Subsequent to a brief review of the development of the worm-gear drive for motor-trucks and the gear-ratios considered most desirable, the author discusses comparatively the worm-gear and the spiral-bevel gear with regard to their application for specific service, as well as with regard to their cost and length of life.
It is brought out that the worm-gear is, after all, very similar in action to any sliding, or journal, bearing. A certain amount of involute rolling-action takes place in the action of the gearing, the magnitude of which increases with the gear-ratio; but the primary action is one of sliding of the worm-threads across the gear-teeth. Simple as this fact is, the prejudice fostered by many people against worm-gears can be traced to lack of appreciation of it. Due to the nature of the surfaces in contact, the best obtainable bearing takes the form of a narrow strip running across the gear-tooth, and the bearing pressures obtained are high. Therefore, it is indicated clearly that the most favorable bearing-conditions should be maintained.
Lubrication of worm-gearing is considered, as well as the kinds of bronze and steel most suitable as worm-gear material. As to the mechanical strength of worm-gears, the difficulties of estimating this correctly are cited and it is explained that wide variations in the quality of lubricant used, in kinds of material, in design and in workmanship are responsible.
In conclusion, it is said that the limit of load on worm-gearing seems to be set by the fatigue limits of the bronze. Therefore, the author looks to nickel-bronze, with its greater ductility and length of fatigue life, to increase the load-carrying capacity of worm-gearing and says that experiments to prove or disprove this possibility are in progress.


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