Wheel train

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The wheel train is part of the watch movement, containing all of the geared wheels that drive the hands and complications. These gears transfer torque from the barrel to the escapement wheel.

The wheels are usually held in place by bridges or cocks connected to a plate. High-torque wheels are usually anchored with jewels (and sometimes chatons) though other wheels may rest in simple holes. The balance wheel usually also has an anti-shock device to anchor its staff.

The wheel train includes:

Going train

Uhrwerk Illustration2.jpg

The main gear train of the timepiece is known as the going train. These wheels transmit torque from the mainspring to drive two primary functions:

  1. They drive the rotation of the hands and other complications
  2. They power the balance wheel

The going train consists of three or four main gears or wheels:

  • The second wheel (Z1) turns once per hour to drive the motion work which turns the hour and minute hands. In traditional movements (which place the seconds in a secondary dial), this is at the center. It is called the second wheel because it is the second wheel in the gear train after the barrel. It it is often also referred to as the center wheel.
  • The third wheel (Z3) drives the pinion for the fourth wheel or, for clocks which lack a fourth wheel, drives the escapement wheel directly.
  • The fourth wheel (Z5) drives the seconds subdial and escapement wheel. It is sometimes dispensed with in modern movements, with central seconds driven by the motion work and the escapement driven by the third wheel directly. Because of its function, this is also sometimes called the seconds wheel, though it is easy to confuse this for the second wheel noted above.
  • The escapement wheel (E) moves one tooth at a time, kept in time by the escapement. It also powers the escapement.

Motion work

The motion work moves the hands and is driven by the second wheel (also often called the center wheel). It includes a 12:1 reduction gear train to drive the hour hand from the minute hand and is often located just behind the dial.

The motion work consists of the following gears or wheels:

  • The cannon pinion holds the minute hand. It is usually friction fit over the center shaft
  • The minute wheel drives the hour wheel
  • The hour wheel fits over the shaft of the cannon pinion and holds the hour hands

See Also