Automatic movements changed the landscape of watches and watchmaking, and most mechanical calibers have automatic winding rotors today. They’re certainly convenient, allowing active wearers to maintain a full reserve without a second thought. The technology goes back to the late 18th century when legends like Abraham-Louis Breguet attempted early designs that were promising yet impractical. His barrel remontoire, for example, was just too complex and expensive, while other designs like oscillating weights that moved up and down lacked the efficiency of today’s rotors. These were the days of pocket watches and automatic movements remained a rarity until the popularity of wristwatches took hold in the early 20th century.
Source: Fratello Watches One of five known examples of the earliest central-rotor watch movements, circa 1780. Image credit: watkinsr.id.au
Rethinking a Proven Design
There are a couple of issues with automatic movements, although they’re generally aesthetic complaints over engineering shortcomings. With a centralized rotor covering half of the movement, complex and decorated portions are visually blocked. Added bulk is also a consequence of the rotor hovering over a base caliber. A micro-rotor solves both of these problems, allowing almost the entirety of a movement to be seen while also substantially reducing thickness. Micro-rotors themselves are much smaller than conventional rotors and integrate into the movement in an offset location. A rear sub-dial if you will. They’re more difficult to design and perfect than conventional automatics, but the aesthetic advantages are significant. A major hurdle has been efficiency as smaller rotors have lower rotational inertia, making it harder to wind the mainspring. Heavy, dense metals are required to add adequate weight to the micro-rotor, such as gold, platinum or tungsten. Improved tolerances, bearings, and other technical advances have made today’s micro-rotors very efficient, almost on the same level as their conventional brothers.
Eterna Cal. 1198 a first to use the ball bearing mounted rotor. Source: Time and Watches
Horage K1 Automatic with centralized tungsten uni-directional rotor mounted on the exterior of the movement. Rotors can take up more space and have weight distributed over a flatter plane.
K2 Micro-Rotor - an inset rotor creates a lower profile but relies on maximizing rotor thickness and density.
Birth of the New Automatic
The micro-rotor first appeared in 1958, coming from two different companies that developed them separately yet simultaneously – Universal Geneve and Büren. Hans Kocher, Chief Design Engineer at Büren, referred to the design as “Planetary” as the smaller rotor resembled a planetary gear. Universal Geneve called their design “Microtor,” which was 4.2mm thick compared to Büren’s 4.15mm.
Büren Planetary Calibre 1006 - Source: Armbanduhren.de
Universal Geneve Microtor- Source: Armbanduhren.de
A year later, Piaget shocked the industry with the Caliber 12P at only 2.3mm, which held a thinness record for several decades. Piaget’s micro-rotor was celebrated as the thinnest automatic movement at the 1960 Basel Fair, which consequently led to the thinnest automatic watch.
Piaget Calibre 12P - Source: Armbanduhren.de
Büren and Universal Geneve didn’t rest on their laurels, designing movements that became more competitive within a few years. Büren’s Intramatic in 1962 was 3.15mm and the 1964 Intramatic Caliber 1321 was only 2.85mm. In 1969, the Büren Chronomatic Caliber 1281 was used in the first micro-rotor chronograph. As promising as the designs were, they remained expensive and rare luxuries compared to the tried and true standard autos. This basically holds true today.
Mainstream Luxury
Patek Philippe created what’s arguably the most legendary micro-rotor movement in 1977 with the Caliber 240, which debuted in the Golden Ellipse 3738 watch. It’s not the thinnest micro-rotor movement at 2.53mm, but still ultra-thin and thinner than the brand’s hand-wound Caliber 215 at 2.55mm. Tweaked and perfected over the decades, it remains an active Patek caliber today and an icon in the industry.
Calibre 240 1977 to present - Source: Deployant
Vaucher Manufacture Fleurier isn’t a watch brand per se, but among the most well respected, high-end Swiss movement manufacturers that supply micro-rotor calibers (and many others) to third parties. It has a considerable 35,000 units per year. Audemars Piguet, Richard Mille, Corum and Parmigiani Fleurier are just a few of Vaucher’s prestigious clients. Their SEED VMF 5401 micro-rotor is only 2.6mm thick and comes in many varieties, from time only to skeletonized with multiple complications to a full perpetual calendar, and brands are often free to rename them for their own luxury portfolios. It’s quite an offering.
Parmigiani Fleurier Tonda 1950 based on the Vaucher 5400 series - Source Monochrome Watches
But even today, not many watchmakers use micro-rotor calibers as they’re again expensive and more difficult to produce, but notable brands that do include Patek Philippe, A. Lange & Söhne, Czapek, Bvlgari and Parmigiani Fleurier (Vaucher is the sole movement manufacturer for Parmigiani Fleurier). All of the above, of course, are high-end luxury brands. Many have found great success with these calibers, such as Bvlgari with the Octo Finissimo that has the thinnest automatic (micro-rotor) movement at 2.23mm with the Caliber BLV138. This is the one that finally beat Piaget’s Caliber 12P. Bvlgari also has a perpetual calendar micro-rotor at only 2.75mm. Neither would be possible without an integrated micro-rotor as a central counterpart would add 1mm or more in thickness.
Horage K2 Micro-Rotor and the Competition
The K2 micro-rotor powering our Supersede all-terrain sports watch brings significant developments and innovations to the table. The function and profile for the Suprsede calibre is 3.6mm, however K2 comes in both a 2.9mm and 3.3mm profile. 3.6mm was required as Supersede comes with multiple complications that include a GMT and day/night indicator, power reserve indicator and date. The movement is modular with 38 possible variants via the three different profiles.
How does this compare to luxury calibers from Switzerland and Europe?
Let’s take a quick look at some K2 specifications and see how they hold up to the likes of Patek Philippe, A. Lange & Söhne and Bvlgari.
• 2.9mm - Small Second or Centre Three Hands.
• 3.3mm - Small Second or Centre Three Hands and Calendar.
• 3.6mm (Supersede Profile) - GMT, 12/24 hour day/night Indicator, Power Reserve Indicator, Calendar and Small Seconds or Centre Three Hands.
• 30mm diameter
• 23 jewels and 3.5Hz frequency (25,200vph)
• 72-hour power reserve
• Micro-rotor is currently gold plated tungsten
• Chronometer level of accuracy at -4/+6 seconds per day
• Silicon escapement and hairspring (light, wear/temperature resistant and anti-magnetic)
• Supersede is under 10mm at 9.85mm in height
• Supersede retail price – CHF 6,500 (early bird pre-order price of CHF 4,900)
Patek Philippe Golden Ellipse (ref. 5738R) – CHF 27,200.
This is a time-only piece with the Caliber 240 micro-rotor in a rose gold case. Patek is a member of the Holy Trinity, so we’re talking about the top echelon. The movement is 2.53mm in height and the case is very slim at 5.9mm, although there are no complications and not even a seconds hand. The power reserve is 48 hours compared to 72 hours on the K2 and it beats at 3Hz compared to 3.5Hz. The rotor’s weight comes from 22k gold. Accuracy isn’t specifically listed, but I’m sure it’s at a chronometer level. The Caliber 240 is thinner than K2's 2.9mm due likely to having no small seconds complication, it is however elegantly decorated. A great example of the market positioning at the top end of the spectrum for a time only function on a Swiss micro-rotor.
Ref: 5738R - Source Hodinkee
Calibre 240 - Source: Hodinkee
Parmigiani Fleurier Tonda PF Micro-Rotor Steel – CHF 21,000.
This is a time and date only piece with Vaucher’s Caliber PF703. The rotor’s weight comes from platinum this time, effective yet expensive. It’s 3mm in height, allowing the case to be 7.8mm and it has a 48-hour power reserve. It’s a well finished piece, but more time spent on engineering might have increased its relatively low power reserve and might have allowed for an escapement upgrade to silicon.
Source: Deployant
You get the idea of how these ultra-luxury micro-rotors are positioned in the market. Intricately hand finished with precious metals, but often lacking in features and complications with price a topic of debate. Below are a few additional examples from Bvlgari, A. Lange & Söhne and Czapek.
Bvlgari Octo Finissimo – USD 12,200
2.23mm in height (6.4mm case), 3Hz frequency, time-only with small seconds, platinum rotor, 60-hour power reserve.
Source: Monochrome Watches
A. Lange & Söhne Saxonia Annual Calendar – CHF 53,500.
5.4mm in height (9.8mm case), 3Hz frequency, annual calendar, big date and moonphase, 21k gold rotor, 48-hour power reserve.
A look at the micro-rotor on the A. Lange & Söhne Saxonia Annual Calendar - Source: Hodinkee
Czapek Antarctique – CHF 18,000.
4.2mm in height (10.6mm case), 4Hz frequency, time and date only, platinum rotor, 60-hour power reserve.
Czapek Antarctique - Source: Hodinkee
Looking at the specs and finish of K2 compared to its luxury peers, it often has more complications and possible configurations. In addition, it’s well finished and on full display behind a sapphire crystal. This starts with black gold plating and yellow gold lettering, giving it a unique, stealthy aesthetic. Then there’s Côtes de Genève on the main bridge, anglage edging, brushing and key cutouts that show deeper areas of the movement. All techniques are hand finished. Many of the 23 jewels also contrast well against the black caliber, adding to the overall presentation. Horage is proud to be positioned so competitively amongst the leaders in micro-rotor development. A price of 6,500 CHF is one thing, but the combination of function, performance and aesthetic Supersede is quite literally in a league of its own.
Optimal Beat Rate and Power Reserve
Price, thinness and finishing are important, but frequency (beat rate) is vital to overall performance. It really sets the tone on both accuracy and power reserve, and what can be achieved with a single barrel. There are three common beat rates with automatic movements – 3Hz, 3.5Hz and 4Hz. The lower the beat rate, the higher the possible power reserve, but accuracy can suffer in many cases. A higher beat rate of 4Hz (or 5Hz in some cases) increases accuracy, but consequently reduces the power reserve. Horage hits an optimal middle ground throughout its entire portfolio with 3.5Hz (25,200 beats per hour), which allows for a chronometer level of accuracy (-4/+6 seconds per day) and a 72-hour power reserve for K2. That's three full days.
**Update to the above. A higher beat rate in steel escapements can increase accuracy. A lower beat rate when engineered well and when a silicon escapement is used has incredible precision. We have found 3.5Hz as the optimal beat rate to provide sufficient power reserve savings and by using silicon there our engineers have found no precision advantages to beat rates of 4Hz or more.
Engineering around a target frequency to achieve the desired efficiency, accuracy and thinness is challenging to say the least. We’re again not trying to create the thinnest movement in the world, but our focus is on performance. To us performance means chronometer level accuracy, high efficiency with the ability to generate at least a 3 day power reserve and competitive in dimensions that allow a case to be under 10mm in thickness. K2 achieves this with a higher power reserve via a single barrel than much of the competition, while adhering to the strict COSC standards of accuracy.
Power Reserve Generation
An often overlooked (or intentionally unspoken) specification is efficiency in relation to power reserve generation. It's one thing to have an impressive power reserve, especially via one barrel, but what about a micro-rotor's ability to generate that reserve? Many brands, including the most prestigious, leave this information on the cutting room floor as they have less than optimal efficiency in this area. It's harder for a smaller rotor to wind the mainspring compared to its centrally mounted counterpart, even with heavy and expensive metals like platinum. Horage has achieved an efficiency that's impressive even by conventional automatic standards and we're proud to share it. We've calculated that one hour on the wrist generates 10 hours of power reserve, so an unwound K2 can be fully charged in less than eight hours on the wrist. Of course, wear it regularly and you'll never have to worry about running out of gas (even if you leave it on your dresser over the weekend).
Silicon and Isochronism
We have silicon escapements in all of our movements, but the K2 takes it further. The hairspring will be silicon as well, which was restricted to a small handful of watchmakers such as Patek Philippe, Rolex, Ulysse Nardin and the Swatch Group due to patents. With many expiring in 2022, we're adding a silicon hairspring to K2 for our 2022 production.
Isochronism, or the consistency or uniformity of frequency, is higher with silicon components as they're anti-magnetic and resistant to negative influences of temperature fluctuations. Silicon is also much lighter and more resistant to wear, requiring less lubrication. A silicon hairspring will help ensure maximum consistency of the balance wheel as it's also immune to temperature and magnetic influences. This means that a movements accuracy is far less effected by beat rate. We have found that 3.5Hz is the optimal beat rate with silicon and there are no distinguishable advantages when going to 4Hz.
It's Time for Micro-Rotors to Take Center Stage
Micro-rotor calibers have reached a point where they can step out of the shadow of their conventional counterparts. Piaget’s Caliber 12P demonstrated how thin and “exotic” an automatic could be over 60 years ago, while Bvlgari’s Caliber BLV138 pushed things even further. Patek Philippe really set a standard in the late 70s with the iconic Caliber 240 that remains in their stable after more than four decades. Today’s micro-rotors are a culmination of this and more – they’re well proven, very efficient and notwithstanding the rarely seen peripheral rotor, aesthetically superior to standard automatics. The K2 was designed and engineered entirely by our exceptionally talented watchmakers and engineers, and clearly demonstrate how Swiss micro-rotor movements can be affordable while also being accurate to a chronometer level, very efficient and able to hold a sizeable power reserve. Don't forget about our silicon escapement and hairspring, the latter being a rarity and almost always reserved for a few well established luxury brands.
Horage is ready to take the lead with a new generation of accessible Swiss micro-rotors, not unlike what we did with the unprecedented K-TOU Tourbillon. Our focus is always on quality, innovation and consumer trust, without artificial inflation and red tape from parent companies. It’s what we do as an independent performance watchmaker.
What's your take on the micro-rotor?
Is it the future automatic platform?
Let us know in the comments.
Written by Erik Slaven
Rotor and winder efficiency also depends on breaking and friction control on the mainspring. Is Horage doing anything new on the mainspring friction clutch?
Wow - fascinating that unidirectional in real word is more efficient! I love the meticulous engineering focus the Horage team has and the fact you share these intricate findings and observations with the community — it drives a lot more excitement on my end
Informative as always - learned something new with Parmigiani Fleurier. Out of curiosity more than anything, I wonder what the "wear to wound time" is on the other pieces referenced in the article. With people potentially rotating watches, it's an insightful practical statistic
I found this an interesting and informative article which usefully positions the splendid product developments taking place at Horage
I like the K2 for its silicon freesprung balance. My other silicon spring watch has amazing isochonism. That is the key to high power reserve. It holds a good rate over a wide torque range.
I do not have a strong desire for a reserve of much more than 24 hours if the watch has a quick set date and hacking. It is easy enough to set it up when I wnat to wear it and I prefer it not running much if I am not wearing it. It's done, but my preference is for 4Hz or 5Hz and less reserve.
I would like to read more about the silicon escapement parts. The classic high end levers and escape wheels were fabulous. How is the lubrication at the teeth held? Is is equi-angular equidistant semi or some new idea?
Superlative engineering!