Wheel Train Bridge

The Horologium September 16, 2002 admin




JLC bridgeThe wheel train bridge carries the upper pivots of the
center wheel (usually), third wheel, fourth wheel, and, sometimes, the escape wheel. The JLC bridge (1A) shows first-class finish. In addition to the sturdy construction and very fine machining, which provides good alignment for the wheel train, all edges are anglaged (or chamfered, as show at the blue arrow). The anglange provides a much more refined appearance to the watch and eliminates sharp edges that can chip or scratch other movement parts during servicing. The jewel holes (yellow arrow) show a full decouverture, the angled area around the jewel hole. The decouverture, which makes jewel replacement easier is highly polished, enhancing the beauty of the jewel. (In some very fine movements, depending on taste, the
decouverture may also be gilded.) The bridge screws are also nicely recessed (red arrow) and the recesses or moulding (also oeil de perdrix, or partridge eye in French) are extremely well polished. Unlike the two other movements, all bridge screws are chamfered on all edges and completely polished to a mirror, almost black finish. The JLC bridge is fully and artfully decorated with cotes de Geneve (or Geneva bars), the striped pattern of alternating reflectivity seen across the entire bridge surface. The rhodium plating (which is seen in most fine movements and is preferable to gilding for durability) is even and of excellent, whitish color. Though barely visible under the finish, the grain of the steel is fine, even, and straight.

Eterna bridgeThe Eterna bridge (1B), as with many automatics (and all ETA automatics) uses a bridge that supports both automatic winding gear and the wheel train. It is thus different in appearance than a traditional train bridge. This Eterna bridge is well constructed and decently finished, functionally speaking. Jewel holes (not visible in un-illustrated sub-bridges) have only slight or no decouverture, and only minimal finishing and polishing are evident. There is moulding around the bridge screws (red arrow), but it is entirely unpolished. The lack of anglage (blue arrow) and polishing (yellow arrow) is apparent. The
rhodium plating lacks the evenness and good color (it is too gray) of the JLC bridge. Finally, the grain of the steel is relatively coarse and uneven.

Tissot bridgeThe Tissot finishing is absolutely basic, although it is dishonestly elaborated with gilding and a very poorly executed imitation of cotes de Geneve. The decouverture around the jewel holes (blue arrows) is slight and unpolished and there is no anglage. Mouldings are unpolished. The silk screening of markings is less expensive than the engraving used for better movements and lends a particularly unappealing quality to this part.