outer circumference 10o of the hollow rotating shaft 10 is deviated from the virtual reference shaft center VS in the same direction as the direction of the deviation vector Di by an amount corresponding to the magnitude |Di| of the deviation vector Di. This can reduce the unbalance to zero also in the middle of the shaft and sufficiently reduce runout of the hollow rotating shaft 10 even if the rotation speed of the hollow rotating shaft 10 increases. Accordingly, it is possible to further improve the reliability of the hollow rotating shaft 10 at high rotation speed.