A crown wheel is the toothed wheel in a watch’s winding mechanism that passes torque from the crown to the ratchet wheel. It is the last moving part but one in that mechanism. Its job is to carry winding energy onward through the winding train.
How does a crown wheel work?
Torque from the crown reaches the crown wheel through the winding pinion. The pinion’s outer teeth mesh with the crown wheel, which sits beside the ratchet wheel and links the two. On the way, the crown wheel changes the plane of motion. The winding pinion turns in a vertical plane, while the crown wheel and the ratchet wheel turn in a horizontal one. To make this change, the crown wheel has two sets of teeth. One set is cut at a 45° angle on its underside, where it meshes with the winding pinion.
How is a crown wheel made?
The winding train carries high forces. For this reason, the crown wheel turns on a core that is as wide as possible. When made by hand, the crown wheel can be produced entirely on a lathe fitted with a dividing plate. That covers both sets of teeth, including the angled ones on the underside. No other machine is needed for the work.
Where it comes from
The crown wheel’s appearance, and so in effect its invention, is linked to the keyless winding system that Adrien Philippe introduced in 1842. The name probably comes from the wheel’s double toothing, whose two sets of teeth give it the look of a crown. The same name also belongs to an older part, described below.
Not to be confused with
In old timekeepers, crown wheel means something else. It is the crown-shaped escape wheel of the verge escapement, the earliest mechanical escapement. That wheel belongs to the escapement, not to the winding mechanism. In verge watches it had to be made very small. So the same term names two separate wheels, one for winding and one for the escapement.
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