The hob differs from the worm principally in that the outside diameter of the hob is larger to allow for resharpening and to provide bottom clearance in the wormgear. Hobs: The hob for producing the gear is a duplicate of the mating worm with regard to tooth profile, number of threads, and lead. It does not cover helical gears used as wormgears. It covers cylindrical worms with helical threads, and wormgears hobbed for fully conjugate tooth surfaces. This standard is intended as a design procedure for fine-pitch worms and wormgears having axes at right angles. American Standard Design for Fine-pitch Worm Gearing (ANSI B6.9-1977)
Tooth strength except at the coarser end of the fine-pitch range is seldom an important factor durability and accuracy, as they affect the transmission of uniform angular motion, are of greater importance.Ģ) Housing constructions and lubricating methods are, in general, quite different for finepitch worm gearing.ģ) Because fine-pitch worms and wormgears are so small, profile deviations and tooth bearings cannot be measured with the same accuracy as can those of coarse pitches.Ĥ) Equipment generally available for cutting fine-pitch wormgears has restrictions which limit the diameter, the lead range, the degree of accuracy attainable, and the kind of tooth bearing obtainable.ĥ) Special consideration must be given to top lands in fine-pitch hardened worms and wormgear-cutting tools.Ħ) Interchangeability and high production are important factors in fine-pitch worm gearing individual matching of the worm to the gear, as often practiced with coarse-pitch precision worms, is impractical in the case of fine-pitch worm drives. Fine-pitch worm gearing is segregated from coarse-pitch worm gearing for the following reasons:ġ) Fine-pitch worms and wormgears are used largely to transmit motion rather than power. Worm gearing may be divided into two general classes, fine-pitch worm gearing, and coarse-pitch worm gearing. This article will provide a review of common worm gearing types, classes, standards, materials, and methods of fabrication. Worm gearing is found in many different applications for mechanical power transmission, from the tuning pegs of stringed musical instruments to elevators, conveyor systems, and vehicle differential drive systems.