Jewel and Bushing Work

Every rotating pivot bears against a hole, and over years of running that hole — whether a jewel or a plain metal bearing — gradually wears from a perfectly round shape toward an oval one, as the pivot's rotation and the small side-loads transmitted through the train wear the hole preferentially along the direction of load. Wear is detected by inspecting the hole under magnification for visible ovality, and functionally by observing excessive or uneven end-shake and side-shake in the wheel that pivot carries, and by watching for a wheel that visibly tilts or wobbles as it turns rather than staying flat and true.

In a jewelled movement, the direct repair for a worn jewel hole is rejewelling: pressing out the worn jewel and pressing in a new one of the correct size, sourced to match the original hole diameter and the pivot's own diameter, so that the fit is neither loose (causing play and poor timekeeping) nor tight (causing friction and reduced amplitude). This is precise, exacting work, since jewel holes are sized in fractions of a millimetre and an incorrect fit can be worse than the wear it was meant to correct.

In an unjewelled bearing, or where a jewel setting itself (not just the stone) has become damaged or oversized, bushing is used instead: a small bearing bush, usually of brass or another suitable bearing metal, is fitted into the enlarged hole, itself re-drilled and reamed to the pivot's correct diameter, effectively restoring the original tolerance without altering the plate or bridge itself. Because bushing adds a small, later, and in principle removable component rather than altering original material, it is generally the preferred approach on historically significant or antique movements, in keeping with the conservation-minded preference for reversible intervention introduced in this academy's restoration lessons.

An alternative and generally discouraged shortcut — closing a worn hole by punching or burnishing the metal around it inward, rather than bushing or rejewelling — can restore a workable fit in the short term but does so by permanently deforming original plate material and typically produces a less durable and less concentric repair; it survives in some older repair traditions but is treated with caution in current professional and conservation practice for exactly the reasons that make bushing preferable.

Deciding between rejewelling, bushing, and (rarely) plate replacement requires judging the extent of wear, the value and significance of the piece, and the availability of correctly sized replacement jewels or bushing stock — a set of judgements that sits squarely within trained watchmaking practice, and one more example, alongside letdown and mainspring handling, of description here building comprehension rather than stand-alone competence to perform the repair.