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THE CRYSTAL-FITTING STAKE

The crystal-fitting stake is the Bench tool intended for the fitting and removal of crystals in a watch Case. It takes the form of a small lever press, whose frame receives, at its two ends, interchangeable blocks, with a profile and diameter suited to the shape of the Crystal (watch glass) and to the geometry of the Bezel. Depending on the case, its function consists of slightly compressing the Crystal (watch glass) to insert it into its housing, of fitting a tension-ring crystal, or of releasing an existing Crystal (watch glass) for replacement. The diversity of Case constructions — snap-fit crystal, tension-ring crystal, screwed-in crystal, glued-in crystal — and the variety of Materials used justify the existence of specific tooling.

The instrument consists of a vertical frame made of machined Metal or Aluminium Smelting, and a slide controlled by a lever or a Screw. The slide and the base of the frame each receive a block — a circular support piece, with an active face either concave or convex, supplied as a Set to cover the range of Crystal (watch glass) and Case diameters. During fitting, the Case rests on the lower block, which holds it flat; the Crystal (watch glass), presented on the upper block, is gradually brought into contact with the Bezel by lowering the slide. The applied pressure is manually adjusted via the lever, and the Horologist (watchmaker) visually checks the even seating of the Crystal (watch glass) around its entire circumference.

The stakes constitute the functional core of the crystal-fitting stake and are supplied in sets comprising several dozen pieces. The concave stakes are used for fitting domed crystals, allowing them to fit within the concavity without central marking; flat or convex stakes are used for flat crystals and for certain disassembly operations, when pressure must be transmitted onto the shoulder of the crystal rather than onto its face. Specific stakes are provided for tension-ring crystals, whose fitting requires prior compression of the crystal-ring assembly before its insertion into the bezel. The stakes are generally made of synthetic material or Aluminium, so as not to mark the crystal, and their diameter is engraved on their underside to facilitate identification.

The crystal-fitting stake is used for every operation involving the replacement or restoration of a crystal: substituting a scratched acrylic crystal, fitting a new mineral crystal onto a case under servicing, mounting a sapphire crystal with a sealing gasket. The safety of the gesture depends on selecting the die matching the exact diameter of the housing, the perfect centering of the case and the crystal on the axis of the press, and the regularity of the pressure applied by the lever: excessive or poorly centered force will crack a sapphire crystal, split an acrylic crystal, or mark the edge of the bezel. Like other tools dedicated to casing work, the crystal-fitting stake does not directly contribute to the movement, but it determines the water resistance and final quality of the assembled piece.