Last Updated on May 22, 2024 by Jason

The wheel train in a mechanical watch is a key component of the movement that transfers energy from the mainspring to the escapement and ultimately, the hands. This intricate system of gears and wheels works together to manage the energy distribution and regulate the movement of the watch hands. Together, the mainspring, wheel train and the escapement ensure that the watch keeps accurate time.

Watch movements are very standardised, and the wheel trains of most watches have the same components. The large gears in watches are generally called wheels and the smaller gears they mesh with are called pinions. The shafts that the wheels and pinions are mounted on are called arbors (axles). The wheels are mounted between the movement plates, with the pivots rotating in jewelled holes in the plates. Typically, a mechanical watch has one wheel train responsible for timekeeping, this is often referred to as the going train. However, some watches may have additional gear trains for complications like chronographs or calendars.

Note: The wheel train is also known as the gear train.

The main components of the wheel train

The wheel train in a watch movement consists of several key components that work together to transmit power from the mainspring to the escapement. The key parts are:

Wheel train components.
Wheel train components. © Encyclopedia Brittanica.
  1. Mainspring: The coiled metal spring that stores energy when wound. The mainspring powers the watch. The mainspring can be wound manually or by a self-winding system, known as an automatic.
  2. Barrel: Contains the mainspring and regulates the release of power. The mainspring barrel is actually the first wheel in the gear train and connects to the centre wheel via a series of teeth on the outside of the barrel.
  3. Centre wheel: Connects to the barrel The centre or second wheel turns once per hour and drives the third wheel. The centre or second wheel turns once per hour. Its arbor projects through a hole in the dial and drives the cannon pinion, which carries the minute hand. The centre wheel also drives a component called the motion work. This is a 12 to 1 reduction gear that drives the hour hand from the minute hand.
  4. Third wheel: Transmits power from the centre wheel to the fourth wheel.
  5. Fourth wheel: The fourth wheel rotates once per minute and drives the second hand. The fourth wheel also turns the escape wheel pinion.
  6. Escape wheel: The escape wheel is released one tooth at a time by the escapement, with each swing of the balance wheel. The escape wheel keeps the balance wheel oscillating by giving it a small push each time it moves forward, this power is transferred using the pallet fork.
  7. Pallet fork: Controls the release of energy to the balance wheel, which in turn, regulates the timekeeping of the watch.

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