Abstract: In a method of dressing a barrel worm-shaped tool, a disc-shaped disc dresser (13) meshes with a barrel worm-shaped grinding wheel (12) having its diameter gradually increasing from the two end portions in the axial direction thereof towards the middle portion thereof and used to grind an internal gear (11). The barrel worm-shaped grinding wheel (12) rotates around a tool-rotating shaft (B) disposed at a predetermined shaft angle (A1) with a vertical work-rotating shaft (C1) for the internal gear (11). The disc dresser (13) rotates around a dresser-rotating shaft (D), the disc dresser (13) being disposed at an angle equal to a helix angle of the internal gear (11). While the barrel worm-shaped grinding wheel (12) and the disc dresser (13) mesh with each other and are rotating, the barrel worm-shaped grinding wheel (12) and the disc dresser (13) revolve relative to each other within a horizontal plane.

Abstract: A method of dressing a barrel worm-shaped tool to carry out the dressing of a barrel worm-shaped tool formed to grind tooth face of an internal gear with precision, dressing apparatus, and internal-gear grinding machine are provided. For this purpose, a disc-shaped disc dresser (13) is made to mesh with a barrel worm-shaped grinding wheel (12) having its diameter gradually increasing from the two end portions in the axial direction thereof towards the middle portion thereof and used to grind an internal gear (11). The barrel worm-shaped grinding wheel (12) is made to rotate around a tool-rotating shaft (B) disposed at a predetermined shaft angle (A1) with a vertical work-rotating shaft (C1) for the internal gear (11). The disc dresser (13) is made to rotate around a dresser-rotating shaft (D), the disc dresser (13) being disposed at an angle that is equal to a helix angle of the internal gear (11).

Abstract: The improved hourglass worm gear which has been produced by grinding a blank for the worm gear by rotating a grinding wheel about a grinding wheel shaft A while turning the grinding wheel shaft A about a tool shaft A3 which extends in parallel with a wheel shaft A2 perpendicular to a worm shaft A1 is characterized in that a cross-sectional shape of the grinding wheel taken in a plane inclusive of the grinding wheel shaft A exhibits a circular arc.Since the cross-sectional shape of the grinding wheel for successively grinding a series of gear tooth surfaces on the hourglass worm gear is contoured in the form of a circular arc, the hourglass worm gear assures that a radius r of the circular arc has an increased degree of freedom and an ideal contact pattern can be obtained by properly adjusting the radius r.

Abstract: The improved hourglass worm gear which has been produced by grinding a blank for the worm gear by rotating a grinding wheel about a grinding wheel shaft A while turning the grinding wheel shaft A about a tool shaft A3 which extends in parallel with a wheel shaft A2 perpendicular to a worm shaft A1 is characterized in that a cross-sectional shape of the grinding wheel taken in a plane inclusive of the grinding wheel shaft A exhibits a circular arc.Since the cross-sectional shape of the grinding wheel for successively grinding a series of gear tooth surfaces on the hourglass worm gear is contoured in the form of a circular arc, the hourglass worm gear assures that a radius r of the circular arc has an increased degree of freedom and an ideal contact pattern can be obtained by properly adjusting the radius r.