DRUM COVER
It is one of the four components of the barrel, which itself is the driving organ of a mechanical watch. As its name suggests, the drum cover closes off the barrel drum by clipping onto it, protecting the mainspring from dust. The drum cover is made of the same material as the drum (either brass or nickel silver). In rare cases, such as in ultra-thin or skeletonised watches, the drum cover may be skeletonised or entirely omitted.
As a simple disc made of brass or nickel silver, the drum cover can be entirely machined on a lathe (such as a type 70). Like the barrel drum, a small drop-shaped protrusion is positioned at the centre of the cover. This defines the vertical endshake between the barrel and its arbor, while reducing friction points between the two components. The outer diameter is machined at an angle to allow the cover to snap into its seat inside the drum, which is itself turned with the same angular value.
Two notches are usually cut around the edge of the cover — either milled or filed later on. These notches are used to open a closed barrel. Decorative operations (such as circular graining) can also be carried out on the lathe or with dedicated machines. Once decorated, the drum cover may undergo surface treatment (galvanic or PVD). At this stage, its manufacture is complete.
As with the barrel drum, bar turning is the most efficient production method for the drum cover in terms of both quality and cost, especially since it has no toothing. Its manufacturing process is quick and poses no particular difficulty.
Decorative operations (such as circular graining) can be carried out using dedicated machines. Once decorated, the cover may receive its surface treatment (galvanic or PVD), after which its production is complete.