Up Close: Purnell Escape II Double Tourbillon

Ingenious and double-triple axis.

Given that the tourbillon was invented for the pocket watch, adapting Abraham-Louis Breguet’s invention for the wristwatch opened the floodgate for tourbillon innovations in the beginning of the 21st century – the golden age of the tourbillon, perhaps technically but surely commercially. In fact, many watchmakers have gone far beyond the traditional concept of a tourbillon since English watchmaker Anthony G. Randall invented the double-axis tourbillon in 1978.

But as the years passed, tourbillons evolved into elaborate constructions seemingly just for the sake of visual complexity. And there have been so many of them. For this reason, exotic tourbillons now seem dated, with sophisticated or truly interesting technical solutions being hard to come by.

Potter and Purnell

But the latest development in tourbillons is one of the most intriguing of recent times: maximising the visual effect of a tourbillon regulator not just by multiplying the axes of rotation, but speeding them up with the use of a specialised escapement invented two centuries ago by Albert H. Potter, a highly regarded American watchmaker based Geneva.

The full potential of the Potter escapement was recently realised when it was combined with a carrousel outer cage in the MB&F LM Thunderdome, the world’s fastest rotating triple-axis tourbillon. But the concept was first applied, arguably in a more elaborate manner, in the Spherion tourbillon of Purnell – which was developed by the same watchmaker behind the MB&F creation.

Formerly known as Cecil Purnell, the brand is named after a British soldier of the First World War who settled in Besançon, the historical centre of French watching, after the Great War. There he learnt watchmaking, though the eponymous brand was only founded in 2006 by his grandson, Jonathan Purnell, a long-time watch and clock dealer.

Purnell has only ever produced tourbillon wristwatches, albeit of varying quality. The brand started off in an inauspicious manner, relying on entry-level tourbillon movements in relatively inexpensive watches. But Purnell made a major and impressive move upmarket with the breakthrough triple-axis Spherion tourbillon in 2016.

Equipped with the Potter escapement, the Spherion’s innermost cage rotates at lightning speed, once every eight seconds. And last year Purnell debuted the Escape II Double Tourbillon that is a Spherion squared – twin, high-speed triple-axis tourbillons.

Enormous but artfully airy 

Available in titanium or 18k rose gold, the case of the Escape II is massive – 48 mm in diameter and 19 mm thick – a necessity due to the complicated movement, which contains not just the double tri-axial tourbillon, but also six mainsprings. And it looks thick, because the case sides are vertical and the bezel almost flat; wide fluting on the case flanks further emphasise the height.

Naturally, the Escape II much more wearable in lightweight titanium, and the short, curved lugs do help with the fit, which is better than the dimensions suggest.

But in the realm of uber-tourbillon watches, such size is par for the course – such watches are meant to make a point. Greubel Forsey‘s more classical creations are rarely smaller, likewise for the Vacheron Constantin Armillary Tourbillon. And the flamboyant Jacob & Co. Astronomia is 50 mm wide and 26 mm thick.

The case band accentuates the height

Importantly, the case is large for a reason.

To highlight the three-dimensionality of the movement, the case is topped by domed sapphire crystal that extends downwards at six o’clock, until the strap, ensuring both tourbillons are visible even when the watch is on the wrist. And the case band is also inlaid with a large sapphire panel that reveals profile of the movement.

Tourbillons visible on the wrist

And also from the side

One of the most striking aspects of the movement is its theatrically open-worked architecture. The time display, power reserve indicator as well as transmission system occupy the top half of the movement, leaving a generous negative space for the twin tourbillons, which are each suspended at one end from a cubic bridge that houses the differential connecting the two.

The dial is black ruthenium with lacquered indices

The tourbillons each on a single pivot connected to the cubic bridge

The Potter escapement

The technical genius responsible for both the Purnell Spherion, and subsequently the MB&F Thunderdome, is Eric Courdray. Now in charge of complications workshop TEC Ebauches, Mr Coudray is best known for creating some of the definitive tourbillon movements during the early 2000s heyday of the complication, most notably the Jaeger-LeCoultre Gyrotourbillon that made headlines when it was first unveiled in 2004.

Perhaps Mr Coudray’s most exotic tourbillon to date, Purnell’s Spherion is a triple-axis tourbillon made up of three nestled cages, with the escapement and balance wheel mounted on the innermost cage. The theory behind this construction is the same as that for all multi-axis tourbillons: the combined axes of rotation of all three cages is more effective at averaging out gravitational errors as it exposes the balance wheel to a greater variety of positions.

Mr Coudray’s recent multi-axis tourbillon, including the MB&F Thunderdome, are distinctive due to the rapid rotation of the cages, offering an animated spectacle to the user. The Escape II doubles down with twin, triple-axis tourbillons.

The three cages, from inner to outermost, in yellow, red and blue respectively. Photo – Purnell

The high speeds are made possible thanks to a very particular escapement designed specifically for tourbillons by Albert H. Potter (1836-1908), a New York native who moved to Geneva in 1875.

Though mostly unknown today, Potter was a prominent watchmaker in his day who made extremely distinctive pocket watch movements with organically shaped bridges. Though he produced watches in small numbers, Potter was a prolific inventor. Besides the tourbillon lever escapement, the American also invented an inclined tourbillon as well as an improved version of the pivoted detent escapement.

By design, a conventional tourbillon completes a rotation every 60 seconds, which allows the cage to double as the seconds display. Such a construction revolves the escapement – namely the balance wheel, pallet fork and escape wheel – around a fixed fourth wheel. During the tourbillon’s rotation, the escape wheel meshes against the fourth wheel via a pinion, which acts as a reduction gear that trims the speed of the tourbillon to 60 seconds per revolution.

To speed things up, a redesign of the entire mechanism is required. Potter achieved this by cutting the number of components, doing away with the fixed fourth wheel and escape wheel, replacing them with a single, fixed escape-wheel ring with inward facing teeth. The balance wheel and pallet fork interact directly with the escape-wheel ring, without any reduction-gear pinion, allowing for much faster rotation – eight seconds in the case of the Purnell Spherion.

The Potter escapement with its defining large, fixed escape wheel with inward facing teeth. Image – MB&F

The escape wheel is fixed to the second cage (in red). Image – Purnell

The rapid rotation of the innermost cage in the Purnell Spherion triple axis tourbillon is possible only with the Potter escapement. With reference to the image above, the fixed escape wheel is mounted on the middle cage (in red). The innermost cage (in yellow), containing the balance wheel and pallet fork, is driven by rotation of the middle cage. And the middle cage, in turn, is driven by rotation of the outermost cage (in blue). And finally, because there are a pair of outer cages, both are driven directly by the movement with energy from the barrels split by a differential.

A similar construction utilising the Potter escapement in a multi-axis tourbillon is found in the recent MB&F LM Thunderdome, making it an inevitable comparison.

But there is a crucial difference between the Spherion and Thunderdome: the latter achieves its speed by also incorporating a carrousel in the outermost cage. Also, since the Thunderdome has a highly-domed crystal giving the movement more vertical volume, it has a large cylindrical hairspring and hemispherical balance wheel. In contrast, the Spherion features a more conventional set-up of a flat hairspring and free-sprung balance wheel.

The MB&F LM Thunderdome with its cylindrical hairspring and hemispherical balance

However, the Escape II distinguishes itself with a pair of triple-axis tourbillons. This makes it the fastest double triple-axis tourbillon to date – pitted against an admittedly narrow field of competitors – with the three cages rotating at the impressive speeds of 8, 16, and 30 seconds per revolution. Collectively, the three cages will return to their original positions after 240 seconds – the lowest common multiple of the periods of each cage.

Incorporating additional axes of rotation into a tourbillon is ensuring the delicate equilibrium of weight, size and power. Naturally, a double, tri-axial tourbillon requires a tremendous amount of torque to keep it going while maintaining stable timekeeping.

Thus, to reduce energy consumption, the cages are made of titanium for lightness, and lacquered in red for visual effect. At the same time, the movement is equipped with a total of six barrels – arranged in two side-by-side stacks of three that unwind in parallel, offering a 32-hour power reserve. The short power reserve, despite the many mainsprings, illustrates how energy intensive the double tourbillon regulators are.

The barrels visible through the window at 12 o’clock

The six barrels directly and simultaneously drive the second wheel via a long pinion, which also carries the minute hand directly. Visible on the dial, within the chapter ring for the time display, are the motion works for the hour and minute hands.

Unlike almost everything else about the movement, the gear train is almost entirely hidden, but it culminates dramatically in a full-fledged differential with bevel gears that links both tourbillons. That’s an uncommon feature as bevel-gear differentials require significant thickness, something most constructors try to avoid. As a result, movement designers usually turn to a planetary differential, which is flat.

On the subject of differentials, it’s important to note that the differential drives the tourbillons, and not vice versa. The differential splits the power from the mainspring, apportioning the energy to each tourbillon, while averaging their respective errors to produce a single output for the time display. So if one tourbillon gains three seconds and the other losses three seconds, the result is a perfect zero deviation. But as it is with most ultra-exotic tourbillons, chronometry is hardly the point, since the Escape II lacks a running seconds.

Due to the short power reserve, the power reserve indicator on the Escape II is a useful feature since it reminds the wearer to wind the watch daily.

Sitting below the left barrel is the cone and feeler mechanism for the power reserve, which has its origins in 18th century marine chronometers – an ironically traditional mechanism in an ultra-contemporary watch.

The power reserve display, with the conical differential just beneath

As opposed to the more common and compact differential system that relies on a planetary gear, this slightly more elaborately mechanism relies on a cone that’s driven up and down by a screw linked to the barrel. The cone is linked to a feeler that measures the motion of the cone and transmits the state of wind to the power reserve hand just above.

Side view of the power reserve mechanism with the top of the cone visible

Even though the power reserve is short, the half-dozen barrels require a bit of extra mechanics to wind. Visible through the case back, the crown wheel does not drive the ratchet wheel directly as in a conventional movement.

Instead, a reduction gear train links the crown wheel to the barrel ratchet wheel. When the watch is wound, the reduction gears reduce the turning speed from the crown, but proportionally amplifies the torque in order to wind six barrels simultaneously, which would otherwise require impractical effort to wind due to the enormous resistance created by the six mainsprings.

The reduction gear train on the left links the crown to the intermediate wheel in the middle, which in turn winds the barrel ratchet wheels on each side

Décor

With most of the movement finished in a flat black, little stands out decoratively.

One distinctive element of the movement are the pair of barrel covers, visible through the dial, which have been relief-engraved with inscriptions of Purnell’s watchmaking philosophy – a feature no doubt borrowed from Greubel Forsey. The laser-engraving is executed to a fine resolution with defined inner angles of the serifs.

But the most striking component is unquestionably the bright red tourbillon cages. The outermost cages of both tourbillons are coated in shiny lacquer, giving them an unusually organic look. The red cages highlight the rapid rotation of the cages, even from afar, creating a striking visual display.

Glossy red is one of the many looks available; the outermost cages can be customised in finish and colour, including heat treatment or metal deposition. But the aesthetic of the two techniques will result in a more geometric and angular structure that looks metallic, much like the Gyrotourbillon or the Thunderdome, with only the varying thickness of the lacquered finish that creates the novel organic appearance.

As with many ultra-contemporary watches, the movement of the Escape II is mostly machine-finished. And as with many ultra-contemporary watches, the decoration is appropriate for the style but not the price.

One of the six mainsprings, visible through the open-worked barrel cover

At bottom, one of the reduction gears for winding

The keyless works for winding and setting

Concluding thoughts

Appropriate pricing in the bizarre world of extravagant and extreme, high-end complications isn’t always logical, but it is usually sensible.

At 425,000 Swiss francs, the Escape II Double Tourbillon costs over 50% more than the MB&F LM Thunderdome – a fair premium given the complexity and demands of doubling the flying, triple-axis tourbillons.

However, there is one watch that has the upper hand in the value stakes – the Jacob & Co. Twin Turbo Furious. For 100,000 francs extra, the offering from Jacob & Co. boasts a decimal minute repeater and a mono-pusher chronograph in addition to the pair of flying triple-axis tourbillons.

That said, the Escape II is technically impressive, unusual in conception, and outstanding in visual effect. Ultimately, the real intrigue lies in its use of an esoteric 19th century escapement – one that was clearly ahead of its time – to achieve an unapologetically modern-day pursuit – a high-speed tourbillon. That itself offers a surprisingly meaningful and sophisticated perspective on watchmaking past and present, which might be sufficient to transcend complexity and showmanship.


Key facts and price

Purnell Escape II Double Tourbillon

Diameter: 48 mm
Height: 19 mm
Material: 18k rose gold or titanium
Water resistance: 30 m

Movement: Cal. CP03
Functions: Hours, minutes, power reserve display; double triple-axis tourbillon regulators
Frequency: 21,600 beats per hour (3 Hz)
Winding: Hand-wind
Power reserve: 32 hours

Strap: Rubber or crocodile

Limited edition: 20 of each variant
Availability:
 Direct from Purnell or at its authorised retailers
Price: From 425,000 Swiss francs

For more, visit Purnellwatches.com.


 

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