In a mechanical watch, it all starts with a mainspring housed in the barrel. It relaxes, feeds a train of gears... and would go, without constraint, to the unleashing. The escapement then intervenes like a conductor: it delivers energy in small, regular bursts and keeps the balance spring oscillating. It is the point of contact, the fragile meeting between brute force and measurement of time. And it is this dry noise, this ticking, which reminds us that here, the second is a repeated victory.
The most widespread today, the Swiss lever escapement, is made up of three main players: the escape wheel, the lever and the balance spring. The wheel, with its sharp teeth, pushes. The anchor, capped with two stones (the entry and exit paddles), locks then releases. The balance wheel, equipped with a hairspring, oscillates and, via a small ellipse fixed on its plate, controls the anchor. Between them, a precise ballet of impulses, locks and rests.
This game of clutches and slips is repeated thousands of times per hour. At 4 Hz (28,800 vibrations/hour), the escapement delivers eight pulses per second. The regularity of this cycle, the famous isochrony, provides precision.
The frequency, expressed in Hz or in vibrations/hour, indicates the number of oscillations of the balance wheel. 3 Hz (21,600 vph) or 4 Hz (28,800 vph) have become standards, 5 Hz (36,000 vph) remains the prerogative of sporting or historical calibers. The amplitude (often 270° to 310° at full winding) measures the angle of oscillation. Too weak, it betrays friction or a lack of energy; too high, it can cause flapping. Finally, isochronism is the ability of the balance spring to keep the same period whatever the angle and the residual force of the spring. It owes as much to the design of the balance spring (surprise: the Breguet-type terminal curve plays a role) as to the purity of the escapement impulse.
In a Swiss lever escapement, the impulse faces of the vanes and teeth of the wheel work in sliding friction. Rubies (or synthetic sapphires) reduce wear, and a micro-drop of oil, dosed at the ankle, ensures regular gliding. But the oil ages: it thickens, disperses, alters the pace. This is why so many innovations aim to reduce lubricated surfaces or to substitute low-friction materials.
In 1974, George Daniels imagined the Co-Axial escapement: a geometry which transforms part of the sliding into rolling. Result: less lubrication on the pallets, a “purer” impulse transmitted to the balance wheel, and increased chronometric stability over time. Marketed by Omega from 1999, it set a precedent, proving that it was possible to modernize the lever without denying watchmaking aesthetics.
Rolex has redesigned the Swiss lever with its Chronergy: a paramagnetic nickel-phosphorus escape wheel and reworked angles for a gain in efficiency measured around 15%. Patek Philippe, with Pulsomax, has pushed the logic of silicon to the anchor and the wheel, combining lightness, hardness and absence of lubrication. Ulysse Nardin dared direct impulse with the Silicon Dual Direct Escapement in 2001, when Girard-Perregaux explored constant-force with its Constant Escapement. So many contemporary ways to answer the same question: how to give the pendulum a regular, clean, lasting impulse.
The history of the exhaust is an epic. The verge of pocket watches, crude but founding; the anchor of clocks (17th century) which tames the pendulum; then Thomas Mudge, in 1755, who invented the lever escapement, ancestor of the modern Swiss lever. In the 19th century, industrialization refined angles, standardized stones, and codified “lift angles”. In the 20th century, we tracked losses, we understood the “pull” which ensures the return of the anchor against the stop, we improved safety against shocks. And at the end of the century, Daniels reinvented the impulse. The escapement is like this: an ancient art, constantly renewed.
The ticking is not just a sound charm. It tells of the symmetry of movement. A tick more marked than the tock? This may be a “beat error”: the ellipse is not perfectly centered in relation to the stops, and the balance wheel does not spend as much time on either side of zero. On a chronocomparator, we then read the equality of the beats, the amplitude, the walking rate. The health of an exhaust depends as much on its geometry as on its cleanliness - a dry oil can be guessed by the noise, a poorly absorbed shock on the diagram.
On the scale of a watch, the escapement is a renewed handshake between energy and time. A tiny gesture, repeated millions of times, which gives mechanics its humanity: the imperfect but faithful cadence of a beating heart.
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