What’s the Mt. Everest of watchmaking? Is it a minute repeater? How about an ultra-thin caliber? Each requires special manufacturing know-how. Neither tolerates imprecision, and assembling either one requires tremendous skill. Now imagine an ultra-thin minute repeater. That’s a challenge the craftsmen at Vacheron Constantin accept every day. They are making the Patrimony Contemporaine Calibre 1731. In this feature we explain how Vacheron Constantin makes the world’s thinnest minute repeater.
Named for the year of Jean-Marc Vacheron’s birth, the Calibre 1731 features the thinnest minute repeater caliber available (3.9 mm) inside the thinnest minute repeater wristwatch on the market (8.09 mm). To put that in perspective, Calibre 1731’s case is thinner than many currently available manual-wind minute repeater movements.
Vacheron embarked on this project in 2009 with the goal of developing a new chiming caliber that meets the Geneva Seal standards. Those standards govern, among other things, timekeeping accuracy, movement design and construction, finishes and methods for applying them, and final product testing. The decision to make the new caliber ultra-thin came naturally, as Vacheron has been creating slim repeating watches for 175 years. In 1838, the brand produced a ladies’ quarter-repeating pendant watch with a movement measuring only 4.1 mm thick. The company’s first ultra-thin minute repeater for the wrist, Reference 4261, was produced in 1943. Its movement was a mere 3.28 mm thick. In 1992, Vacheron launched Reference 30010, with Caliber 1755. This movement, inspired by the 1943 model, also measured 3.28 mm thick. Calibre 1731’s slimming program began on the drawing board. Of course, many of the movement’s components had to be made thinner than in a traditional movement. The minute repeater complication was integrated into the movement, not located on a separate plate. To conserve space, the movement was designed with a single mainspring barrel, though the power reserve remains a very respectable 65 hours.
Once the design was complete, it was time to start making parts. Given the Geneva Seal requirements, movement finishes received great attention, and the minute repeater’s hammers presented an excellent opportunity to showcase Vacheron Constantin’s black polishing skill. Black polish, also called specular or mirror polish, owes its name to the laws of physics. A steel surface that is not perfectly flat produces a diffuse or scattered reflection, so it appears silver or gray when viewed from any angle. A black-polished surface, on the other hand, is perfectly flat. As a result, it reflects light in only a single direction. If a black-polished surface is illuminated from a single point, it will appear black from every direction, except that at which light is reflected. Parts with this finish act like mirrors inside the movement, reflecting the components around them in a kaleidoscopic manner. Achieving a mirror polish by hand is an art. An old joke has a young apprentice asking his master how to achieve a beautiful, flat surface with his file. The master replies, “It’s simple. First hold the file like this, then practice for 10 years.”
Creating a black polish finish is a multi-step process. The first phase is known as rubbing down. In the highest quality movements, such as the Caliber 1731, this is done by hand, using files. It can also be done with electronic assistance from buffs or burnishers, or mechanically, using a lapping machine. With a lapping machine, the components being finished, known as work pieces, are held in place and pressed against a rotating disk that is coated with a thin film of abrasive liquid or paste. This process is typically used for larger components with flat surfaces.
The final steps must also be done by hand. The finisseur prepares the working surface, usually a perfectly flat zinc plate. The plate and the work piece must be carefully cleaned to remove even microscopic impurities that might cause scratches. The finisseur applies a small amount of extremely fine diamond paste to the plate’s surface. The work piece is placed on the paste and moved slowly in small circles with a fingertip. The finisseur must apply precisely the right amount of pressure, distributed equally on the piece, to avoid creating high and low spots and to avoid any rounding. An expert can tell by feel when the grit has done its work. When it has, the component and working surface are thoroughly cleaned, and the process is repeated, using finer grits, until the perfect black finish is achieved. A single small component can take two days to finish. Each finished piece is examined by the department head, and any piece that does not pass muster is scrapped. Black polish is not only a beautiful tribute to hand craft, it also provides excellent protection against corrosion. Calibre 1731 has hand-chamfered bridges. Chamfering by hand involves removing material between the bridges’ surfaces and sides, typically with a series of very fine files, to create a 45-degree angle. The angle, or bevel, is then highly polished by hand with pegwood. This is a time-consuming process. Three types of angles can be created: exterior angles, rounded angles, and interior angles. The last of these is the most difficult to execute, typically requiring 18 months of experience to master.
Once completed, the hand-finished components are sent to the High Complications Workshop. This is where Vacheron Constantin’s most complex movements are assembled. Each movement is assembled from start to finish by one of three watchmakers – one master and two apprentices. Don’t let the “apprentice” title fool you. These watchmakers are the best of the best, and they have travelled for 15 years to reach this destination. Their journeys began with three or four years of formal training at watchmaking school. That training provides a solid foundation, yet significant additional experience is required to become a complete watchmaker. At Vacheron Constantin, newly graduated watchmakers usually begin their careers in the assembly workshop, constructing less complicated movements. They do this for five to eight years, gaining new knowledge, new skills, and a thorough understanding of Vacheron Constantin’s watchmaking techniques.
Those desiring to continue their training can move up the ladder to the adjusting, casing, or complications departments, where they spend several more years acquiring additional skills and knowledge. For those few with the desire and the aptitude, one final step remains – a coveted apprentice position in the High Complications Workshop. If they get there, the minute repeater will be their ultimate test. Assembling a minute repeater caliber presents several unique challenges. In this workshop, each watchmaker must possess not only good eyes and steady hands, but also an excellent ear. Vacheron says it can take from three to six months to assemble a minute repeater caliber, and a significant portion of that time is devoted to perfecting the sound.
Minute repeaters typically have two hammers and two gongs, one set producing the low tone, and the other the high tone. The low tone indicates the hours; high and low tones in quick succession indicate the quarter hours; and the high tone represents the minutes. Each tone must be strong and clear, and the two frequencies together must produce perfect harmony. The sound is produced when the hammers strike the gongs. The hammers are different sizes and weights, each matched to the gong it will strike. The hammers must strike the gongs in just the right position, and with precisely the right amount of force – enough to generate a powerful tone, but not so much as to overpower the gong. That means the spring that powers the hammers must be adjusted to deliver just the right amount of energy.
The hammers must also be adjusted to strike with the proper speed or cadence. Springs do not deliver power at a constant rate: they deliver more at full wind and less as they wind down. In a minute repeater, that can lead to the hammers striking too fast early in the chime and too slowly at the end. Ideally, the strikes are equally spaced throughout the chime. To address this problem, Vacheron has developed a patented silent strike governor. Activating the repeater starts the governor spinning, creating a centrifugal force. That causes one end of the fly-governor weights to pivot out while the other end pivots inward, acting as a brake on the governor’s central shaft. This regulates the energy flow so the hammers strike with an even cadence. Vacheron’s watchmakers test the system by timing the hammer strikes at 4:49. That chime consists of four hour strikes, three quarter-hour strikes, and four minute strikes. The four hour strikes at the beginning of the chime should take the same amount of time as the four minute strikes at the end. If they don’t, additional adjustments are made until the cadence is right. The governor also offers another benefit: it operates silently, so instead of the whirring sound some repeaters produce, the owner hears only the pure tones the watchmakers work so hard to achieve.
Once the hammers are adjusted for both power and speed, the watchmaker turns his attention to the gongs, and the real fun begins. Each gong is a round wire precisely shaped to wrap around the movement. The gongs are joined to a foot that attaches to the movement. The watchmaker installs the gongs and lets the hammers strike. If the tone is not just right, the watchmaker removes the gongs and uses a fine file to remove a tiny amount of material from the gong, near the foot. The watchmaker must exercise great care not to remove too much material, for doing so ruins the gong. The watchmaker may also bend the gongs very slightly. This five-step “remove-file-bend-reinstall-test” process is repeated, again and again, until the tones are just right.
How do the watchmakers determine when the tone is just right? It’s not done with electronic frequency analyzers. Remember, this is old-world hand craft, and each master watchmaker has his own personal approach. One watchmaker has created an unusual metal mount to which he attaches the gongs. He holds the mount between his teeth and strikes the gongs, allowing him to both hear and feel the resonance. Another watchmaker uses his left ear only, not his right. He holds the gongs close to that ear and plucks them like guitar strings to assess the quality of the tone. For these watchmakers, assembling a minute repeater is a highly personal undertaking. Once everything is adjusted and the sound is just right, the watchmaker who assembled the movement submits it to the other two watchmakers for their review. Each watchmaker spends months assembling individual movements from A to Z, but all three watchmakers must approve each movement before it is placed in its case. Of course if you have a great orchestra, you want it to play in a great auditorium. The same is true with minute repeaters, and the watch case is the concert hall. To maximize the movement’s audible output, the gongs are attached directly to the movement’s mainplate, which is in turn fitted to the case very precisely so that the sound from the gongs is transmitted to the case. This fitting requires small modifications to each movement to assure a perfect fit.
The case is constructed in a way that maximizes the transmission of sound. Rather than use a snap-fit bezel or small screws to attach the caseback, Vacheron designed those components with threads so they screw into the case, improving the propagation of sound. As we’ve seen, assembling a minute repeater involves so many hand-executed customizations that each watch becomes a unique piece. Neither the gongs nor the movements can be interchanged with those in other watches. For this reason, no two minute repeaters sound precisely the same, and to the dismay of some owners, the sound of a minute repeater’s chime can change over time. To alleviate that concern, Vacheron Constantin will record the sound of each completed Calibre 1731 in a soundproof box. The recording will be kept in the company archives, to be consulted when the watch is serviced. The watchmakers will use the recording to assure that when the watch leaves, it sounds just as it did when it was new. In an ideal minute repeater, aesthetics complement harmonics. Vacheron Constantin’s Patrimony Contemporaine family is defined by slim and classically understated timepieces, and the Calibre 1731 fits right in. The new model measures 41 mm by 8.09 mm and it incorporates several Patrimony Contemporaine design features, including a thin, curved, polished bezel, a large dial opening, baton hands, a convex dial with triangle and baton hour markers, and a “pearl” (small dots) minutes track. The dial was inspired by Vacheron’s Reference 6179, produced during the 1950s. The case is 18k 5N rose gold and has a sapphire back.
Vacheron Constantin had two design objectives for this watch: to make a case whose understated, elegant lines would match the purity of the chimes, and to hide the complex movement within a discreet exterior. Some collectors call this “stealth.” Indeed, even a knowledgeable enthusiast might need a moment to discern that this watch is more complicated than it first appears. The small seconds at 8, rather than 6, hints that this watch is different. The slide on the side of the case confirms that it belongs to the elite club of minute repeaters. Vacheron says it knew the design was just right when it reached a perfect balance – nothing could be added, and nothing taken away. The first Calibre 1731 was delivered in January 2014. Each piece is accompanied by a special box with a “La Musique du Temps” resonator that enhances the chimes for the owner’s listening pleasure. The watch is priced at $369,300.
This article appeared in the December 2013 issue of WatchTime Magazine.