The gear train is the linked set of wheels and pinions inside a mechanical watch or clock. It carries the energy stored in the mainspring through the movement to the escapement. Because it speeds up rotation, a strong but slowly turning mainspring can keep a timepiece running for days or even weeks.
How does a gear train work?
Power starts at the mainspring, which supplies the energy for the whole movement. The main wheel is built into the mainspring barrel and turns with it. From there, power passes to the centre wheel and then on through the later wheels of the train. As it goes, the train speeds up the rotation. At the far end sits the escapement, which receives that energy. In clocks, a heavy weight can take the place of the mainspring. Watchmakers usually call the large gears wheels. Wheels mesh with pinions, and the shafts that carry both are called arbors.
What does each wheel do?
Some wheels in the train turn at set speeds. The centre wheel, also called the second wheel, makes one full turn every hour. In watches and clocks with the seconds hand in a subdial, the fourth wheel makes one full turn every minute. The escape wheel comes last. It keeps the balance moving, or the pendulum in a clock, by giving it a nudge each time it swings forward. This is where the train hands over the mainspring’s energy to keep the timepiece going.
Not to be confused with
The going train is not the only train in a timepiece. The motion work is a small, separate train that drives the hour hand from the minute hand. It uses a 12-to-1 reduction, so the hour hand turns once for every twelve turns of the minute hand. Striking clocks also have a striking train. It moves a hammer that sounds the hours on a gong. The going train is the one that carries power from the mainspring to the escapement.
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