It looks like a tourbillon. It moves like a tourbillon. It works like a tourbillon. But the TriAx mechanism at the heart of the MB&F Legacy Machine Thunderdome goes beyond the tourbillon, and when it was launched at the end of 2019, it brought a new type of rotating escapement to the conversation.
Following brand founder Max Büsser’s directive to make the “greatest, craziest triple-axis tourbillon ever,” master watchmaker Eric Coudray (a name indelibly associated with the rise of multi-axis tourbillons in the new millennium) went to work. In Coudray’s own estimation, the resulting mechanism, for which MB&F coined the term TriAx, is a hybrid between the tourbillon and karrusel systems.
The debate about which type of rotating escapement is superior has been raging for years, but here is the essential difference between the two, mechanically speaking. In a tourbillon, the escape wheel is not directly driven, but rotates as a consequence of being moved around a fixed wheel by the tourbillon carriage. In a karrusel, both the carriage and the escape wheel are directly driven by separate gear trains.
In Legacy Machine Thunderdome, the triple-axis rotating escapement combines features of both systems. Energy is delivered to the revolving cages via a dual-speed, split-train transmission that operates according to karrusel principles. The innermost cage, however, is best described as a tourbillon, due to the presence of a fixed wheel.
Then again, there are fixed wheels, and there is the fixed wheel of LM Thunderdome. Unlike conventional tourbillons, where the escape wheel rotates around the fixed wheel, the escape wheel of LM Thunderdome is the fixed wheel. As the defining aspect of a rare escapement primarily known to horological scholars as a Potter escapement – named for 19th century watchmaker and inventor Albert H. Potter – the fixed escape wheel allows for higher rotational speeds in a tourbillon.
Before 2019, the Potter escapement had only been used once before in a tourbillon wristwatch. This was the Franck Muller Fast Tourbillon of 2012, which had an awe-inspiring five-second rotational period for its single-axis tourbillon. In the example of the MB&F LM Thunderdome, using the Potter escapement in a multiaxis system was the key to its high-speed rotations – 8 seconds, 12 seconds and 20 seconds respectively from innermost to outermost rotational axes.
Inverting the geometry of the escapement allows for a larger balance, which brings greater potential for chronometric performance to the table. Supplementing this is an unprecedented hemispherical balance – which some might mistake for part of the rotating cages at first, but don’t be fooled. The difference between having a flat balance and a hemispherical one, in the given space of LM Thunderdome, is one of mass. That is to say, it is a matter of balance inertia. As you can see, it all comes back to the same thing.
All spectacle aside, all records aside, the MB&F Legacy Thunderdome is about stability of rate and chronometric precision. This watch is the result of MB&F (and Eric Coudray) setting their sights on this end goal and flooring the pedal so hard that it might have broken.
There are 50 tourbillon watches described, celebrated and explained in the pages of this books – more, if you count the honourable mentions. Many of them need that description, that celebration, that explanation, because the tourbillon is a complex beast, and any discussion of its relative merits or shortcomings can appear obscure, even impenetrable, except to diehard horological scholars. The MB&F Legacy Machine Thunderdome doesn’t need any of that to show you how special it is. Just look at it.
*This year GMT Magazine and WorldTempus have embarked on the ambitious project of summarising the last 20 years of the Tourbillon in The Millennium Watch Book - Tourbillons, a big, beautifully laid out coffee table book. This article is an extract. The Millennium Watch Book - Tourbillons is available on www.the-watch-book.com, in French and English.
