Why Two Balance Springs are Better than One
With an extra balance here and a second gear train there, watches go after horological perfection by stepping out of the proverbial box
Just like the human body, a mechanical movement has a core anatomy. Typically, it includes a mainspring coiled within a barrel and a going train that consists of four gearing wheels, the escapement, and the balance wheel. Science has proven that larger brains equate to higher intelligence, so it stands to reason that having two brains is very likely better than just one.
It is the same for mechanical watches. When done well, having two balance wheels (or more) yields higher timekeeping accuracy and additional barrels understandably give more power. A set of gongs that encircle the movement twice, also known as cathedral gongs, produces chimes with greater resonance, color, and richness as opposed to traditional gongs that go round the movement only once. And two tourbillons are always better than one.
In their continual quest to build better watches, watchmakers have not only toyed with the concept that having additional critical components would improve performance, but they have also boldly acted on it, producing some of the most exciting mechanical movements in modern watchmaking history.
Oscillator is to watch what pendulum is to clock. A staggering majority of mechanical movements, whether made today or historically, have been designed with a single oscillator placed at the end of the gear train. The oscillator generally consists of balance wheel and balance spring, and its job is to convert the linear flow of power coming from the mainspring into oscillations, hence the back and forth motion. With each oscillation, it dispenses power to the escape wheel in pulses and this is how a watch advances each second.
Unlike a clock, which sits immobile on a mantelpiece or mounted on the wall, a watch and its movement are constantly put through different positions on the wrist. Gravity’s effect acts on the hairspring from as many as six different directions.
The argument that a tourbillon would be the ideal solution to optimal rate accuracy (or not) is a tale as old as time. A less conventional but no less exciting solution is to implement additional balance wheels instead of just the one.
Companies like Roger Dubuis, F.P. Journe, and more recently, Audemars Piguet and Greubel Forsey all have stunning inventions to show. In particular, Roger Dubuis outdid even itself and worked with two pairs of two balances in pursuit of timekeeping precision. Even ultra-niche MB&F has thrown its hat in the ring with this formula.
Audemars Piguet presented the Royal Oak Double Balance Wheel Openworked this year. It is the first timepiece by the Le Brassus manufacture to be made with two balance wheels, in what it calls the dual balance patented geometry.
Before this seminal invention, Audemars Piguet had only produced watches with double hairsprings. With the ambition to increase timekeeping precision, its watchmakers mounted a second balance wheel with its own balance spring on the same axis as the first, resulting in a regulator that oscillates at three hertz with double the mass. More mass equals more inertia, and more inertia enables the regulator to continue oscillating even when there is shock. Ergo, the greater the inertia, the more stable the timekeeping.
Precision also stands to benefit and this movement, Calibre 3132, boasts an average daily rate of -2/+10. Also, because the two balance wheels are set against each other, the hairsprings take turns to “breathe” and the effect of gravity gets cancelled out as the device regulates itself.
Greubel Forsey has always dabbled in movements with multiple balance wheels or multiple tourbillons set at multiple axes. From the get-go, this ultra-niche firm has been about modern horological inventions, and so it’s not surprising that it is home to the most robust collection of double (and quadruple) tourbillons on the market.
Joining the Double Balancier Incliné of 2009 is the breath-taking Double Balancier à Différentiel Constant with two balance wheels set at a 30-degree incline from the mainplate. Between two regulators lies a spherical and constant force differential that is used to average out the errors of the two balances. Note that because they’re set at an incline, the balances are already more accurate than ordinary ones, as no matter what position the watch is in, either one or both of the balances will not be completely vertical to the force of gravity.
Other than to even out the margins of errors of the two balances, the differential is also boosted by a constant force mechanism that sends energy in regular pulses to the two escapements. This means that irrespective of the movement’s state of wind, the amount of power being sent to the regulators remain constant.
Without it, the regulators stand to oscillate faster and stronger when the mainspring is fully wound, and with progressively less speed and power as energy in the mainspring depletes. Oscillating in tandem, the two balance wheels produce a hypnotic effect that is even more exciting to watch than any traditional high complication.
Going by the kind of watches Roger Dubuis has been producing, audacity would clearly be its middle name if the Genevan manufacture had one. Three years ago, it released a watch called the Excalibur Quatuor that had not one, not two, but four spring balances. Needless to say, the movement, Calibre RD101, stood beside itself both in terms of technique and aesthetic.
Each of the four balance wheels was set at an incline to average out the effects of gravity on the movement, and the wheels work in pairs, compensating immediately for rate variations caused by changes in position. According to Roger Dubuis, what the tourbillon achieves in 60 seconds, the Quatuor does instantaneously.
This movement is also equipped with a differential device to average out the errors of both pairs of spring balances, and oscillating at four hertz each, they come together to bring the accuracy of the movement to an astonishing 16 hertz. Putting one’s ear next to the watch, the break-neck speed at which all four balances simultaneously oscillate produces a sound that’s not quite the soothing, traditional tick-ticking, but rather, an almost deafening trill not unlike the cacophonous chirping of crickets.
A sure sight for sore eyes, the MB&F Legacy Machine No. 2 offers a sleek and modern take on the double balance movement. Ironically, though, this timepiece finds more inspiration in the past as opposed to the future. According to MB&F founder, Maximilian Büsser, the idea for the LM2 came from timepieces made by two esteemed watchmaking legends: the double balance calibres made by Ferdinand Berthoud from the 18th century and the one-and-only Philippe Dufour Duality.
Hovering above the dial, the two balances are supported by a pair of curved arms designed to evoke a distinctive futuristic vibe echoed by the bridge supporting the gilded differential wheel. The objective of this differential wheel is, once again, to average out the errors between the two balances. Oscillating at a leisurely 18,000vph, these mesmerising devices mirror each other and reflect the twin wheel layout of two gear wheels seen from the case back, which remind one of a style of watchmaking that was dear to Berthoud. Done, as usual, in collaboration with friends of the brand, the LM2 movement was designed by Jean-François Mojon of the movement specialist firm, Chronode, and expertly finished by Kari Voutilainen.
Making a movement with two balance wheels isn’t as easy as it sounds. Bear in mind that in watchmaking, as with all kinds of engineering, having more parts means more parameters to control. Therefore, a double balance movement is more than twice as complicated to make. In lieu of a differential to even out the performances of both balances, F.P. Journe utilised the much under-explored physical phenomenon known as resonance to synchronize the two balances.
Mechanical resonance is where the frequency of oscillation of an object matches the frequency of another, resulting in an increase of amplitude. The F.P. Journe Chronomètre à Résonance is, till date, the only wristwatch that relies on the resonance phenomenon for precision – proof that such a movement is immensely complex to design and difficult to achieve. Both balances have to be placed at the optimum distance from each other, and this is adjustable by a central pinion. Because they’re placed so near each other, one affects the other’s frequency, thus constantly compensating for the deviations. The two balances are also made in the signature F.P. Journe extra-large geometry with four arms and corresponding adjustable inertia weights, where large balance wheels typically offer greater stability thanks to higher moments of inertia generated.
Another area where an additional balance wheel comes in extra handy is in chronograph movements. Traditionally, chronographs experience a sharp drop in amplitude whenever the stopwatch mechanism is activated because those components deplete power from the gear train. Thus, for that split second or so, timekeeping precision would suffer, and fully regain only when the chronograph is stopped and reset. This condition affects not only chronographs, but all movements with additional functions, particularly functions that require a significant amount of power to operate. Repeaters are another example.
Having a separate balance wheel for the chronograph function not only eliminates this problem but also enables the movement to measure time autonomously and with even greater accuracy. When it is no longer at the mercy of the gear train, the chronograph’s balance has the freedom to oscillate at higher frequencies than the regular balance wheel.
This brings with it several advantages. The higher the frequency, the more accurate the timekeeper. Yet high frequency balances are subject to a lot more wear and tear, so limiting its use to only when needed would be extremely judicious. Finally, a high frequency balance needs to be small in diameter, which although fast and accurate, is not especially stable; large balances are stable although not as accurate. Therefore, what is the optimal geometry for good chronograph activity isn’t at all good for the regular hours and minutes, and so having a dedicated balance to each is to have the best of both worlds.
For a time, TAG Heuer had committed itself to the development of some of the fastest, most accurate chronographs on the market. Watches like the Carrera Mikrograph and Carrera Mikrotimer Flying 1000 offer super accurate chronograph function on the one hand and stable timekeeping on the other. The Mikrograph’s chronograph records time accurate to the nearest 100th of a second with a micro balance wheel that beats at an insane 360,000vph while the main balance wheel for the hours and minutes cruises along at a relatively leisurely 28,800vph, which is actually considered pretty fast for the hours and minutes.
On the other hand, the Mikrotimer Flying 1000 takes things up another notch, measuring time to the nearest 1,000th of a second. Its micro balance wheel powers on at a breakneck speed of 3.6 million times per hour, making it 125 times faster than a standard Swiss chronograph, and a hundred times more accurate than the most prevalent industrialized fast-beat chronograph movement, the Zenith El Primero. To watch this timepiece in action is not for the faint hearted because the central seconds hand spins around the dial a whopping 10 times per second. The only drawback is that the chronograph is only able to clock short events of no more than 150 seconds.
Both the Mikrograph and Mikrotimer Flying 1000 are made with the TAG Heuer dual-chain architecture, which eliminates the need for a clutch, but more impressively, both timepieces received COSC certification. Even while the chronograph is running, the watches remain highly precise.
Also measuring time in high definition is Montblanc with its TimeWriter II Chronographe Bi-Fréquence 1000 released in 2012. Again, there is one balance wheel for timekeeping and another for the chronograph, where the former beats at a deliberate pace of 18,000vph or 2.5 hertz, while in stark contrast, the latter pulsates at 360,000vph or 50 hertz. Here’s where the ingenuity of independent watchmaker Bartomeu Gomila comes into play.
Compared to the Mikrotimer Flying 1000’s 3.6 million vph frequency, the Bi-Fréquence 1000 is 10 times slower. Yet it manages to display time just as accurately (to the nearest thousandth of a second) thanks to Gomila’s unique and patented mechanism. According to Montblanc, it took 10 years for Gomila to build the prototype, which is based on the idea of a childhood game involving a hoop and a stick. Using a thousandths wheel as the hoop and the chronograph gear train as the stick, the thousandths wheel rotates 10 times per second with each impulse received from the gear train. Thus, Gomila’s invention allows further division of the elapsed time by 10 times, thus yielding 1/1,000th of a second reading from a 1/100th of a second balance frequency.
The chronograph also has its own mainspring and can continue running for 45 minutes when fully wound. Both balance wheels can be seen through the dial, along with the chronograph minutes and seconds at six o’clock, the centrally mounted hundredths of a seconds hand that corresponds to the scale on the outermost circumference, and an arch window at 12 o’clock displaying 1/1,000th of a second.
If there were just one watch that deserves to be made with two balance wheels, it would be none other than the Breguet Tradition. Firstly, this timepiece inspired by early Breguet souscription watches is known for its fully openworked aesthetic, where the balance wheel is mirrored by the third wheel and its arbour to form a pleasantly symmetrical aesthetic. But where the balance wheel can be seen constantly oscillating, the third wheel appears not to move at all, even though in reality it is – just very slowly. As beautiful as the Tradition is, many purists and WISes lament this one tiny imperfection.
With the Tradition 7077 Chronograph Independent, however, this “wrong” is finally righted, as instead of the third wheel, there is the chronograph balance wheel. To achieve maximum design integrity, Breguet made this balance wheel in the same size as the timekeeping balance. However, in order for it to function optimally, it had to be made in titanium. This is because it oscillates at five hertz and this needs to be lighter than the traditional timekeeping balance oscillating at three hertz.
It may not be ultra-precise like the TAG Heuer and the Montblanc but this timepiece is extra reliable as a pair of brakes engages the chronograph balance every time it starts and stops. Mainly, its role is to ensure positional integrity when the balance stops and optimal amplitude when it starts. Breguet has also used silicon overcoil hairsprings and pallet forks in these areas.
The chronograph can run continuously for 20 minutes because it has its own mainspring. Winding it isn’t done through the crown, but rather, it happens automatically when the reset button is pushed. The reset button winds a small blade spring, which can be seen through the sapphire case back.
Apart from introducing additional balance wheels, some watchmakers have considered other means of isolating a movement’s timekeeping elements from its functional ones. The most prolific of them would have to be Jaeger-LeCoultre and its ingenious Dual Wing concept. Introduced in 2008, it is essentially a system with two separate gear trains, each with its own mainspring and barrel, and both sharing one regulating organ.
As with double balance movements, one of the gear trains is dedicated to timekeeping and the other, all the functions and complications built into the movement. To date, they include moon phases, dual time, chronograph, the Jaeger-LeCoultre patented Sphérotourbillon, and the grande sonnerie in the inimitable Hybris Mechanica à Grande Sonnerie.
With a balance frequency of 21,600vph, the Jaeger-LeCoultre Duomètre watches aren’t the fastest timekeepers on the market but in terms of rate precision there is no doubt that they’re among the very best. Reaching -1/+6 seconds per day, the Dual Wing construction allows all manner of complications to function without causing any loss of amplitude to the balance.
This is because there is no connection between the two going trains; the two gear trains run completely independently of each other, that is, until the end where they converge at the balance wheel. Of all the variations made to date, energy guzzlers like the chronograph and the Hybris Mechanica à Grande Sonnerie stand to benefit the most from the Dual Wing construction.
Manually wound, the Calibre 380 movement family stays powered for 50 hours. This applies to the hours and minutes as well as the complication, in the case of Calibre 380A, the chronograph. Each barrel is clearly labelled and they correspond to their respective power reserve indicators on either side of the foudroyante counter displaying 1/6th of a second.
Hot on the heels of the Duomètre is the F.P. Journe Centigraphe Souveraine, which also offers a method of chronograph timekeeping that does not sap the life out of the mainspring, not even for a fraction of a second. Again, the chronograph has been isolated from the timekeeping mechanism, but here is where the Centigraphe Souverain is absolutely unique.
The hands of the 100th of a second, the 20 seconds, and the 10 minutes counters are driven by two different wheel trains bifurcated from the chronograph gear train. Next, the one-second and 20-seconds counters are also driven by their own wheel trains positioned on either side of a single intermediate wheel driven by the barrel arbour. Finally, yet another separate train of wheels, also driven by the barrel arbour, drives the 10-minutes hands. In short, all of the hands draw power directly from the mainspring.
To average out the effects of gravity on the balance spring, a watchmaker may decide to construct a tourbillon carriage with which to protect the balance wheel and its spring, but this device makes regulation exponentially more difficult. Said watchmaker may also decide to split the flow of power into two sets of balance wheel and spring, interpolating their rates of precision with a differential, as seen with the timepieces discussed earlier by Audemars Piguet, Greubel Forsey, Roger Dubuis, and MB&F.
While not quite as magnificent as the tourbillon, double balances are, in their own way, just as thrilling to admire. This places movements with double hairsprings one rung below the double balance when it comes to horological greatness.
Yet, it would not be fair to presume that such movements are inherently less complicated to make. The balance spring, a thing of beauty in itself, is something literally only a handful of watch companies can make in-house. To produce variants of the industry standard – Nivarox with Breguet overcoil – would be to call on a wholly different area of watchmaking expertise. At first blush, a double spiral looks deceptive simple, as it lacks the drama and fanfare of a tourbillon or a double balance system, but put it under the loupe and its beauty instantly becomes palpable.
How does a double spiral system resist gravitational forces? Positioned opposite each other, the springs “breathe” alternately; when one expands, the other contracts. In addition, they each move in the opposite direction. So, when the center of gravity of the first balance spring makes a shift, the center of gravity of the second one moves in the exact opposite direction, thus compensating for the error and ensuring that the gravity center is always kept at the center of the balance wheel.
The theory behind achieving optimal rate accuracy using two spirals is not too different from that which uses two balances – components move in opposite directions to equal out the effect of gravity on the spirals. But having two spirals in one balance wheel reduces the need for additional components, thus making it easier to regulate the oscillator.
Before this year’s Royal Oak Double Balance Wheel Openworked, Audemars Piguet has presented timepieces with two spirals within a single balance wheel. The Millenary Minute Repeater with AP Escapement combines the proprietary AP escapement with a double spiral (flat terminal curve) and variable inertia balance wheel that oscillates at 21,600vph. Its vast expanse of a dial affords stunning views of the escapement as well as the regulator.
Likewise, the Millenary Quadriennium also boasts the AP escapement and a double spiral regulator oscillating at 21,600vph. According to Audemars Piguet, the movements are as precise as a tourbillon, since the AP escapement brings higher timekeeping efficiency and the double spiral compensates for potential poising flaws. While flat spirals typically do not breathe as concentrically as overcoil spirals, a double spiral construct renders this issue void because errors are effectively cancelled out when the springs take turns to breathe and in opposing directions.
The production of hairsprings is a regular milieu of a very select few watchmaking companies. There is literally only a handful of them, and H. Moser & Cie. might be considered the least likely to boast this capability on account of its ultra-niche branding and small production numbers. Its sister company, Precision Engineering AG, makes balance springs that are physically comparable to the Nivarox springs invented by Reinhard Straumann, which almost all companies today use. Nivarox consists of about 45 per cent cobalt, 20 per cent nickel, 20 per cent chromium, five per cent iron, and smaller percentages of titanium and beryllium, and so does the Straumann hairspring proprietary to H. Moser & Cie., so named in tribute to the inventor.
Using two Straumann hairsprings, H. Moser & Cie. made a double spiral for the escapement in a timepiece that paid tribute to its founding father, Heinrich Moser. Rather than a flat hairspring, the spiral is made with a Breguet overcoil to allow optimal concentric breathing, and like all H. Moser & Cie. watches, its entire escapement can be removed from the movement thanks to the interchangeable module design. The escape wheel and pallet fork are done in hardened gold, another key characteristic of an H. Moser & Cie. timepiece.
Speaking of in-house manufactured hairsprings, Montblanc not only produces them by hand at its Villeret manufacture, but it also managed to flaunt this exceptional mastery with a double cylindrical spiral in the Tourbillon Bi-Cylindrique. Introduced in 2011, this timepiece is linked to historical marine chronometers, which also tended to be made with cylindrical hairsprings. In this work of mechanical showmanship, the double cylindrical hairspring is paired with an extra-large variable inertia regulator balance wheel and a magnificent tourbillon carriage that is essentially three infinity signs fused in one. The tourbillon bridge also follows through with the infinity symbol motif.
Where there is a double hairspring that already works to cancel out the effects of gravity, a tourbillon regulator is arguably superfluous. However, the Tourbillon Bi-Cylindrique stubbornly combines both in this showpiece that offers a mere hint of watchmaking savoir-faire by Montblanc’s Villeret manufacture. The oscillator moves at a frequency of 2.5 hertz or 18,000vph, which is the traditional speed of all of Montblanc’s Villeret-made timepieces. Slow compared to even moderately paced movements, the manual-winding Calibre MB M65.63 was intentionally given this frequency so collectors could clearly admire the beauty of the spirals, the balance, and of course, the tourbillon.
Who else also made a tourbillon with two spirals? Watchmaking independent Laurent Ferrier, which is known for its pure, understated designs that juxtapose with elaborately finished and decorated movements. In the Galet Classic Tourbillon Double Spiral, the balance wheel oscillates with two inverted hairsprings that are mounted at the center. Once again, the double hairsprings increase the reliability of the regulating system by neutralizing the lateral displacement of the balance axis. At a frequency of 21,600vph, the entire regulating system is housed within a gorgeously finished tourbillon carriage. In addition, it rotates once every 60 seconds under a hand-decorated and hand-finished tourbillon bridge.
In their perpetual quest for timekeeping precision, watchmakers never fail to turn up new inventions that surprise and delight. This is where watchmaking becomes an art, not just a by-product of physics and mathematics in time telling. The beauty of two balance wheels oscillating to a classical cadence, the dance of two hairsprings taking turns to breathe, the elegance of two tourbillons rotating in unison… Less is not always more, especially in high watchmaking.
This article was first published in WOW.