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Design and Application of the Worm Gear

William P. Crosher
William P. Crosher
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ASME Press
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Thousands of years ago, a section of tree trunk was the first device used to convert sliding friction to rolling friction. Did that section of tree trunk then evolve into the first wheel? We do not know for sure when the wheel arrived, but the invention changed the application of energy. The earliest known wheel was used on the banks of the Euphrates sometime around 4000 B.C. It was a remarkably precise, symmetrical, and solid construction. Progressive stages of wheel development can be observed through many centuries. Prior to the arrival of Columbus, the Native Americans knew of the principle, but they found no practical use for such a contrivance. In other regions its use was restricted by the terrain, such as sand.

As necessary as the wheel is to our culture, it was quickly discovered that efficient machines need wheels with teeth or “gears.” Gears are essential for the positive transmission of power between shafts. Toothed wheels rotate about axes, whose relative position is fixed, with one wheel imparting motion to another. Devices could not be synchronized without such a mechanism. In 4000 B.C., gearing was utilized for hoisting loads. By 2,600 B.C. gearing had been developed to the stage whereby complex differentials were in use.

The period of Alexander the Great, 400 B.C., was the first of the three great periods of technical advancement, the others being the Renaissance and the present. During these periods, we know that transport, inventions and research go through accelerated development. In the first period, metal working techniques advanced, iron began to take the place of bronze. (Alexander was the first man known to wear an iron helmet.) His tutor, Aristotle (384–322 B.C.), also made significant contributions to science and engineering.

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