The present invention relates to an apparatus and a method for machining a worm shaft of a double enveloping worm gear composed of a double enveloping worm shaft and a worm wheel, and enables X-axis movement of the worm shaft, Y-axis and Z-axis movements of a worm machining cutter, A-axis rotation of the worm shaft, C-axis rotation of the cutter, and B-axis tilting of a saddle on which the cutter is provided, and thus can facilitate worm shaft machining.

A manufacturing method of a gear includes: rotating a rod-shaped workpiece around a first axis; rotating a tool having a cutting edge around a second axis at a twisted position with respect to the first axis. In a plane perpendicular to the first axis, the workpiece is rotated around the first axis and the workpiece and the tool are relatively moved in the direction parallel to the first axis at the speed synchronized with the rotation speed of the workpiece such that a contour line of the cutting edge of the tool is in rolling contact with a target contour line, which is a contour line of the spiral tooth groove to be formed, at a predetermined point of the target contour line or an extension line of the target contour line without slipping, and rotates while sliding with respect to the target contour line.

A manufacturing method of a gear includes: rotating a rod-shaped workpiece around a first axis; rotating a tool having a cutting edge around a second axis at a twisted position with respect to the first axis. In a plane perpendicular to the first axis, the workpiece is rotated around the first axis and the workpiece and the tool are relatively moved in the direction parallel to the first axis at the speed synchronized with the rotation speed of the workpiece such that a contour line of the cutting edge of the tool is in rolling contact with a target contour line, which is a contour line of the spiral tooth groove to be formed, at a predetermined point of the target contour line or an extension line of the target contour line without slipping, and rotates while sliding with respect to the target contour line.