A positioning structure for a worm wheel which is configured to mesh with a worm spindle and contains: a body, a plurality of rolling assemblies, and at least one attaching material. The body includes plural accommodating grooves and plural recesses, wherein each recess forms on a bottom face of each accommodating groove and communicating with said each accommodating groove. Each rolling assembly includes a holder, a rolling ball, and a magnetic attracting element, wherein a width of the holder is less than a width of said each accommodating groove so as to form a gap between the holder and said each accommodating groove. Each attaching material is filled in the gap, and said each rolling assembly is adjustably moved to a fixing position of said each accommodating groove by using said each recess, such that said each attaching material locates the holder in said each accommodating groove.

A rotary table (1) includes a base body (10), a worm wheel (21), an inner ring (22), a plurality of rolling elements, and a worm screw unit (30). The worm screw unit (32) includes a worm screw (31) and a worm screw housing (32). The worm screw housing (32) has an opposing surface that faces an outer circumferential surface (21B) of the worm wheel (21). The worm screw housing (32) includes a flange portion (325) that protrudes from the opposing surface and covers a side face (215A) that, of the first gear (215) facing the opposing surface, is on the opposite side from the base body (10) in the axial direction of the worm wheel (21).

A worm drive has a worm and a worm wheel. Meshing assemblies are formed about the worm wheel each comprising a ball and a cup receiving a portion of the ball. Each cup is orientated at an acute angle toward the worm drive relative to a periphery of the wheel. The worm presents a concavely tapering side profile complementing a peripheral portion of the worm wheel. Consequently portions of the balls mesh with the worm and are free to rotate and so reduce shear forces between the worm and the worm wheel in use.

A positioning structure for a worm wheel which is configured to mesh with a worm spindle and contains: a body, a plurality of rolling assemblies, and at least one attaching material. The body includes plural accommodating grooves and plural recesses, wherein each recess forms on a bottom face of each accommodating groove and communicating with said each accommodating groove. Each rolling assembly includes a holder, a rolling ball, and a magnetic attracting element, wherein a width of the holder is less than a width of said each accommodating groove so as to form a gap between the holder and said each accommodating groove. Each attaching material is filled in the gap, and said each rolling assembly is adjustably moved to a fixing position of said each accommodating groove by using said each recess, such that said each attaching material locates the holder in said each accommodating groove.