For a moment put yourself into the shoes of a horological engineer tasked with building the most precise mechanical timekeeper possible. What features would you need to include to see the highest level of performance? Marine chronometers are a great starting point as their precision was responsible for navigating ships across oceans before the advent of the satellite-based global positioning system. A gain or loss of just 4 seconds meant a navigational error of 1 nautical mile. In many cases the precision of marine chronometers was the difference between successfully crossing an ocean, or being lost at sea. Precision chronometry is often overlooked in modern watchmaking in favor of aesthetics or brand ambassadors. But there is one watchmaker who has made the pursuit of chronometry his life's work. His name is Karsten Fra?ssdorf, his brand is Montres KF, and his new Spirograph Sport watch is a chronometric masterpiece.
Montres KF Spirograph Sport tourbillon detail.
Fra?ssdorf started studying watchmaking when he was 15, as an apprentice to a local master watchmaker. He finished his apprenticeship in 1984, and entered the industry. Early in his career, Fra?ssdorf worked mainly on clocks. During this work, he discovered the deep technical aspects of the marine chronometer, which influenced his focus today on errors due to temperature. I asked Fra?ssdorf about this, and he said, "In my opinion, marine chronometers make normal wristwatches a bit boring."*
Karsten Fra?ssdorf.
Before looking at the Montres KF Spirograph Sport, let's dive deeper into marine chronometers. Two prominent features contribute to keeping marine chronometers so incredibly precise. First and foremost is their use of massive balance wheels. These balance wheels are both heavier and larger, compared to what we are normally see in wristwatches. Large adjustable weights on the balance wheel rim further increase the moment of inertia. The larger the moment of inertia of a balance wheel, the more stable its oscillations. Small shocks or bumps won't disturb it as much as they would if the moment of inertia were less. Second, the balance wheels we see on marine chronometers are usually split, as in not complete and solid circles. This type of balance is referred to as a compensation balance. The compensation balance is a sandwich of steel and brass, and it changes its diameter as temperature changes, to compensate for the temperature-induced changes in the elasticity of the steel balance springs then in use. As temperature increases, a watch with a plain steel balance spring will tend to lose time; a compensation balance's outer arms move inward as temperature increases, which tends to cause a gain in time, "compensating" for the change in elasticity of the balance. Such balances were found in marine chronometers but also in high grade pocket watches as well, until the invention of modern Nivarox-type alloys in the 1920s.
Marine chronometer by Frodsham, with compensation balance and helical blued steel balance spring.
Montres KF Spirograph Sport dial color variations.
As you can probably deduce at this point, the Montres KF Spirograph Sport has a compensating balance wheel. As far as I am aware, Montres KF is the only *brand producing watches today with actual compensating balance wheels. We sometimes do see split balance wheels in modern watches but their purpose is primarily aesthetic, as they contribute to an old-fashioned style. If there are others, I would be happy to be corrected. Instead of compensating balances in modern wristwatches, we instead see other chronometric mechanisms featured, like the tourbillon or constant-force devices. It makes sense, as these are easier to observe and understand.
So, why a compensating balance in a watch with a modern Nivarox balance spring? Although steel balance springs are no longer used, modern Nivarox-type balance springs and uncut Glucydur-type balance springs still show some residual temperature error. Modern balances expand as temperature increases, which slows the rate. This is compensated for by the balance spring, which unlike steel balance springs, tend to cause the watch to gain as temperature increases. Compensation, however, isn't always perfect and to allow the watchmaker to exactly adjust for the temperature error in a modern balance spring, and correct for it, Karsden Frasdorf has developed a new type of balance wheel, seen below.*
Detail of the Montres KF Spirograph Sport balance wheel.
The curved arms of the balance move in or out as temperature changes, and there are screws placed along the curved arms which allow the watchmaker to control the degree of compensation obtained from the balance. The bar at a right angle to the to the temperature compensation arms carries screws at each end. The "classification" screws are used to bring the balance to time, and the fine adjustment screws, to obtain fine adjustment of its rate.*The balance is made of non-magnetic steel, and the watch is equipped with a stop-seconds function (an unusual feature in a tourbillon wristwatch) which allows for more accurate time-setting, and which also allows you (if you wish) to stop the watch to view the unique balance design.
Think of the Montres KF Spirograph Sport as a marine chronometer on your wrist. The large balance oscillates at the classical rate of 18,000 vibrations per hour inside of a tourbillon cage rotating once per minute. The unusual shape of the balance wheel, with its large auxiliary compensation weights, is*intriguing to watch as it oscillates. The entire movement is mounted on shock absorbers, which can absorb up to 5,000 Gs, according to the brand. The power reserve is shortened on purpose (from a theoretical power reserve of 70 hours, to 44 hours) by using a Maltese cross mechanism, in order to ensure a more constant balance amplitude throughout the movement's autonomy. (Maltese cross stopworks can be found in many high-grade mechanical pocket watches, and were intended to restrict running time to the part of the mainspring's output that provided optimum balance amplitude) And even with the extreme focus on performance of the Spirograph Sport, the finishing is very nicely done.
Detail of the Montres KF Spirograph Sport tourbillon.
The case is 45mm, and both the dial and movement are decorated with a honeycomb motif. (Montres KF explains that the honeycomb motif is inspired by the coat-of-arms of La Chaux-de-Fonds, the Swiss city that is home to the brand.) In addition to its focus on the more technical aspects of watchmaking, the Spirograph Sport can be completely customized. The strap, case metal, dial colors and movement decoration are all left up to the personal choice of the owner. Since only 10 examples of the Spirograph Sport are being produced this high level of customization is realistic.
Montres KF Spirograph Sport assembly, showing the compensating balance and tourbillon cage.
The hairsprings in the Spirograph Sport are hand-formed, with an inner Grossman curve and outer Phillips terminal curve (an overcoil; both curves are designed to allow the balance spring to "breathe" more concentrically). Fra?ssdorf does thermal and shock testing himself, but is planning to get official observatory certifications soon. The challenge with this is the small number of movements Fra?ssdorf completes every year. Sending just one movement to an observatory for an extended testing period would represent a significant percentage of his work.
Detail of the Montres KF Spirograph Sport balance, showing the compensation movement in red.
Today, we spend a lot of time thinking about how a watch looks. The style of the case is important, the look of the dial is crucial, and the finishing of the movement is important. At the same time we are losing touch with a very important aspect of any wristwatch, which is how well does it keep time? With Montres KF, Fra?ssdorf brings a refreshing perspective on chronometry to watchmaking.
Bringing a balance to time with a reference balance.
The Karsten Fräsdorf Spirograph Sport: case, 45mm x 13.6mm stainless steel, honeycomb dial motif. Water resistance, 50 meters. Movement, KF caliber 440, in-house one minute tourbillon with compensating affix balance; shock-resistant suspension tested to 5000 Gs; 70 hour theoretical power reserve restricted to 44 hours by Maltese cross stopworks. Price, CHF 95,000. Find out more at Montres-KF.com.


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