H. Moser x MB&F Endeavour Cylindrical Tourbillon
“This watch has it all.” – Tim Mosso
The H. Moser & Cie. Endeavour Cylindrical Tourbillon is an unusual watch on several counts. First, of course, it is a tourbillon and while the tourbillon exists in numbers today which would have made Abraham Louis Breguet’s wig fly off, it is still a rare mechanism. Secondly, it is a self-winding tourbillon, which is quite unusual, although not especially technically difficult – self-winding, or automatic, tourbillons have only been around since 1986, when Audemars Piguet introduced the ultra-thin (or extra-flat, if you prefer – the two terms are more or less interchangeable, although “ultra” sounds more, well, ultra) caliber 3870. This was not only the first series produced tourbillon wristwatch, but also the thinnest, right up until Bulgari broke the long-standing record in 2018 with the Octo Finissimo Tourbillon Automatic.
Finally, it’s one of a very small number of tourbillons with a cylindrical balance spring. The balance spring (or hairspring, if you like, as with ultra-thin vs. extra flat, I just think “balance spring” sounds more dignified) is the tiny spiral of metal responsible for returning the balance to its neutral position as it oscillates.
Cylindrical balance springs, and the even rarer spherical balance spring, have been used very rarely in any tourbillon wristwatch – Jaeger-LeCoultre has used both in tourbillon watches, in, for instance, the Duomètre à Sphérotourbillon. (I have an old copy of Britten’s Watch And Clockmaker’s Handbook which disparages the spherical balance spring as a “pure freak” of no actual practical value but by god, they look cool).
Most balance springs are flat spirals of metal. Somewhat less common is a balance spring with a so-called Breguet overcoil, which is also sometimes called a Phillips overcoil as the mathematical foundation for the Breguet overcoil was finally established by an horologist, mathematician and physicist named Phillips, in 1861).
The balance spring does for the balance what gravity does for a pendulum clock – technically speaking, it acts as a “restoring force” on the oscillator and a pendulum, or balance, will keep precise time as long as the restoring force is directly proportional to the driving force. That is, gravity pulls back on the pendulum harder if the pendulum is pushed harder, which means that no matter how wide the swing is, it will always take the same amount of time. In watches, since the restoring force is not gravity, you can only approximate a proportional relationship between driving force and restoring force but a good modern watch can get very close.
A flat balance spring, as it oscillates, would ideally breathe, or contract and expand, perfectly concentrically but in practice flat balance springs will tend to breathe asymmetrically. This is a problem as the asymmetrical expansion and contraction will push the pivots of the balance against their bearings, which will cause wider variations in rate across various positions. To get the balance spring to breathe concentrically, you can shape the outermost coil into a Breguet overcoil and many high grade, precision-oriented watches use an overcoil balance spring (Rolex uses over coils across most of its production).
The cylindrical balance spring attempts to go the Breguet overcoil one better – in a sense, the cylindrical balance spring is nothing but overcoil. A cylindrical balance spring is, as the Brits say, just what it says on the can – it’s a balance spring in the shape of a cylinder rather than in the shape of a flat spiral, or a flat spiral with overcoil. The cylindrical balance spring was invented by the English watchmaker John Arnold, in 1776, and was widely used in marine chronometers. Cylindrical balance springs also have overcoil inner and outer terminal curves, because when you are pursuing fractions of a second in precision, why not take every margin you can get?
The H. Moser Endeavour Cylindrical Tourbillon combines a cylindrical balance spring with a tourbillon. Both inventions are regulating systems which are intended to minimize the negative effects of changes in rate across positions but they go at it in different ways. The tourbillon produces an average rate of all the vertical positions, which can then be more easily matched to the rate in the flat positions and the cylindrical balance spring reduces the effect of changes in position, by eliminating (or nearly eliminating) the lateral push on the balance pivots you get with a flat balance spring.
H. Moser & Cie. has the advantage of having a manufacturing arm – Precision Engineering AG – which can produce balance springs in relatively large numbers, for both Moser and for other watch brands. The balance spring is very difficult to manufacture as you have to be able to produce them with great consistency – any apparently minor variations in the composition of the alloy or the physical dimensions of the spring will be amplified enormously in a watch, which is why to this day, so many balance springs are supplied by Nivarox. Nivarox, owned by the Swatch Group, makes balance springs and escapement components which are essential to many dozens of brands and, probably, millions of watches a year but they have never, nor will they ever as far as I know, invite journalists to visit their factory.
Bringing balance spring production “in-house” became a major priority for many brands starting in the early 2000s, as a way of reducing dependency on outside suppliers and Precision Engineering AG means Moser doesn’t need to go to Nivarox for balance springs. It also means that exotic shapes like the cylindrical balance spring can be produced on demand.
As the name says, the H. Moser x MB&F Endeavour Cylindrical Tourbillon Endeavour Cylindrical Tourbillon mechanism was a collaboration with MB&F, and the watch was made in extremely small numbers – only fifteen pieces overall, with three pieces each in one of five fumé dial colors. The overall architecture is taken from the Legacy Machine LM10, but with some significant engineering differences (the LM10 has a very large balance oscillating above the dial on what must be the longest balance pivots ever used in a wristwatch). The shape of the LM10 domed crystal gave plenty of, you might say, breathing room for the cylindrical balance spring which of necessity takes up a lot of vertical space in the movement, but in the Endeavour Cylindrical Tourbillon, this is a feature, not a bug – the domed crystal ensures that the cylindrical balance spring flying tourbillon can really be seen and appreciated in three dimensions.
Aside from all the technical bells and whistles there are a lot of wonderful little design details as well – the watch was designed so that it can be worn with either the tourbillon, or the dial, facing the wearer and the transparent sapphire dial is fully lumed, including the logo. Tim Mosso said in his video review that this watch has it all, and it really does – it’s a very small batch limited edition from two of the hottest names in independent horology; it’s got technical chops equalled by very few other wristwatches and even very few other tourbillon watches, and on top of everything else, it’s one of the sweetest pieces of mechanical eye-candy anyone could wish for. If you’re looking for a watch that has so much fantastic horological content that it need bow down to no other watch on the planet, you can stop looking.