STAR (WHEEL)

In watchmaking, the star wheel is a wheel, often solid, fitted with triangular or pointed teeth, designed to occupy stable, discontinuous positions rather than rotate continuously. A neck chain (sautoir), blade or spring-loaded lever, sits in the notch between two teeth and holds the star wheel in position until the next jump. This device is characteristic of mechanisms with display instantaneous or semi-instantaneous jumps, particularly calendar mechanisms: the date star wheel, the day star wheel, or the month advance by one step at a determined interval, ensuring a clean change of the indication. The Star (wheel) thus guarantees positioning accuracy and avoids ambiguous intermediate displays. Its geometry, the number and shape of its teeth, as well as the strength of the Neck chain (sautoir) must be carefully calculated to reconcile jump reliability with low energy consumption. Star (wheel)s are found in many calendar and striking complications.

Useful link:

– Astronomical indications