In December of 2018, Andreas Strehler lectured at the Horological Society of New York, and while he was here I got a chance to to take a close look at his new Trans-Axial Tourbillon. This is watch full of surprises, both technical and artistic. Seeing the watch in person gave me a new appreciation for remontoir devices, and gave me the opportunity to speak with Strehler directly about the research and development that went into this phenomenal timepiece.
After graduating from watchmaking school in Switzerland, Strehler got his start working at the legendary complications specialist Renaud & Papi (today Audemars Piguet Renaud & Papi), alongside Robert Greubel, Stephen Forsey, Bart and Tim Grönefeld, and Peter Speake-Marin. After his experience at Renaud & Papi, Strehler established his own workshop to begin development of both his own watches, and to start as a freelance horological engineer and manufacturer. Today, Strehler's company, UhrTeil AG, works behind the scenes for many famous watch brands (H. Moser & Cie., Harry Winston and Maurice Lacroix to name just a few), focusing on specialized movement production. Additionally, Strehler is a Prix Gaïa laureate and a member of the Académie Horlogère des Créateurs Indépendants (AHCI).
Before looking at Strehler's Trans-Axial Tourbillon, it makes sense to discuss some of the basics of remontoir devices. In mechanical watches, the mainspring acts as the power source. The tightly coiled mainspring is wound through the crown, or through an automatic winding rotor. As the mainspring uncoils, it releases energy through the gear train, escapement, and regulating organ (balance wheel and hairspring.) When the mainspring is completely wound up, it transmits a more energy as compared to when it is nearly wound down. This difference leads to a change in precision as the watch runs. The remontoir addresses this problem by releasing energy to the escapement and balance in small, controlled amounts. Remontoir devices are understandably rare, as they are extremely difficult to engineer, manufacture, and adjust.
The remontoir is often compared with the chain-and-fusee mechanism, as both work to smooth out the delivery of energy from the barrel to the regulating organ. I asked Strehler to compare the two mechanisms. "Due to its construction with a defined fusee spiral, the chain-and-fusee only compensates a theoretical variation of the torque of the main spring but not the power variation of the real mainspring, friction variations, influences from complications, and so on. These factors can only be compensated by a remontoir, situated immediately before the escapement and acting like a filter."
Looking at Strehler's Trans-Axial Tourbillon, we can see where its name comes from. The tourbillon does not have a carriage pinion, instead it is driven by the spring on the remontoir. Unusually, the remontoir is on the tourbillon cage, and drives it, rather than one of the going train wheels; this can be thought of as the equivalent of a remontoir on the fourth wheel. The power is being transferred through the axis of the tourbillon, hence the name trans-axial. To the best of my knowledge, this is the first instance of a rementoir arranged in such a way.*
Regulating a tourbillon is notoriously difficult, but Strehler has a special technique. "To regulate the tourbillon, I use a test movement in which the tourbillon does not rotate and the escapement can be adjusted precisely. Thus, the adjustment of the hairspring and the regulation of the escapement through poising weights/screws can be [accomplished] as for a classic Swiss anchor escapement in six positions." A video showing one of Strehler's previous watches, with a similar remontoir, is included below.

Schematic of the Trans-Axial Tourbillon movement, dial side (above) and movement side (below).
While the Trans-Axial Tourbillon is a highly technical watch, Strehler did not cut back on the aesthetic aspects in any way. The three-armed tourbillon carriage is beautifully finished, with straight-graining, mirror-finish bevels, and sharp internal corners. The stud holder, which is usually overlooked or hidden from view, is instead easily visible with its graceful design. Strehler chose to use sapphire wheels for his motion work (motion works, as the name implies, are the gears that move the hands, driven by the going train) to allow more visibility inside the movement.*
Strehler is well-known inside the watch industry as the person you consult with for tough technical issues. With his Trans-Axial Tourbillon, I am hopeful he becomes well-known to the general public as an incredible watchmaker building some of the most intriguing watches in the world.
Andreas Strehler
With any remontoir watch, the absolute proof of the mechanism's effectiveness is reflected in its rate variation. A COSC certified chronometer is regulated to within -4/+6 seconds per day, but Strehler's Trans-Axial Tourbillon is on another level. "I have customers who write to me that their watch has a variation of a few seconds a week."
To learn more about Andreas Strehler, and his work, visit him online at astrehler.ch.


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