Patent ID: 8905819

Claim:
An internal gear machining method which performs internal gear machining on a to-be-machined internal gear by synchronously rotating the to-be-machined internal gear and a barrel-shaped threaded tool in mesh with each other, the to-be-machined internal gear being rotatable about a workpiece rotation axis, the barrel-shaped threaded tool being rotatable about a tool rotation axis having a predetermined crossed axes angle to the workpiece rotation axis, wherein the crossed axes angle is set based on a threaded tool form, and wherein the threaded tool has such a form that an amount of change in a tool radius and the crossed axes angle satisfy a relationship that the crossed axes angle increases as the amount of change in the tool radius increases, where the amount of change in a tool radius is found from a tool diameter of an axially intermediate portion of the threaded tool and tool diameters of axially opposite end portions of the threaded tool.