Worm Drive - Direction of Transmission

Direction of Transmission

Unlike with ordinary gear trains, the direction of transmission (input shaft vs output shaft) is not reversible when using large reduction ratios, due to the greater friction involved between the worm and worm-wheel, when usually a single start (one spiral) worm is used. This can be an advantage when it is desired to eliminate any possibility of the output driving the input. If a multistart worm (multiple spirals) is used then the ratio reduces accordingly and the braking effect of a worm and worm-gear may need to be discounted as the gear may be able to drive the worm.

Worm gear configurations in which the gear cannot drive the worm are said to be self-locking. Whether a worm and gear will be self-locking depends on the lead angle, the pressure angle, and the coefficient of friction; however, it is approximately correct to say that a worm and gear will be self-locking if the tangent of the lead angle is less than the coefficient of friction.

Read more about this topic:  Worm Drive

Famous quotes containing the words direction of and/or direction:

    As the unity of the modern world becomes increasingly a technological rather than a social affair, the techniques of the arts provide the most valuable means of insight into the real direction of our own collective purposes.
    Marshall McLuhan (1911–1980)

    The mountainous region of the State of Maine stretches from near the White Mountains, northeasterly one hundred and sixty miles, to the head of the Aroostook River, and is about sixty miles wide. The wild or unsettled portion is far more extensive. So that some hours only of travel in this direction will carry the curious to the verge of a primitive forest, more interesting, perhaps, on all accounts, than they would reach by going a thousand miles westward.
    Henry David Thoreau (1817–1862)