By Walt Odets
The co-axial escapement is considerably more complex than the familiar lever escapement. The Omega iteration of the escapement is what Daniels has called the "extra flat co-axial escapement." As illustrated below, the extra-flat co-axial escape wheel does not carry a pinion to be driven by the fourth wheel (1). Instead, the fourth wheel drives a fifth half-oglive finger wheel (2), which in turn drives the upper escape wheel (3). The upper (3) and lower (4) escape wheel are fixed to a common shaft.
The pallet lever is indicated at (5). The pallet lever includes two jewels (6 and 7) which serve only to alternately lock the lower escape wheel. The third jewel on the pallet (8) serves only to receive an impulse from the fingers of the upper escape wheel (9). The impulse from the escape wheel is delivered to the balance wheel in two ways. On the clockwise swing, a tooth of the lower escape wheel (10) impulses the long jewel on the balance roller (inset A). On the counterclockwise swing, the upper escape wheel impulses the jewel (8) and the pallet fork (11) impulses the upright jewel on the balance (inset B) just as in a standard lever escapement. The lower balance shock assembly is indicated at (12).
The escapement is shown right with the balance rotating in the counterclockwise direction. The balance impulse jewel hits the lever fork and begins rotating the lever clockwise. The exit pallet (not visible below left) thus releases the escape wheel, which then impulses the center jewel (1) and the balance via the lever fork. The entry pallet then locks the escape wheel (2).
With clockwise rotation of the balance wheel, the lever is moved to the position shown at left in blue. The entry pallet is unlocked (1) and the escape wheel begins rotating. The lower escape wheel impulses the balance directly (not shown), and the exit pallet then locks the escape wheel (2).
The basic principles of the co-axial escapement are: (1) The exit and entry pallets serve only locking functions. (2) The center pallet serves only to impulse the balance in one direction (counterclockwise in the Omega implementation). (3) In the other direction, the balance is impulsed directly by the large escape wheel (clockwise in the Omega). (4) The small escape wheel serves only to impulse the center jewel. In the "extra-flat" design, the small escape wheel also serves as the component driven by the wheel train.
The balance is shown inverted (left). The lever fork lies on top of the impulse roller (1) with the balance installed in the movement, and the safety roller (2) is between the impulse roller and the balance. (This "inverted" design is probably a result of Omega using a mirror image of the original Daniels' design, which required inverting the pallet fork.) When the balance is impulsed by the lever, the upright jewel (3) is engaged. When impulsed directly by a tooth of the lower escape wheel, the "pallet" jewel (4) is engaged.
At left, we see the two sources of impulse for the balance. These are the inverted lever fork (1) and a lower escape wheel tooth (2). The lower balance pivot jewel is shown at (3).
Because the balance is free-sprung (without a curb pin regulator), a pair of opposing screws is used to adjust rate (left). A one-half rotation of both screws adjusts rate by approximately 30 seconds per day. Although this arrangement (similar to that used by Rolex) is hugely preferable to to a regulator construction, such simple screws lack the refinement, as well as ease and precision of adjustment of the Patek Philippe Gyromax with its rotatable collets. The Omega arrangement is, however, serviceable and functions adequately, if not conveniently. Unlike the Gyromax or Rolex balances (which, respectively, use six or eight and four weights), the paired screws of the Omega cannot be used to correct poise errors.
RETURN TO PART 2 OF THE ARTICLE CONTINUE TO PART 4 OF THE ARTICLE
