How Old Are Gears?

Gears are one of the oldest pieces of equipment known to man. They date back to at least the 4th century B.C. Inventors used them in waterways and clocks. After a long period of time, a major development came about in the 17th century to provide constant velocity ratios.

The 19th century saw the first use of form cutters and rotating cutters. The direction of rotation is reversed when one gear turns another.