Technical point of view of stopping the tourbillon Set the tourbillon with second-level accuracy.
The tourbillon is generally considered to be one of the most prestigious complications, and it is also a manifestation of the skill and craftsmanship of the watchmaker capable of creating this fascinating mechanism. Invented by Breguet in 1801, its purpose is to eliminate the influence of gravity on the watch adjustment mechanism. The change in position has a significant impact on the way the watch travels. In the tourbillon, a moving bracket that rotates at a low speed (usually once per minute) is equipped with a balance wheel, hairspring, and escapement to average the position error. Therefore, tourbillon watches are designed to time time with superior accuracy, but until recently they had a major flaw. It is impossible to set the time in a second-accurate manner using the classic stop-seconds function. In fact, it seems logical and obvious to be able to synchronize movement with time signals.
The ability to stop the balance wheel and the second hand of the mechanical movement is crucial. Traditionally, pulling the crown of the watch through the dial mechanism causes the brake to contact the edge of the balance wheel and stop it. When the crown is pushed back, the brake is released, and the balance wheel and the second hand immediately restart. But stopping the balance in the tourbillon is not simple, because the balance swings in a rotating frame. The brake may hit one of the cage struts, rendering it unable to perform its function. Stopping the cage itself is not the solution. The balance will remain free to oscillate, and will eventually slow down, lose its amplitude, and stop, which is considered unsatisfactory (at least for some people). The escapement is also at risk of damage.
The first watch to provide a solution was the Lange & Söhne Cabaret Tourbillon in 2008 (relaunched in 2021). Lange’s solution included designing a very special brake spring. The V-shaped part (reminiscent of a mustache) is articulated, so if one of the two arms comes into contact with one of the struts, the other will still advance to the rim of the balance wheel and perform its function. Its geometry ensures optimal function under all conditions. In 2014, with the introduction of the 1815 tourbillon, the German manufacturer went one step further and added a zero-return function, thanks to the heart-shaped cam mechanism that resets the second hand when the crown is pulled.
Several brands followed in Lange’s footsteps and each provided its own solutions to the problems. Another German manufacturer, Moritz Grossmann, has proposed brands that are committed to stopping the rim of the balance wheel without hitting one of the pillars with original and poetic solutions. The beautiful Bennu Tourbillon was launched in 2014, with a three-minute flying tourbillon in a large 16 mm frame. The brake used to stop the balance consists of a tiny rotating brush made of human hair (visible here near the 25-minute mark). The cage posts pass through the hair, but they are hard enough to prevent balance.
IWC hacking Tourbillon was launched in 2017 and uses two levers to clamp the rim of the balance wheel like pliers. Each lever has its own spring, and if one lever hits the pillar, the other will stop balancing. This system has been applied to many tourbillons of the brand, such as the Da Vinci Tourbillon Retrograde Chronograph, the Portuguese Tourbillon Retrograde Chronograph or the Portofino Manual Winding Tourbillon Retrograde Chronograph.
In order to set their parallax tourbillon most precisely, the Gronefeld brothers decided to stop the frame (and reset the second one), thanks to the pin under the bracket. Its push-wind/push-setting crown allows switching between the two modes. When switching to the setting mode, a lever is moved. The movement continues to run, but once the cage pin engages the lever, the movement stops. In short, the flying tourbillon and the central seconds hand continue to rotate synchronously until they reach the 12 o’clock position and stop.
Montblanc Exo-Tourbillon is an original tourbillon architecture that provides another solution. Its balance wheel swings on a higher plane outside the cage. Therefore, it can realize the traditional and simple stop-second mechanism and block the balance wheel by the brake.
German independent watchmaker Karsten Frassdorf obtained a patent in the Ei8ht Tourbillon and implemented a new, efficient and elegant solution for applying the stop-second mechanism to the tourbillon movement. Instead of stopping the balance wheel in the traditional way, Frassdorf allows the brake to be in horizontal contact with the rim of the balance wheel. Instead, the balance wheel is stopped vertically with a double roller (now a dual-function roller). In addition to improving braking efficiency, there is naturally no risk of hitting one of the pillars of the tourbillon frame.