Manufacturing method for worm wheel, and worm gear reducer

A manufacturing method for a worm gear reducer including a worm wheel (5a) and an operational worm (3), wherein the worm wheel (5a) is meshed with said operational worm (3) at usage, comprising the steps of:

• preparing an operational worm (3) comprising teeth;
• preparing a worm wheel (5a), in which at least a surface layer of a tooth portion (8a) is made of synthetic resin;
• preparing a machining worm (13), in which pitch of teeth of the machining worm (13) in an axial direction thereof is the same as that of said operational worm (3), and providing abrasive grains (14) on a surface of the machining worm (13) by means of electro-deposition;
• disposing the machining worm (13) in a twisting position relative to the worm wheel (5a);
• and
• rotating the machining worm (13) and the worm wheel (5a) with meshing each other so as to machining the tooth portion of the worm wheel (5a),
• wherein said operational worm (3) and machining worm (13) are prepared such that the diameter of the tip and root portions of the machining worm (D13a, d13a) are larger than the diameters of the tip and root portions of the operational worm (D3, d3) by 1 to 10%.