Model: 072 Worm and Gear
The worm or continuous screw on the horizontal shaft is the driver. This combination reduces the speed of the driven member and also multiplies its power. The power increases proportionally as the speed decreases. The speed ratio of shafts depends upon the relation of number of threads on the worm (single or multiple) to the number of teeth in the worm wheel or gear. This type of speed reducer is used between shafts at right angles to each other.
[Virginia Downward & William M. Clark, 1930]

[Editor’s Note: The worm drive is also called the 'endless screw'. This mechanism goes back many centuries and was used in the Renaissance and can be found in the notebooks of Leonardo da Vinci {Codex Madrid}, and Francesco di Giorgio of Siena. When the large gear has planar teeth, the worm drive is usually not back-driveable, i.e., only the small screw can act as the driver. If the large gear has helical teeth then it is possible for the large gear to drive the smaller gear. FCM]

Francis Moon 2005-00-00

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