Four Part Harmony: The Innovations of Cartier's ID 2 Concept Watch: Prelude

Prelude:

Way back in 2009 I was asked to come to La-Chaux-de-Fonds along with a small group of other US-based and international journalists to take a look at Cartier's ID One Concept Watch.

We didn't know what to expect; as with ID Two, Cartier did an excellent job of keeping us all in the dark, and what we saw was a remarkable achievement: a watch which would require no adjustment, either during its assembly and initial setup, or during the course of its operating life.

To understand ID Two, it's first necessary to understand ID One, and to understand ID One, it's necessary to understand the problems that ID One was built to address. These problems are as old as watchmaking itself, and have preoccupied its finest minds, from Mudge, Harrison, Breguet, Huygens, Guillaume, and so on down to the present day. It was to address these problems that the tourbillon, remontoire d'egalite, compensating balance, and modern hairspring alloys were invented.

The Problem of Adjustment

Adjustment is the process of fine-tuning a watch to the greatest possible accuracy, and greatest possible stability of rate. The length and concentricity of the balance spring, depth of pivot jewels, amount and distribution of lubricant, depth with which the pallet stones on the lever interact with the escape wheel teeth, shape of the balance spring terminal curves, configuration of the regulator index pins, and so on are all aspects of the watch that can be controlled by a watchmaker in order to produce a watch which has the desired properties. Among these are:

--stability of rate (that is, the watch will not start to run faster or slower over time)
--minimum deviation of rate between positions (something that can be minimized but which is nearly impossible to eliminate entirely)
--stability of rate across an expected range of ambient temperatures
--stability of rate across the running time of the watch (that is, the watch should run at the same rate at the beginning, middle, and end of its power reserve.)

The number of things to tweak are considerable but the basic adjustments are often engraved (with pardonable pride) on the movement of a watch that has benefited from them; a high grade watch may say, "Adjusted to isochronism, temperature, and 5 positions."

Most of the history of precision watchmaking has revolved around trying to find solutions to these three problems: temperature, isochronism, and stability of rate across various positions. Many of watchmaking's cleverest inventions have been attempts to address these problems --as was ID One.



Isochronism was a huge problem with the earliest escapement used in clocks and watches: the verge. The verge is a so-called "frictional rest" escapement and in addition the earliest clocks and watches had no balance spring. Thus the verge escapement's rate was a slave of the torque in its spring. The most revolutionary development in watchmaking was the addition of a balance spring, pioneered by Huygens and Hooke in the late 17th century, which opened the door to the development of real precision timekeeping. Subsequently other refinements were tried as well. The chain-and-fusee, the remontoir d'egalite, constant force escapements, and the use of stop works on the mainspring barrel which prevent the final (weak) turn of the mainspring from powering the watch are all methods of ensuring even torque to the escapement. Theoretically the balance and spring combination should be perfectly isochronous but for it to be so, the system would have to be ideal (immune to temperature changes, perfectly concentric, the inner terminal curve exactly at the center of the axis of the balance staff, etc.) and so the search for various ways to ensure isochronism has continued. (The modern automatic or self-winding watch is a kind of remontoir d'egalite and if worn daily will deliver reasonably even torque.)

Temperature changes cause changes in the modulus of elasticity of the hairspring (and also changes in the viscosity of oils, although the change in hairspring elasticity is the main issue in temperature adjustment.) The observation that brass and steel have different coefficients of expansion led to the invention of the compensating balance in precision pocket watches. This type of balance (identifiable by the two cuts in its rim and its brass-steel sandwich construction) increases or decreases in diameter as the temperature changes, compensating for the increase or decrease in the elasticity of the steel balance spring (for instance, if ambient temperature increases, the balance spring becomes less elastic and the rate slows; the compensation balance responds by decreasing in diameter, producing an increase in rate, like a figure skater drawing in her arms to turn faster.) The compensation balance was very expensive to produce and adjust, and as well, the degree of compensation was not perfect, and so further developments led to alloys like Glucydur for balances, and Nivarox-type alloys for the balance spring, which have extremely high dimensional stability across a wide range of ambient temperatures and provide excellent performance; such balances made the charming but troublesome plain steel balance spring and cut compensating balance obsolete.

Stability of rate across positions is vulnerable to the effects of gravity on escapement components. The effect of gravity on the balance pivots, as well as the amount of lateral pressure produced on the balance pivots by the "breathing" of the balance spring coils, the shape of the outer terminal curve of the balance spring and point of attachment of the inner curve, and the parallelism and position of the regulator index pins are all considerations in making the rates at which a watch runs in various positions as close as possible. Like temperature adjustment, however, perfect stability of rate across positions is in practice never achieved. One of watchmaking's most famous inventions, the tourbillon, was and is intended to address this problem by creating a single average error across all vertical positions, which could then be (relatively) easily compensated matched to the rate in the flat (horizontal) positions by slightly flattening the tips of the balance pivots to create friction in the flat positions that approximates that in the hanging positions. Theoretically this should work but in practice the difficulty of constructing the tourbillon to the necessary precision, as well as the additional demands of poising the carriage perfectly, the extra inertial problems created by the need to stop and start the mass of the entire carriage at every swing of the balance, and the compromised geometry of the traditional, side-lever configuration of a classic tourbillon, have conspired to make the tourbillon a solution that delivers only on those rare occasions when it has been made and adjusted to the highest standard of skill. The inclined tourbillon as well as modern multi-axis tourbillons are intended to improve on the conventional tourbillon for use in a wristwatch (as opposed to a pocket watch) but they are even more complex, and as Stephen Forsey of Greubel Forsey once said to me, "It's always a struggle to gain more than you lose."

Finally, a word about magnetism. Magnetic fields can exert a dramatically negative effect on a watch and even though modern Nivarox type alloys are relatively unaffected by magnetism a really strong magnetic field --like that created by the powerful magnets used to keep purses and cell phone cases closed, for instance --can magnetize even a modern hairspring and cause a watch to run dramatically inaccurately. If the escapement components are steel the watch can be stopped completely by a strong enough magnetic field. Finally, magnetic fields exert a more subtle but equally pernicious effect.

It is not often realized that the ability of a modern balance spring alloy to compensate for temperature changes is affected by the degree to which it absorbs magnetic field energy. This energy is absorbed, to quote an article by the inventors of the Carbontime carbon fibre balance spring "in a cumulative manner . . .after a time, the elasticity of the spring changes, and isochronism is adversely affected."

To make a watch that requires no regulation, therefore, means making a watch as unaffected as possible by temperature, changes in position, and which is as close to ideally isochronous as possible without having to manually readjust any part of the watch to bring it within the desired performance envelope.

It was to address this problem that ID One was created. ID Two extends the work done on ID One, by addressing four aspects of the watch: the power source, going train, escapement, and case --hence the title of this series, in which we will look at the four areas of innovation in ID Two.

Jack

PS: for those interested in really digging into the subject I highly recommend Walt Odet's classic Timezone series, "Tweaking the Mark XII." in which he describes the nearly 50 hours he spent adjusting an IWC Mark XII ("every non-pilot's favorite pilot's watch.") He expands on many points I only touch on here or don't address at all --including the critical one that while a properly adjusted watch is considered high grade, only a high grade watch can be adjusted in the first place.

PPS courtesy GEO this series will be sticky'd as it goes up, just to keep everything in one place. Thanks GEO!



Edited 4 time(s). Last edit at 07/15/2012 09:34PM by Jack Forster.