How It Works: The Urban Jürgensen 250th Anniversary UJ-1, Tourbillon With Remontoir

The recent relaunch of Urban Jurgensen is nothing if not ambitious. The company launched its first three watches in Los Angeles, under the leadership of Kari Voutilainen and Alex Rosenfield, with the stated ambition of creating watches made to the very highest possible standard, and which connect to both the earlier years of watchmaking at Urban Jurgensen (which begin with the return of Urban Jürgensen to Copenhagen in 1801, after a traveling apprenticeship that included working under Houriet, Breguet, Berthoud, and John Arnold) and, to later work done by Derek Pratt, the English watchmaker responsible for creating perhaps the most highly regarded watch from Urban Jurgensen in its more recent history. This oval pocket watch is extraordinarily beautiful both in its aesthetics, and in terms of the craftsmanship and ingenuity demonstrated in its watchmaking.

The Pratt oval pocket watch, whose design shows the obvious admiration Pratt had for the work of Abraham Louis Breguet, was begun by Derek Pratt in 1982; due to illness, he was unable to complete the watch, and in 2004, he turned the nearly finished project over to Kari Voutilainen, who completed it in 2005. The watch was in the collection of Dr. Helmut Crott, until it was sold at auction by Phillips in 2024, where it hammered for CHF 3.69 million.

There is really nothing that is not exceptional in the strongest sense of the word about the Oval, including the – painstaking is putting it too mildly, but let’s say, painstakingly applied and highly complex guilloché on the dial – and, of course, including the movement, which was created by Pratt entirely by hand, with no aid from computer guided milling machines. The movement is constructed so that it is essentially completely visible from the mainspring barrel to the tourbillon, escapement, and balance; and the usual upper movement bridges have been reduced to a single, tapering cylindrical bridge for the great wheel of the going train. Both the mainspring barrel and tourbillon are “flying” which is to say, fixed only at the base with no upper bridge, and the balance is enormous, nearly the diameter of the mainspring barrel itself.

For the UJ-1, Voutilainen, who as co-CEO is handling all of the watch design and watchmaking for Urban Jürgensen,  set himself the task of re-creating the Oval movement, but in a round wristwatch.

The design of the watch as seen from the dial side is soberly restrained; the gulloché is extremely fine, but especially the Clous de Paris pattern on the subdial for the small seconds. For the new watches, UJ has foregone even the very slightly baroque air of the teardrop lugs characteristic of earlier Urban Jürgensen wristwatch production; nonetheless, the 39.5mm x 12.2mm watch seen from the front is a clearly very fine piece of work, but one which sets expectations very high for what’s on the movement side.

Those expectations are met, and then some. The movement, Urban Jürgensen caliber UJ-1, is 30mm x 8.17mm, and duplicates the architecture of the Oval almost exactly, right down to the relative proportions of the mainspring barrel and flying tourbilon. The watch has a 47 hour power reserve, and runs at 18,000 vph and like the Oval, the mainspring barrel and tourbillon are both flying; the UJ-1 uses the same tapering cylindrical steel great wheel bridge found in the Oval as well.

Finishing as you might expect from anything to which Voutilainen has put his hand, absolutely impeccable. The style of finishing is not the usual Swiss-French style, which uses brightly sparkling nickel, German silver, or rhodium-plated brass components, finished with Geneva stripes. Instead, it echoes the gilt and polished steel vocabulary found in both traditional high end English watchmaking, and in the work of Abraham Louis Breguet, who was so influential in the work of both Pratt and his more famous colleague, George Daniels (who famously and disdainfully wrote that when watchmakers have no real problems to solve, they distract themselves by producing a jewel-like finish).

The dial side of the UJ-1 movement is so wonderfully handled that it makes me wish that the watch came with some sort of hinged dial, to allow the owner to see it (albeit such an idea is absurd, it would be totally impractical; you’d have to pop off the hands, but still, a person can dream). In the image above, the pivot for the small seconds hand is at the top, with the rack and tension spring for the power reserve at the bottom. The under-dial works make use of rose gold plating, and a combination of straight grained and grenage finishing on the bridges, with straight grained steel for the two cocks. Everything is done with absolute fidelity to the practices of traditional watchmaking – even the outer curve of the spiral power reserve tension spring, is pinned to its stud using the friction fit pinning technique used to affix the inner terminal curve of a balance spring to its collet.

The opposite side of the movement showcases the same level of attention to detail – naturally – and also showcases the signature element of the Oval, which is the remontoir d’égalité. The latter is a constant force mechanism, which regulates the amount of power delivered from the mainspring to the escapement and balance, and it’s one of the most difficult regulating mechanisms to make, as well as one of the rarest. There are considerably fewer watches with remontoirs than there are with tourbillons (which is, now that I think of it, not setting the bar as high as it would have been in the pre-Quartz Crisis years when tourbillons were rarer than hen’s teeth, but you get the idea).

The remontoir was invented in order to solve a problem, which is that, as a mainspring winds down, it delivers less and less power to the escapement and balance. When the remontoir was first invented (John Harrison developed the first spring remontoir for his experimental H2 marine chronometer) most watches used the verge escapement, which is highly sensitive to power variations as the verge’s escape wheel is in constant contact with the pallets on the balance staff. The remontoir is less necessary in watches with escapements that only contact the impulse surface of the balance when impulse is given, but they are still a demonstration, if anything is in watchmaking today, of traditional watchmaking craft.

A remontoir can be thought of as a kind of supplementary, smaller mainspring, which is wound up periodically by the primary mainspring. The remontoir spring sits somewhere between the mainspring and the escapement, on one of the train wheels, and drives that train wheel; since it’s rewound periodically, it gives constant torque for the entire power reserve of the watch, or at least as long as there is enough torque in the mainspring to rewind the remontoir spring. Most remontoirs are on either the fourth wheel or the escape wheel, and if they rewind at a very short interval (in watches and clocks they can rewind as infrequently as an hour, or as frequently as one second) they can be used to drive a deadbeat seconds hand.

The remontoir is rare, costly, and difficult to make but Pratt, in the Oval, did something which had never been done before, which was to place the remontoir on the escape wheel – and inside the tourbillon cage.

This configuration has been duplicated in the UJ-1 caliber. Tourbillon watches were, historically, difficult to make and adjust, because of the additional inertia of the escapement, escape wheel, and cage, all of which have to move every time the escapement unlocks. (In an ordinary watch, the energy at unlocking need only drive the escape wheel, lever, and balance, which is one of the reasons the tourbillon has been regarded by some horologists as an undesirable parasite). Putting the remontoir inside the cage means that the remontoir spring need only overcome the inertia of the lever and balance – it is, in fact, a pretty neat magical vanishing trick; it’s as if the tourbillon cage isn’t there at all.

The whole assembly can be seen more clearly with the tourbillon cage removed from the UJ-1 caliber and viewed on its own.

We can first of all, admire the level of workmanship visible, and we can now also see the relevant components. The balance is freesprung, with a Phillips overcoil balance spring and with the escape wheel and remontoir wheel visible at the lower right. The tourbillon completes one full revolution per minute, and therefore can have on its pivot, on the dial side of the watch, the seconds hand, about which more in a minute.

Here’s how it works. The escape wheel rotates under the power of the remontoir spring, with its teeth giving impulse to the escapement lever’s pallets in the usual manner. As the escape wheel rotates, it also causes a three lobed, Reuleaux triangle mounted on its pivot to rotate as well. As the Reuleaux triangle rotates, its shape causes the remontoir fork to move laterally, which periodically lifts the remontoir pallet (there are actually two pallets, just as in the escapement lever) off one of the three teeth of the remontoir wheel. As the wheel unlocks, the whole tourbillon cage, which is driven by a pinion on its underside by the going train, is unlocked and free to rotate. This causes the remontoir wheel, whose pinion works against the fixed fourth wheel teeth under the tourbillon cage,  to rotate one third of its diameter, until it’s locked once again by the remontoir lever, which has continued to move under the influence of the Realeaux triangle’s rotation on the escape wheel. This winds the remontoir spring, which continues to deliver torque to the balance via the lever. The entire cycle takes one second and the tourbillon rotates six degrees, from unlocking to locking.

The escape wheel and remontoir wheel rotate independently from each other, so that the remontoir wheel can be locked in place while the escape wheel is rotating – in fact if this were not so, the whole system wouldn’t work; the locking of the remontoir wheel tooth against the remontoir pallet performs the same function for the remontoir spring, as the click does for the mainspring in a conventional watch, allowing the spring to remain under tension and direct power to the escape wheel. As an additional feature, the remontoir, as we mentioned, unlocks once per second and since during that second, the tourbillon rotates six degrees, the seconds hand, which is on the pinion of the tourbillon cage, also jumps one second – you get a deadbeat seconds as a bonus.

The Reuleaux triangle is a rather special object, whose geometry is indispensable for the remontoir.  Despite its being a triangle, it has a constant width.

In a Reuleaux triangle, each of the three curved sides is a segment of a circle of a constant radius (well, it would be constant, otherwise it wouldn’t be a circle!) whose center is the vertex of the opposite triangle.

Somewhat counterintuitively, this means that the Reuleaux triangle can placed inside a rectangular enclosure of fixed width, and as it rotates, it will cause the enclosure to oscillate back and forth, converting the rotation of the triangle to lateral motion.

It’s pretty nifty. In his original design for the Oval, Pratt at first used a steel Reuleaux triangle inside a steel remontoir lever, but he apparently became concerned about the friction of steel against steel in such a rapidly rotating part, and for the Oval, he made the Reuleaux triangle out of synthetic ruby. Voutilainen, who was obviously aware of the issue, used a steel Reuleaux triangle, but placed jewels on both the inner surfaces of the part of the remontoir lever enclosing the triangle. The Reuleaux triangle is a useful shape – it can rotate inside a rectilinear enclosure of fixed width but the converse is also true; Reuleaux triangle shaped drill bits can be used to drill holes that are square in cross section. A Reuleaux triangle-shaped piston was also used in the short lived, but intriguing, Wankel rotary engine.

Well, there you have it – beauty and brains, what more could you ask? This is a wonderful example of the life of ideas in watchmaking and how the ingenuity of generations of watchmakers continue to give their inventions and by extension, the watchmakers themselves, a kind of immortality; it is worth reflecting on the lineage of problem solving which the spring remontoir represents, from Harrison through Pratt and down to Voutilainen, who took the torch of the problem of putting a remontoir inside a tourbillon from Pratt, and gave it new life in the UJ-1. The first time I ever fixed a pocket watch (a million years ago, When Dinosaurs Ruled The Earth) and it began to tick on my kitchen table, I felt my hair stand on end; it was as if whomever the unknown watchmaker who had first brought it to life a hundred years ago, was standing invisibly behind me, looking over my shoulder. So it is with the UJ-1 – a reminder that the best way to honor the work of a mechanical genius like Pratt, is to give new life to their ideas.

Recommended reading: “A Closer Look: The Derek Pratt Oval Pocket Watch,” at Revolution; Derek Pratt’s Reconstruction Of John Harrison‘s H4, The World’s First Precision Marine Chronometer, at Quill & Pad; In-Depth: The Unique and Magical Oval Tourbillon Watch by Derek Pratt, at Watches by SJX.

The Urban Jürgensen UJ-1: case, 39.5mm x 12.2mm, in platinum or rose gold, water resistance 30 meters. Dial and hands, galvanic treated solid silver, with Grain d’orge and Clous de Paris guilloché. Movement, caliber UJ-1, flying tourbillon with one second remontoir on the tourbillon cage and deadbeat seconds; 47 hour power reserve, running at 18,000 vph in 32 jewels, 30mm x 8.17mm; flying tourbillon and flying mainspring barrel. All three watches are limited editions of 25 pieces; price, CHF 368,000. See the UJ-1 at Urbanjurgensen.com.