Monday, March 16, 2015

Vacheron Constantin - Coffret Observatoire, a Unique Atelier Cabinotiers set of five watches

Prestigious Swiss watch manufactory Vacheron Constantin has recently unveiled a unique Atelier Cabinotiers set composed of five masterpieces of watchmaking, Tourbillon pocket watches, in the spirit of the Observatory pieces made in the early 20thcentury. This one and only set was purchased by a fine collector, who bought the privilege of owning the accumulated know-how in the Observatory field. An extraordinary and completely unique set of five watches, each watch being singularly unique, each watch made with an individual very special high-precision movement of the highest technical significance, together demonstrating the breathtaking technical accomplishment of Vacheron Constantin.

•Tourbillon with detent Chronometer escapement
•Tourbillon Constant force escapement
•Tourbillon «Remontoir d’Egalité»
•Tourbillon Marine Chronometer balance

Created in 2006, Vacheron Constantin’s Atelier Cabinotiers revives the very unique spirit of 18th century. At that time, prestigious clients came to order directly from the cabinotiers, the watchmakers and craftsmen who forged the city’s reputation. Atelier Cabinotiers offers a wide range of service going from a unique dial to a complete creation of a timepiece that implies the development of the caliber to the design of the case.

When a watch is being used by the wearer, it is, quite naturally, moved in many different positions during the course of that period – such as upside down, upright, flat and sideways. Even today, one of the greatest challenges for a watchmaker is to regulate a watch for consistent accuracy no matter what position it is in. The mechanism known as a “tourbillon” provides an extremely effective solution to this obstacle. In a standard watch movement with a fixed escapement but without tourbillon, the timekeeping ability of the watch can be affected by changes in the position of the watch because the effect of gravity “pulls” down on the oscillating balance wheel and hairspring creating very small distortions which therefore affect accuracy of timekeeping, this effect is known by watchmakers as “positional error”.
The tourbillon is essentially a revolving platform and “cage” upon which the whole escapement is mounted that makes one full rotation in one minute. It was invented specifically to improve the timekeeping of pocket watches that were usually kept upright (vertically) in the wearer’s pocket and therefore were most subject to the effects of gravity. The tourbillon very successfully equalizes these gravitational errors by turning the balance on its own axis in all possible vertical positions during the course of each 60-second rotation. In other words, because the balance wheel and escapement are kept constantly rotating and not fixed in any one position the effect of the gravitational pull is regularized and equal and the watch can therefore be regulated to keep time unaffected by any random change in position during use. The tourbillon has always been one of the most challenging watch mechanisms to make, requiring the most skillful craftsmanship in its manufacture to create not only a mechanism with an important technical purpose but also an object of visual intrigue and beauty. The movement of the present watch is an historic vintage tourbillon by Vacheron Constantin which has been made and improved upon to exceptional modern standards to form part of this unique and extraordinary set of watches.

Tourbillon with detent Chronometer escapement
This exceptional watch by Vacheron Constantin can, along with the other four watches in this unique set, be considered a masterpiece of watchmaking and one of very few watches known with both tourbillon and detent chronometer escapement.

The escapement of a watch is the part that “ticks”, it is a mechanism which allows the power from the mainspring via the wheel train to be released and therefore the hands to advance in the correct small increments to indicate the passage of time. The escapement incorporates the oscillating balance wheel with hairspring that can be seen turning backwards and forwards in the movement of any mechanical watch.
As with most watchmaking innovations over the centuries, the development of the watch escapement was mainly concerned with achieving accurate precision timekeeping. For the majority of watches the most widely used and consistently reliable escapement is the “anchor” or “lever” which has been predominant since the middle of the 19th century. However, where extreme accuracy is required, for instance in watches used for navigation or observatory calculations, a more sophisticated and intricate escapement called a “detent chronometer” is used and in the present watch it is combined with a tourbillon – an extremely rare and unusual combination requiring immense skill to construct and resulting in a watch that could be used for the most exacting of timing purposes.

The difference between the detent chronometer and the standard anchor escapement is that the chronometer escapement, being unidirectional, has no recoil during its action whereas for each motion of the standard anchor escapement there is a very slight backward motion or recoil because the two pallets of the anchor are alternately engaged on both the forward and backward swing of the balance. The elimination of the recoil in the detent chronometer provided by its unidirectional action and almost detached balance makes it much more precise and capable of extreme accuracy.

A watch with detent chronometer escapement can be visually recognized by looking at the action of the small seconds hand which moves in a noticeably precise way in half-second “jumps” as opposed to the typical “sweeping” action of a watch with anchor escapement. The detent chronometer escapement works by the controlled locking and unlocking of the ruby pallets that provide the impulse to the escape wheel, a long thin straight spring or “detent” momentarily locking the escape wheel by its teeth until it is released again on each forward swing of the balance, the ruby pallet mounted on its staff unlocking the escape wheel as it passes and allowing it to advance by one tooth at a time. The balance wheel of the detent chronometer swings almost free and undisturbed by the escapement resulting in very little friction between the components, again contributing to the overall accuracy of the watch.

Tourbillon Constant Force Escapment
The constant force escapement has a very sophisticated additional mechanism attached to the escape wheel of the watch’s movement which as the name implies, supplies a constant, equal and unchanging power charge to the lever escapement throughout the entire running period of the watch. Whilst the escapement itself is driven and powered by the mainspring via the tourbillon in the usual manner, the integral constant force mechanism discharges the power at precise intervals so that the timekeeping of the watch is unaffected by the changes in the force of the mainspring as it runs down. This means that this ingenious mechanism allows the watch to run at a constant unfluctuating rate regardless of whether the watch is fully wound or running down.
The constant force mechanism of this uniquely constructed Vacheron Constantin watch comprises a spiral spring mounted directly above the escape wheel on its arbor which is wound and released at very short intervals by two further toothed wheels mounted below with which a jeweled lever locks and releases the spring above. Therefore each time the spiral spring is wound and released a small “charge” of power acts upon the escape wheel so that it is always powered at exactly the same moment and with an unchanging amount of energy at all times and as such can never be affected by any fluctuation during the mainspring’s running cycle. The constant force escapement is extremely rare in any watch and this exceptional watch has been made to a unique design by master watchmakers. Not only does it contain a unique constant force escapement but this is coupled with the tourbillon mechanism, altogether a great achievement of haute horology.

Tourbillon «Remontoir d’Egalité»
For a watch to run accurately it could be said to have two separate but integral “halves”; one half to provide the power to run the watch (the mainspring andwheels) and the other the escapement which releases that power at exact and precisely calculated intervals. The mechanism known as “remontoir d’égalité” can be thought of as a bridge between these two halves because it regularizes the supply of power and at the same time directly controls the running of the escapement. The “remontoir d’égalité” is essentially a very high-precision power transmission control mechanism to combat even the most minor negative effects on accuracy caused when the mainspring is winding down so that the accuracy of the watch is maintained and unaffected by the fluctuations in power during the entire period of running.

The “remontoir d’égalité” also corrects any possible variation in accuracy that could be caused by the mechanical action of the wheels themselves in the train between the mainspring and tourbillon. In short, the “remontoir d’égalité” compensates for any small potential error caused simply by the normal running and unwinding of a mechanical watch in the parts of the watch up to, but not including, the escapement which has its own compensatory devices. The “remontoir” achieves this by loading and releasing stored power from an extra spring on the tourbillion that is released in exactly controlled amounts, in this watch, at 10 second intervals, therefore equalizing exactly and constantly the power from the mainspring to the tourbillion.
In this exceptional and unique Vacheron Constantin watch, the “remontoir d’égalité” is used in combination with the tourbillion – to combat errors due to the change in the watch’s position and a balance wheel and spring that have been made to correct fluctuations in temperature. As such, this watch has compensation devices to combat errors in power transmission, position and temperature so as a result is capable of extreme accuracy. The “remontoir d’égalité” is almost never seen in a portable watch because of the high level of skill required to make it. Only the very best watchmakers are capable of constructing a watch with this complication because if a watch has a “remontoir d’égalité” it means that the entire watch has been specially designed and made specifically to allow for its inclusion meaning that the entire layout of the wheels of this watch is different to that of other tourbillion watches and can therefore only ever be hand-made as an individual piece.

Tourbillon Marine Chronometer balance
Change in temperature has one of the greatest negative effects on the accuracy of a watch by causing the metal to expand or contract. When the hairspring and balance expand and contract it naturally causes slight changes in the diameter and elasticity of the components and this in turn makes the watch go faster or slower. Technically speaking, it is in fact the balance spring or hairspring which is affected and during extreme changes in temperature this can cause a watch to lose or gain as much as four seconds per day. To counteract this problem, the balance wheel of the watch is specially made to compensate for these expansions and contractions. The unique balance wheel of this watch is made to allow fine adjustment to compensate for the errors in timekeeping that can be caused by fluctuations in temperature. The design is taken from the principle of the marine chronometer balance, the marine chronometer being an instrument of high-precision for navigational purposes.
The visibly distinctive and very special feature of this balance is the four large gold weights mounted on the rim of the balance in addition to twelve screws for extra-fine adjustment. The balance wheel itself is bimetallic, made of two strips of metal with different rates of expansion and open free ends to allow movement during temperature fluctuation, the four large gold weights are then placed on the rim of the balance during adjustment and testing of the watch by the watchmaker until they are situated in the optimum position to counteract the contractions and expansions of the balance rim. Put simply, the bimetallic balance and special compensation weights mean that the oscillation of the balance remains the same in any normal range of temperatures and therefore the accuracy of the watch is almost unaffected.

In this unique watch by Vacheron Constantin, the special balance for temperature compensation is combined with the tourbillon mechanism for the correction of positional errors. The marine chronometer-type balance is very rarely found in a watch due to the skill required to both construct it and regulate it for use and almost never used in combination with the tourbillon. This watch is further testament to the excellence of workmanship of Vacheron Constantin.

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