The barrel is an assembly of watchmaking components that enables the proper operation of a mechanical watch movement. This part is the essential energy source for the operation of watch calibres.
The barrel: operation and composition
The barrel is made up of several different parts and forms a complex assembly.
A central arbor sits inside a mainspring, which in turn is housed in a hollow cylinder topped with a toothed wheel. The outer coil of the spring is attached to the barrel, while its inner coil is attached to the central arbor.
The barrel spring and its tension are the source of its action on the other components. It unwinds very slowly while transmitting energy to the entire gear train via the ratchet wheel (the barrel’s gearing). The gear train then passes the energy it has received to the escapement and the balance wheel. Note: in one hour, the barrel spring makes only one-ninth or one-sixth of a rotation!
Energy is delivered to the escapement and balance wheel assembly in a steady manner thanks to the barrel spring, which in turn depends on the escapement and balance wheel to prevent it from releasing its energy too quickly or at an irregular rate.
How is the barrel wound?
Winding the barrel spring is essential for it to function properly. It must be well wound at all times, as the energy that is then transmitted to other components—and sets them in motion—comes from its winding.
The barrel can be wound via a manual or automatic mechanical movement.
Manual winding is done using a winding stem, which must be turned to tighten the spring and therefore store energy.
Automatic winding is done using a rotor, or oscillating weight, in the form of a disc that turns with wrist movements to wind the barrel spring. It should be noted that in an automatic movement, the outer coil of the spring is not fixed. It is held in place by friction to avoid any risk of breakage. Indeed, the spring is wound continuously by the wearer’s movements.
Suspended or smooth barrel?
Depending on the watch model, there are suspended or smooth barrels.
The mainplate—the plate on which all the components are mounted—is connected to the upper part of the suspended barrel.
The smooth barrel, for its part, has no toothed wheel. A chain connects it to the fusee of the movement in fusee watches.
