Balance wheel

The watch balance wheel is one of the most important components in watchmaking mechanics. Thanks to its oscillations, it ensures the accuracy of the mechanical movement by moving within the watch mechanism to balance and control the energy received from the gear train via the lever escapement, which in turn receives it from the mainspring barrel. It is not always widely known, but the balance wheel of a mechanical watch does not look like a clock pendulum… So how can each component be identified, and what sets them apart?  

The watch balance wheel: definition

  You do not need to be a watchmaking enthusiast to recognize the distinctive tick-tock of a clock! But did you know that the balance wheel is the source of this little melody? This regulating organ is generally circular in shape, and it is a moving part that plays a very important role in the mechanical movement. By oscillating on its axis of rotation, the balance wheel creates back-and-forth motion accompanied by the small tick-tock. These movements divide time into equal intervals, i.e., seconds.  

The balance wheel of a watch

  The balance wheel of a mechanical watch resembles a small wheel with two or three arms that ensure perfect balance of the component. The balance wheel is paired with a hairspring (also called a balance spring) positioned right in the center of the balance wheel. This extremely fine spring coils in on itself to balance the force transmitted to the balance wheel by the escapement lever. The balance wheel works as follows:

1. The TICK is produced by the rotation of the balance wheel generated by the impulse from the escapement lever
2. The hairspring (also called a balance spring) compresses to balance the energy received through this impulse
3. The hairspring then relaxes, allowing the balance wheel to swing back with a small TOCK
4. Once this back-and-forth motion is completed, the escapement lever gives the balance wheel a new impulse and the process starts again

The speed of the balance wheel is measured in hertz, and it is calculated based on the oscillation frequency. The balance wheels in quartz watches do not have a hairspring. Instead, there is a tiny electric motor that generates regular oscillations for the balance wheel.  

The balance wheel of a clock

  Although the balance wheel of a clock is mobile just like its counterpart in mechanical watches, it generally takes a different form. Its function is nevertheless identical: to bring accuracy to the timekeeping mechanism! The pendulum and the foliot are two different types of balance regulators found in clocks. The pendulum takes the form of a vertical rod fitted with a weight that swings from left to right. It is thanks to the pendulum’s weight that the oscillation occurs regularly. This regulator is often made of steel or brass, and is generally round in shape. The foliot is a balance regulator dating back to the 14th century. Here too, its shape is long and slender, as it consists of a weight suspended from a chain or cord, itself connected to a foliot. From the 17th century onward, it was replaced by the pendulum.