DETENT ESCAPEMENT
FABRICATION OF A DETENT ESCAPE WHEEL, THE ARTISANAL METHOD
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The detent escapement is a detached escapement with direct impulse, historically used in marine chronometers. Unlike other escapements, it is characterised by delivering only one impulse per oscillation to the balance, thus referred to as a single-beat escapement.
The invention of the detent escapement is attributed to Pierre Le Roy around 1748. During the 18th century, its development was refined by Thomas Earnshaw and John Arnold. These watchmakers were driven by the pursuit of precision dictated by the demands of maritime navigation, at a time when the accurate determination of longitude was a critical strategic advantage.
The detent escapement quickly became the preferred choice for marine chronometers due to its minimal interference with the balance. Used until the early 20th century, it is now rare in contemporary watchmaking, although some modern artisans still employ it in exceptional timepieces.
The operation of the detent escapement is based on the principle that the escape wheel delivers only one impulse per oscillation. The detent serves to lock and release the escape wheel precisely. The impulse is given directly by the escape wheel to the balance. No friction occurs between the escape wheel and the balance during the free oscillations, thereby maximising the isochronism of the system.
The key components are:
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The escape wheel, featuring sharp, widely spaced teeth, typically made of gold.
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The detent, which releases the wheel at the appropriate moment to allow it to deliver its impulse to the balance.
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The detent spring, usually a fine blade made of steel or gold, acts as the locking element.
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The roller, fitted directly to the balance staff, which carries the unlocking and impulse jewels.
The detent escapement offers the best possible chronometric performance. However, its construction makes it highly sensitive to shocks, and its use in a wristwatch requires additional security measures to prevent the risk of overbanking. To date, only a few wristwatches have been produced with such an escapement.
Advantages
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High chronometric precision: The complete absence of friction during the supplementary arc of the balance wheel promotes excellent isochronism.
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Direct impulse: Energy is transmitted more efficiently than with a Swiss lever escapement.
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Unhindered balance motion: The balance oscillates freely through most of its cycle, reducing mechanical disturbances.
Disadvantages
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Extremely shock-sensitive: a fall or jolt may cause the unexpected overbanking or jump of the mechanism, making the escapement unreliable during active wear.
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Complex to manufacture and regulate: assembly and fine adjustment require rare expertise, limiting its use to very high-end or experimental timepieces.
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Poor adaptability to wristwatches: due to its sensitivity, it is unsuitable for everyday wristwatches and remains reserved for fixed instruments (such as marine chronometers) or collector’s pieces.