Abstract: Hourglass worm drives have been widely used in various industries. Owing to the complexity of its geometrical and meshing relations, the existing load rating formulas re father empirical in manner. This paper is devoted to developing an analytical method to evaluate the instantaneous and mean Herizian load capacity of hourglass worm drives. Based on contact analysis, the actual length of contact line, and radius of curvature at any instant of meshing are considered. Paper takes the new type of SG-71 grindable hourglass worm gearing as a studying example. The calculated results are well conformed with the rated capacities provided by the manufacturer’s catalogs. This method can be extended to other types of double-enveloping worm gears.

Key words: Lead capacity, Worm, Worm whell