The animation below shows the comparison between a double start worm and the single start worm. The two start worm would then behave like a two-toothed gear. In total, two teeth of the worm wheel would have moved on. On the other hand, with one revolution of a two start worm, two worm threads would each move one tooth further. Compared to a toothed wheel, in this case the worm actually behaves as if it had only one tooth around its circumference. The worm gear is thus moved on by one tooth. With one rotation of the worm the worm thread pushes straight on by one position.
That the number of starts of a worm corresponds to the number of teeth of a cog wheel can also be seen clearly from the animation below of a single start worm drive. Since the number of starts is of a worm ultimately the equivalent to the number of teeth of a toothed wheels, the number of teeth to be used to determine the transmission ratio \(i\) corresponds to the number of starts of the worm: Worms are basically spirally wound “teeth” that screw into the worm gear and drive it! Transmission ratio In general, mainly single start worms are produced, but in special cases the number of starts can also be up to four. Correspondingly, one speaks of a single start worm, double start worm or multi-start worm. The “number of teeth” of a worm is referred to as the number of starts. Animation: From two toothed gear to double start worm This would then correspond to a “double-toothed” worm (two thread worm) or a “multi-toothed” worm (multi thread worm). One could now imagine that instead of one tooth, two or more teeth would be wound around the cylindrical gear at the same time. Animation: From single toothed gear to single start worm The result would then be a “single-toothed” worm.
Now increase the helix angle (lead angle) so much that the tooth winds around the gear several times. Imagine there was only one tooth on a helical gear. The worm can be regarded as a special case of a helical gear. Such a gearbox, consisting of worm and worm wheel, is generally referred to as a worm drive. The mating gear to the worm is the worm gear. In this case, the tooth winds around the worm shaft like the thread of a screw. A special design of the gear wheel is the so-called worm.
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