Components › Movement

THE BARREL DRUM

MENU

Figure 1: Exploded view of the barrel (motor organ (power source))

Click on the animation to enlarge it

Figure 2: Diagram of a barrel drum for manual winding

Click on the thumbnail to enlarge it

1. General description

The barrel drum is one of the four components that make up the barrel, which is themotor organ (power source) of a mechanical watch. It is a hollow cylinder made of brass or German silver inside which the mainspring is housed. A peripheral toothing occupies about 1/5^th of the total height of the drum. It meshes with the wings of the centre pinion and thus distributes the barrel’s energy to the entire movement. The barrel drum is pierced at its centre to allow the end of the arbor to pass through. The arbor must be free within this hole so that it can pivot freely between its pivots during the winding of the watch (winding up) and so that the drum can pivot around the arbor during letting down (running of the watch). A drop is present inside the drum around the periphery of the hole through which the arbor passes. A similar drop is found inside the barrel cover / lid. These two drops make it possible to control the shake (play) in height of the barrel drum and to limit friction between the arbor and the barrel drum.

An unlocking (drop angle) is milled inside the wall of the barrel drum. It allows the mainspring’s bridle to hook onto it so as to pull the barrel in its rotary motion.

The machining of the unlocking (drop angle) intended for the cover includes a slight angle so that the cover can clip into place.

The visible face of the drum offers a significant surface that is traditionally decorated with a Sunburst finish or a Snailing. Finally, the Barrel drum – like its Barrel cover / lid – is protected from oxidation by a galvanic treatment (Gilding, Rhodium plating) or PVD.

2. Artisanal manufacturing method

The artisanal manufacturing of a Barrel drum can be entirely carried out using a Lathe (type 70). After turning the outer diameters (outer diameter of the drum and total diameter of the toothing) while respecting their height, the inside of the drum can be turned and hollowed out. During these operations, care is taken to respect the diameter and height of the Drop in addition to the depth dimensions and diameters to be respected. The notch intended to receive the barrel cover / lid can be made simply by tilting the axis of the carriage holding the Graver. Finally, it is possible to make the unlocking (drop angle) of the spring bridle with the help of the lathe’s milling accessory and a milling cutter with a suitable profile. While most craftsmen prefer to then machine the toothing using a cutting machine, it is also possible to carry out this operation on the lathe with the milling accessory. All that remains is to turn the drum over in the lathe’s chuck and true its last face, while bringing its thickness to its final dimension.

Finally, the Barrel drum can be decorated (Circling, Sunburst finish, Snailing, etc.) using the Lathe or dedicated machines before receiving its surface treatment (galvanic or PVD). Its manufacturing is then complete.

3. Industrial production method

Due to the cylindrical shape and dimensions of the Barrel drum, Profile turning is the ideal solution for producing Barrel drums in series, regardless of the required quality level and the quantity to be produced. With the exception of Decoration, all operations – including gear cutting – can be carried out on an Automatic lathe.

Finally, the Barrel drum can be decorated (circling, sunburst finish, snailing, etc.) using the lathe or dedicated machines before receiving its surface treatment (galvanic or PVD). Its manufacturing is then complete.