In horology, a wheel train (or just train) is the gear train of a mechanical watch or clock.[1] Although the term is used for other types of gear trains, the long history of mechanical timepieces has created a traditional terminology for their gear trains which is not used in other applications of gears.

Watch movements are very standardized, and the wheel trains of most watches have the same parts. The wheel trains of clocks are a little more varied, with different numbers of wheels depending on the type of clock and how many hours the clock runs between windings (the "going").[2] However, the wheel trains of clocks and watches share the same terminology, and are similar enough that they can be described together. The large gears in timepieces are generally called wheels, the smaller gears they mesh with (large to small, large to small) are called pinions, and the shafts that the wheels and pinions are mounted on are called arbors.[3] The wheels are mounted between the plates of the movement, with the pivots rotating in holes in the plates. The pivot holes have semicircular depressions around them, called oil cups, to hold the oil in contact with the shaft by capillary action. There are several wheel trains in a typical clock or watch.

Going train

Pocket watch with gears labelled.

The going train is the main gear train of the timepiece. It consists of the wheels that transmit the force of the timepiece's power source, the mainspring or weight, to the escapement to drive the pendulum or balance wheel.[4] The going train has two functions. First, it scales up the speed of rotation of the mainspring or weight pulley. This allows the use of a very strong, slow turning mainspring or heavy weight that will run the timepiece for days or weeks. Second, its gear ratios divide the rotation of the escape wheel into convenient time units of seconds, minutes, and hours, to turn the timepiece's hands. The going train wheels are the only ones under load in a timepiece, since they bear the constant torque of the mainspring which is applied to the escapement, so these wheels are the only ones that receive significant wear.[5] In watches and some high quality clocks their arbors have jewel bearings. The going train in a modern clock or watch consists of:

Motion work

Motion work of a clock, showing (f) center wheel, (x,b) cannon pinion, (x') minute wheel, (y,c) hour wheel, (t) hour hand, (m) minute hand.

The motion work is the small 12-to-1 reduction gear train that turns the timepiece's hour hand from the minute hand.[6][7] It is attached to the going train by the friction coupling of the cannon pinion, so the minute and hour hands can be turned to set the time. It is often located on the outside of the movement's front plate, just under the dial. It consists of:

Keyless works

Used in watches, the keyless works are the gears that wind the mainspring when the crown is turned, and when the crown is pulled out allow the hands to be set.[8][9] The term originated because, before the modern form of keyless works was invented by the French watchmaker Adrien Philippe in 1843, watches were wound and set by inserting a separate key into holes in the back and turning it.[10] The core of the keyless mechanism is a gear on the watch's winding stem, the clutch (or castle wheel in Britain), with two sets of axial gear teeth on it, which slides in and out. When the stem is pushed in, a lever slides the clutch out, and the outer set of teeth engages a small wheel train which turns the mainspring arbor, winding the mainspring. When the stem is pulled out, the clutch slides in, and the inner teeth engage another wheel, which turns the hour wheel in the motion work, turning the watch's hands.

Striking train

In striking clocks, the striking train is a gear train that moves a hammer to strike the hours on a gong. It is usually driven by a separate but identical power source to the going train. In antique clocks, to save costs, it was often identical to the going train, and mounted parallel to it on the left side when facing the front of the clock.[11]


  1. ^ "Mechanical clock: p.3 The wheelwork". Encyclopædia Britannica online. Encyclopædia Britannica Inc. 2008. Retrieved 2008-07-06.
  2. ^ Milham, Willis I. (1945). Time and Timekeepers. New York: MacMillan. p. 178. ISBN 0-7808-0008-7.
  3. ^ Britannica 2008
  4. ^ Odets, Walt (2004). "The Wheel Train". Illustrated Glossary of Watch Parts. TimeZone Watch School. Retrieved 2008-07-05.
  5. ^ Hahn, Ed. "Are more jewels better?". Sec. 1.1.5 Mechanical Watch FAQ v.1.0. Retrieved 2008-07-02.
  6. ^ Milham 1945, p.113-114
  7. ^ Odets, Walt (2004). "The Motion Works". Illustrated Glossary of Watch Parts. TimeZone Watch School. Retrieved 2008-07-05.
  8. ^ Odets, Walt (2004). "The keyless works". Illustrated Glossary of Watch Parts. TimeZone Watch School. Retrieved 2008-07-05.
  9. ^ Hillmann, B. (2004). The Keyless Mechanism, a Practical Treatise on its Design and Repair. p. 26.
  10. ^ Odets, Walt (2004). "The keyless works of a Watch". The Horologium. Retrieved 2008-07-05.
  11. ^ Milham 1945, p.198