The watch balance wheel is one of the most important components of watchmaking mechanics. Thanks to its oscillations, it ensures the precision 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 itself received it from the mainspring barrel.
It is not always known, but a mechanical watch balance wheel does not resemble a clock pendulum… How then can one recognize each component, and what differentiates them?
The Watch Balance Wheel: Definition
One does not need to be a watch enthusiast to recognize the characteristic tick-tock of a pendulum clock! But did you know that it is the balance wheel that is responsible for this little melody?
This regulating organ is generally circular in shape, and it is a mobile 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 movements accompanied by the small tick-tock. These movements allow time to be divided into equal intervals, namely seconds.
The Balance Wheel of a Watch
The balance wheel of a mechanical watch resembles a small flywheel with two or three arms that allow for perfect balance of the component. The balance wheel comes paired with a hairspring that is positioned right in the middle of the balance wheel. This very fine spring contracts upon itself to balance the force sent to the balance wheel by the escapement’s lever.
The balance wheel operates as follows:
- The TICK is generated by the rotation of the balance wheel, which is caused by the impulse from the escapement’s lever.
- The hairspring (also called balance spring) compresses to balance the energy received from this impulse.
- The hairspring then expands, allowing the balance wheel to return with a small TOCK.
- Once this back-and-forth movement is completed, the escapement’s lever gives a new impulse to the balance wheel, and the process restarts.
The speed of the balance wheel is measured in Hertz, and it is calculated based on the oscillation frequency.
Quartz watch balance wheels do not have a hairspring. Instead, a tiny electric motor generates regular oscillations for the balance wheel.
The Clock Pendulum
Although a clock pendulum is mobile, just like its mechanical watch counterpart, it generally takes a different form. Its function, however, is identical: to provide precision to the watch mechanism!
The pendulum and the foliot are two different types of regulating mechanisms found in clocks.
The pendulum takes the form of a vertical rod equipped with a weight that oscillates from left to right. It is thanks to the pendulum’s weight that the oscillation occurs regularly. This regulating mechanism is often made of steel or brass, and is generally round in shape.
The foliot is a balance mechanism dating back to the 14th century. Its shape is also long and thin, as it consists of a weight suspended from a chain or rope, which is itself connected to the foliot. The pendulum was preferred over it from the 17th century onwards.