Worm Gear Performance

Abstract

The paper represents an attempt to establish a basis upon which the load-carrying capacity and efficiency of worm gears may be predicted. It forms a supplement to a forthcoming British Standard Specification. The requirements of a worm thread profile are briefly considered and the use of the involute helicoid as a basis of worm thread design is recommended. The geometrical properties of the involute helicoid are discussed and a simple method of determining the zone and lines of contact is given. On a theorem on the curvature of tooth profiles as basis, the relative curvature of worm threads and wheel teeth is determined. A method of comparing the stress conditions between lubricated surfaces making moving line-contact is presented and its application to the determination of the allowable loading on worm gear teeth results in simple formulæ. A comparative method of determining wheel tooth strength is also given. An experimental apparatus has been developed for investigating the friction between surfaces in lubricated line-contact, and some of the results obtained therefrom are described. The relation between the results obtained from rolling and sliding disks and from actual worm gears is discussed, and average values of the coefficient of friction which may be used in design are given.