Baselworld 2015: 3 Things to Know About the Arnold & Son Constant Force Tourbillon (Updated with Live Photos)

Arnold & Son Royal---Constant-Force-Tourbillon---thumbAt Baselworld 2015, Arnold & Son introduced the Arnold & Son Constant Force Tourbillon. From what we’ve seen, there are already signs that it will give watch enthusiasts more than a couple of things to talk about.

Arnold & Son has been the center of many conversations over the last few years. It’s a small brand that shares space and personnel with the movement maker Manufacture La Joux-Perret. But that manufacturing know-how has led to some impressive watches. The Constant Force Tourbillon looks to be another piece that will have people talking. So here’s what you need to know in order to jump in the conversation.

1. The watch adopts one solution to the problem of constant force.

Constant force is a kind of grail for watchmakers: it’s the dream of an escapement that keeps perfectly even time. It deals with a lasting problem that all mechanical watches face: if a watch is powered by the energy of a wound-up mainspring, how can you keep the release of that energy perfectly consistent? As a mainspring winds down, its rate varies, and once it’s two-thirds unwound things can really slow down. So you need some extra element that will keep the flow of energy consistent. Of course, it will never be perfect, but the idea is an improvement over the normal gear train between mainspring and escapement.

Just like that other great dream, skinning a cat, there is more than one way to get (nearly) constant force. You can use a fusée-chain transmission system, which is a technology more commonly seen in pocketwatches but that still appears every so often. Another option is to directly alter the balance, as Girard-Perregaux did with its innovative spring two years ago.

Arnold & Son Constant-Force-Tourbillon_emotional-560

The third choice is what Arnold & Son selected: it’s to use a remontoire. The watch has two mainspring barrels that are mounted in serial. One of them powers the gear train; the second provides a buffer store of energy. Any time the first barrel’s torque falls below a certain point of consistency, the second barrel tops it up. This keeps the rate consistent through the 90 hours of the Constant Force Tourbillon’s power reserve.

2. The constant-force mechanism is connected to the true-beat seconds hand.

Arnold & Son is proud of its use of the true beat, or deadbeat, seconds hand. This mechanism means that the seconds hand moves exactly once per second, starting and then stopping dead sixty times in a minute. It’s an old feature and a throwback to the days of John Arnold, the company’s namesake. But it also is very hard to accomplish. In 2013 I spoke to Arnold & Son’s technical director, Sebastien Chaulmontet, about the complexity of a deadbeat seconds hand, and why the brand frequently uses them:

“A deadbeat is always complicated. … What you have to imagine: while a quartz watch is very easy, it gets an impulse every second. But with [a mechanical watch] it’s very different, because you are stopping and starting something which is moving. … The bigger it gets, the more weight you have to accelerate and stop. And it beats 36 million times a year. So it’s really a tremendous wear-and-tear problem you have to solve. Because it’s functioning all the time. It’s jumping and releasing energy and braking every second. … Even a chronograph, once you push it, it just runs. But you’re not stopping and starting your chronograph every second all day long. But basically it’s what a deadbeat is doing. It’s stopping and starting itself all day long, and you cannot stop it.”

In the Arnold & Son Constant Force Tourbillon, the deadbeat is directly connected to the constant-force mechanism. The power off of the mainspring barrels doesn’t run directly to the escapement or to the tourbillon. Instead, it goes to a smaller hairspring, which supplies a fixed amount of power to the escapement once per second. This not only regulates the flow from the mainsprings to the balance: it also is the perfect rate to power the deadbeat seconds hand. That’s why you can see the seconds hand at 7:30: it sits directly atop the constant-force mechanism. Here’s what the mechanism looks like:

Arnold & Son Constant Force Tourbillon - diagram


3. If you see a cosmetic resemblance to an earlier Arnold model, you’re not wrong.

The symmetrical, skeletonized layout of the Constant Force Tourbillon gives quite a view: you can see the two barrels at 10:30 and 1:30, the tourbillon at 4:30, and the constant-force mechanism at 7:30. Both the top and bottom pairings have matching palladium-treated bridges to hold them in place, with mirror-polished heads on the screws. For the discerning Arnold fan, this dial arrangement is a descendent of the TB88, which the brand first launched in 2011. That watch used manufacture caliber A&S 5003 and had a distinctly different set of characteristics, but the resemblance is definitely there. The two watches may even share a case: the TB88 and the Constant Force Tourbillon are among the few Arnold & Son watches with a sizeable 46-mm diameter. The Arnold & Son Constant Force Tourbillon comes in a rose-gold case.

Arnold & Son Constant-Force-Tourbillon---front_560



The Arnold & Son Constant Force Tourbillon is a limited edition of 28 pieces, all in rose gold. It has sapphire windows on the front and back. Its movement, A&S 5119, is a new caliber for the brand. It is manually wound and beats at 21,600 vph. It has 39 jewels. The watch is water resistant and comes on a brown alligator strap. Each watch costs $197,500. We snapped a few photos of the Constant Force Tourbillon at our meeting with Arnold & Son at Baselworld. Below you can see the front, back, and what it looks like on the wrist.

Arnold & Son Constant Force Tourbillon - front-live
Arnold & Son Constant Force Tourbillon - back -live
Arnold & Son Constant Force Tourbillon - wrist -live

This article was originally posted on March 24, 2015, and has been updated.

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  1. I don’t know, for a high end watch it reminds me too much of a Diesel.

  2. Debashish

    Enjoyed your report, though I can never afford to buy this watch unless I win a lottery, I think it is a fabulous watch.

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