THE OMEGA CO-AXIAL:
AN IMPRESSIVE ACHIEVEMENT

By Walt Odets

At the 1999 Basel Watch and Jewelry Fair, Omega announced a new watch for the DeVille line: a chronometer-rated, limited edition watch. Although based on the Omega caliber 2500, an ETA 2892 derivative, the watch would, remarkably, be supplied with a co-axial escapement and free sprung balance. Not only would this be the first co-axial escapement available in a watch selling for less than US$150,000, the Omega was presented from the beginning as a harbinger of regular, large-scale production of watches beating to this George Daniels' design. The announcement seemed news of a new era in mechanical watch making. Initially, 1,000 yellow gold, 1,000 red gold (pictured, right), and 100 platinum watches would be produced.

THE CONCEPT

The conventional lever escapement has performed duty in fine mechanical watches for more than two centuries. Invented by the British maker Thomas Mudge, and further refined by the Swiss, the design has proved robust, reliable, and capable of regulating a watch in use (and thus subject to variable and sundry accelerations) to about three seconds per day. The design relies heavily, however, on sliding friction as the escape wheel impulse surfaces sweep over the pallets to power the balance. Sliding friction means lubrication, and lubrication has always been the Achille's heel of the lever escapement. While I believe that contemporary synthetic lubricants (most notably the Moebius 9415 pallet grease) have ameliorated the problem to some extent, it certainly remains an issue. Sliding friction (as opposed to rolling friction) is always undesirable.


A locking pallet on the lower escape wheel of the Omega Co-axial.

 

 

GEORGE DANIELS

George Daniels, arguably a more important student of watchmaking than watchmaker per se, has kept the British in the forefront of horological theory. He has studied escapement design for nearly half a century. Beginning with Breguet's echappement naturel, and proceeding through a number of other designs, Daniels has been pursuing a single objective: the elimination of lubrication at the impulse surface. In the co-axial escapement, this is accomplished with a largely rolling (as opposed to sliding) impulse to the balance. The impulse friction in such a radial design is reduced by more than the radial nature of the geometry. The length of sliding or rolling contact in a radial design is a fraction of that in a lever design--approximately seven percent. An important additional advantage provided by the co-axial design is the smaller lift angle and increased arc of free vibration of the balance wheel. A much greater part of the total arc is conducted free of interfering contact with the pallet lever. Such contact compromises the physics of the balance-spring unit.


THE OMEGA MOVEMENT

Omega has based its caliber 2500 co-axial on the venerable Omega caliber 1120. Based on the ETA 2892, Omega has long added two jewels to the ETA design for the bi-directional, click-wheel automatic winding system. The escapement of the 2500 adds another two jewels, and another two are added to the mainspring barrel for a total of 27. The movement is 12.5 lignes (27.2 millimeters in diameter), and 3.6 millimeters thick. Omega cites a power reserve of 44 hours, typical for single-barreled automatic movements of this size.

Largely because of finishing differences, the Omega caliber presents a somewhat different appearance than that of a more standard 2892.

The automatic winding system of the 2892 is largely contained within a module that lies under, and is attached to, the winding bridge itself.

Bidirectional winding is accomplished through the double click-wheel system, introduced by Eterna in 1948, and now utilized throughout the ETA line.

With the winding rotor and bridge removed, the handsomely executed caliber is now completely visible. There is however, still sparse evidence of the technical innovation within.

Sliding friction in a lever escapement.

Radial friction in a co-axial escapement.

CONTINUE TO PART 2 OF THE ARTICLE


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