GEAR

A gear is the assembly formed by two toothed wheels in mesh, used to transmit a Movement rotational movement and to modify its speed and torque. It is the basic element of the Train (wheel train) of a Movement Horologist (watchmaker). Generally, a small wheel — the pinion — meshes with a larger wheel; the ratio between their numbers of teeth (gear ratio) determines the reduction: the finishing train reduces the energy from the Barrel to the Escapement by accelerating the wheels, while the Motion work, by contrast, steps down to obtain the 1/12 and 1/60 ratios between hands. The quality of a Gear depends on the profile of the teeth (often involute or epicycloidal profile in horology), the Distance of centres, the operating Set and the surface finish, which determine the efficiency and smoothness of transmission. Poorly cut teeth, an incorrect Distance of centres or excessive play cause binding, jerks, or even disengagement. The care given to the Gears directly affects the energy efficiency of the Movement, and therefore the Amplitude of the Balance and the accuracy.