An automatic or self-winding watch is a mechanical watch, whose mainspring is wound automatically by the natural motion of the wearer's arm, to make it unnecessary to manually wind the watch. Most mechanical watches sold today are self-winding.

To accomplish this, the watch contains a semicircular 'rotor', an eccentric weight that turns on a pivot, within the watch case. The normal movements of the user's arm and wrist cause the rotor to pivot back-and-forth on its staff, which is attached to a ratcheted winding mechanism. The motion of the wearer's arm is thereby translated into the circular motion of the rotor that, through a series of reverser and reducing gears, eventually winds the mainspring. Modern self-winding mechanisms have two ratchets and wind the mainspring during both clockwise and counterclockwise rotor motions.

The fully-wound mainspring in a typical watch can store enough energy reserve for roughly two days, allowing automatics to keep running through the night while off the wrist. Usually automatic watches can also be wound manually by turning the crown, so the watch can be kept running when not worn, and in case the wearer's wrist motions are not sufficient to keep it wound automatically.

Preventing overwinding.

A problem that had to be solved with self-winding mechanisms is that they continued working even after the mainspring was fully wound up, putting excessive tension on the mainspring. This causes a problem called 'knocking' or 'banking'. The excessive drive force applied to the watch movement gear train made the balance wheel rotate with too much amplitude, that is too far in each direction, causing the impulse pin to hit the back of the pallet fork horns. This made the watch run fast, and could break the impulse pin. To prevent this, a slipping clutch device is used on the mainspring so it cannot be overwound.

The watch winder.

For people who do not wear their automatic watch every day, watch winders are available to store automatic watches and keep them wound. This is particularly advantageous if the watch has complex complications, like perpetual calendars or moon phases. A watch winder is a device that can hold one or more watches and moves them in circular patterns to approximate the human motion that otherwise keeps the self-winding mechanism working. A mechanical watch should be kept wound and running as much as possible to prevent its lubricants from congealing over time, which diminishes accuracy. A full service (which involves disassembly, cleaning and re-lubrication) should be performed at least every five years to keep the movement as accurate as possible.


Master Watchmaker Gilbert Ó. Guðjónsson working on one of our Automatic movements this morning, JS Watch co. Reykjavik watch winder.

The source of this article is Wikipedia.