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THE BARREL ARBOR

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

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Figure 2: Diagram of a barrel arbor

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1. General description

The barrel arbor belongs to the Motor organ (power source) and constitutes the Axis of the barrel. It pivots most of the time between the Main plate and the Bridge of the barrel. Being closest to the energy source, the barrel arbor is the axis of a watch subjected to the greatest forces (torque). It is therefore naturally made of Steel and its pivots are of a large diameter.

At the center of the vertical plane of the Arbor lies its largest diameter: The Core. On the circumference of the Core is the hook to which the inner end of the Mainspring is fixed. The height of the Core corresponds to the height of the Mainspring plus a slight clearance allowing the spring to unwind freely. On either side of the Core are two pivot shanks that allow the Barrel drum to rotate freely around the Barrel arbor while the latter remains fixed, held in place by the Winding Click. The lower part of the Barrel arbor ends in the pivot that connects it to the Main plate. The Ratchet wheel can be placed below (as in our example) or above the Barrel bridge. The square of the Barrel arbor that receives the Ratchet wheel emerges directly from the upper part of the drum and then ends in its upper pivot connected to the Barrel bridge when the Ratchet wheel is located below the Barrel bridge. If the Ratchet wheel is located above the Barrel bridge, the positions of the square and the upper pivot of the Arbor are reversed. In such a case, the upper part of the Barrel arbor is drilled and tapped, with the Ratchet wheel fitting onto its square before being screwed into place.

2. Traditional manufacturing method

Although on the scale of a Movement the Barrel arbor is an Axis of generous dimensions, its manufacture involves two difficulties. The shaping of the hook on the periphery of the Core and that of the square intended to receive the Ratchet wheel. All operations can nevertheless be carried out on a Lathe (type 70). Except for the two difficulties mentioned, the Barrel arbor is a simple component made up of a stack of concentric turnings. The hook of the Core as well as the square can be made by Milling on an equipped Lathe or be the subject of a later operation on a Milling machine. The bravest will file the square by hand.

Once the Arbor is fully machined, the pivots can be rolled and the whole Arbor is Polished in order to protect it from corrosion and to limit friction with the other components of the Barrel.

3. Industrial production method

Like the drum and the cover of the Barrel, the Profile turning is undoubtedly the best process in terms of quality and cost. This manufacturing method is suitable for both small and large production runs.

Once the Arbor is fully machined, its pivots can be burnished and the entire Arbor is fully Polished to protect it from corrosion and limit friction with the other components of the Barrel.