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This documentary examines the evolution of gear technology and the uses of gears from their invention to modern day applications.

The gear provides the best means for the efficient transfer of power from one direction to another. Today they are most widely used in the control of speed, which is determined by the respective number of teeth on each gear called the gear ratio.

The earliest example was the Chain of Pots, first used 2000 years ago. The mechanism worked through crude spun gears raising a horizontal force of water vertically, resulting in the flowing water providing power. Then, from its beginnings in the first century, the vertical or Roman mill, became the major source of power for the next 1800 years. The gears used in the windmills and water mills that powered 13th century industry, were crudely constructed using wood. From the middle of the 14th century, mechanised clocks containing metal gear wheels appeared in Europe. It was established that continuous rolling contact could reduce friction between gear teeth increasing efficiency and reducing wear. Initially the cycloid shape was used, but the involute curve, first proposed in the 18th century, has since become universally accepted as the best profile for gear teeth.

The Industrial Revolution brought the widespread use of steam engines. Belts, chains and gears were required to transfer their power. As more powerful engines were developed, gear wheels had to take greater loads. The use of cast iron, the correct tooth shape and adequate lubrication became vitally important.

In many industrial machines spur, bevel and worm gears were used to transfer power, and the compact gear provided high gear ratios. Gear cutting machinery became more accurate and in the 1840s, the principle of gear generation was first applied in the USA.

The differential gear appeared for the first time on the road in a tricycle and is now a standard feature of the motor car. Today, the internal combustion engine and steam turbines like the one used by Charles Parsons (1854-1931) in the first turbine powered ship in 1897, involve high gear ratios and use single or double helical gears. These are smoother, quieter running and suffer less wear.

Motor vehicles and early industrial machines requiring a range of gears used the synchro mesh gearbox. Only the gear in use drives the shaft, while the rest rotate freely. James Watt (1736-1819) originally devised the sun and planet gear in 1871, in which gear wheels of varying size convert vertical piston movement into rotary motion. More recently, the principle has been used in the epicyclic gearbox, which can handle very high power loads.