Patent ID: 7169023

Claim:
A method for manufacturing a die for rolling an hourglass worm, the hourglass worm including a curved root surface with a cross-section extending along an axis of the hourglass worm that defines an arc, the method comprising the steps of: rotating a disk-shaped workpiece about an axis of the workpiece, the workpiece including a peripheral surface with a cross-section extending along the axis of the workpiece that defines an arc corresponding to the arc of the root surface of the hourglass worm; rotating a rotary grindstone about an axis of the rotary grindstone; inclining the axis of the rotary grindstone relative to the axis of the workpiece by a lead angle of the hourglass worm; moving the workpiece relative to the rotary grindstone so that the workpiece, when viewed from the rotary grindstone, swings about a reference axis substantially perpendicular to the axis of the workpiece and extends substantially through a center of curvature of the arc defined on the peripheral surface of the workpiece; and forming teeth grooves, for rolling the hourglass worm, on the peripheral surface of the workpiece by rotating and pressing the rotary grindstone against the peripheral surface of the workpiece while moving the workpiece with respect to the rotary grindstone in synchronism with the rotation of the workpiece.