Method for manufacturing a worm shaft

In a worm gear apparatus that includes a housing:

• a worm wheel rotatably supported in and by the housing, and a worm shaft rotatably supported in and by the housing and engaged with the worm wheel, to transmit a rotational force of the worm shaft to the worm wheel, the worm shaft having a worm portion to be engaged with the worm wheel, a small diameter shaft portion formed at a forward end rotatably supported by the housing, and a large diameter shaft portion at the opposite side of the worm portion, a method of manufacturing the worm shaft comprising:
• a step of preparing a rod material having a worm forming portion;
• a step of forming the small diameter shaft portion at least at one axial end of the worm forming portion, wherein a diameter of the small diameter shaft portion is smaller than a diameter of a bottom of a worm tooth to be formed at the worm forming portion;
• and
• a step of forming the worm portion at the worm forming portion by a rolling process with rolling dies, wherein the worm forming portion is rotated and moved in a direction away from the rolling dies during the rolling process, and a surplus material portion of the worm forming portion is extended in a direction opposite to the moving direction of the worm forming portion, so that the surplus material portion flows toward the small diameter shaft portion.