Complication · Precision
Constant-Force Remontoire
Partially verifiedA supplementary mechanism, interposed between the mainspring and the escapement, that periodically rewinds a small local spring or weight so the escapement always receives an almost constant driving force, independent of the mainspring's varying torque as it unwinds.
Definition
A supplementary mechanism, interposed between the mainspring and the escapement, that periodically rewinds a small local spring or weight so the escapement always receives an almost constant driving force, independent of the mainspring's varying torque as it unwinds.
Historical origin
Remontoire mechanisms were developed from the eighteenth century for precision timekeepers, notably marine chronometers and astronomical regulators, where the varying torque delivered by a mainspring or weight as it runs down was recognised as a significant source of rate variation; John Harrison's and later chronometer makers' work is frequently cited in horological literature discussing early remontoire designs, though attribution for specific forms varies between sources.
How it works
A remontoire is typically a small secondary spring (or, in some clocks, a small weight) that is rewound at short, regular intervals — commonly once every 30 or 60 seconds, or once per minute — by the main going train, and which in turn drives the escapement directly.
Because the remontoire spring is only ever wound through a very small, consistent arc before being released again, the torque it delivers to the escapement varies far less than the torque a mainspring delivers across its entire multi-day unwinding, giving the escapement a much more uniform impulse regardless of the mainspring's overall state of wind.
The rewinding action itself must be arranged so that it does not disturb the escapement's own impulse — commonly achieved by having the rewind occur through a separate gathering pallet or a brief moment when the escapement is between impulses — since a remontoire that visibly disturbs the going train at each rewind would defeat its own purpose.
Pocket watch context
Found in a small number of very high-grade precision pocket watches and chronometer-style pocket watches aimed at scientific or observatory-standard timekeeping, where the added complexity was justified by measurable rate improvement rather than by display value.
Wristwatch context
A specialist, high-cost modern wristwatch complication, generally marketed explicitly around its rate-stability benefit; because a wristwatch's mainspring barrel is small relative to a marine chronometer's, the practical rate benefit and the engineering challenge of fitting a remontoire in a wristwatch-sized movement are both significant.
Clock context
Long associated with precision pendulum regulators and astronomical clocks, and with marine chronometers, where a gravity or spring remontoire rewound at short intervals was a recognised route to improving rate stability beyond what a fusee alone could achieve.
Identification
- A visibly separate small spring, weight or lever assembly positioned between the barrel/fusee and the escapement, distinct from the main mainspring barrel
- Movement may show a small secondary 'tick' or step in the remontoire's own release, visually or audibly distinct from the escapement's beat
- Should not be confused with a fusee, which equalises torque across the mainspring's full run but does not periodically rewind a separate local spring
Servicing notes
Remontoire mechanisms are mechanically delicate and calibre-specific; incorrect timing of the rewind relative to the escapement's impulse can degrade rather than improve rate, so adjustment and repair require a watchmaker or clockmaker experienced specifically with remontoire and precision-escapement work.
General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.
Related photographs
No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.
Sources & references
- Rawlings, A. L., The Science of Clocks and Watches
- Attribution of specific early remontoire designs to individual makers varies between secondary sources and was not independently resolved here.
Where sources disagree, the disagreement is stated rather than resolved silently.