Geartrains
A classic clock geartrain has a number of arbours with toothed wheels. It starts with a drum where the power source acts: a spring wound inside the drum or a rope wound around the drum from which a weight is suspended.
On that arbour is also a great wheel, usually with spokes, which drives the other arbours of the train. The other arbours each carry a small pinion and a large wheel, the pinion being driven by the large wheel of the previous arbour, the large wheel driving the pinion of the next arbour.
The train ends in an escape wheel, which advances tooth by tooth through the action of the escapement mechanism, regulated by a pendulum.
In older clocks the escapement may be a crown wheel working with a verge and foliot instead of a pendulum. There may also be pinions of the lantern type: pins between two discs instead of teeth on a cylinder.
The period of rotation of each arbour is directly computable from the time taken by the escape wheel to make one full turn. The train has one arbour which drives the clock's hands and therefore turns at a multiple of one hour.
A train is completely defined by the number of teeth of each of its wheels (large, pinions, escape/crown). This page creates a diagram of a train from its specifications as given in the table below. A minimum of two and a maximum of six arbours can be specified. For each arbour only the number of teeth needs to be given: usually the teeth on all wheels are of identical or very similar size; therefore a useful diagram, if dimensionally perhaps not completely accurate, can be drawn by assuming all teeth are identical. Similarly, for simplicity all arbours are assumed to have the same diameter.
For each pinion a choice between the lantern or normal pinion form is available and for the escape wheel there is a choice between a crown shape or the normal anchor escape wheel.
The size of the drum is given by the number of teeth it would have if it were a toothed wheel.
Lastly, to compute the rotation periods, the number of seconds for a full rotation of the escape wheel needs to be given. This is the only number that does not need to be an integer.
The button "draw train" will then draw the train. Wheels on alternate arbours have different colours for the purpose of more easily distinguishing them. It is assumed that the escape/crown wheel turns clockwise in the drawing.
At first display of the page, an example of a train is shown; it is from a classic longcase "comtoise" clock that ticks away in our house.