Armin Strom System 78 Gravity Equal Force – part one

In this first of a two-part in-depth look at the Armin Strom System 78 Gravity Equal Force, Angus Davies goes behind the scenes and reveals some of the fascinating details relating to this technical tour de force.

Image – plate prior to eletroplating

For many years, those watch collectors with an innate mechanical curiosity have been drawn to the naked delights of ‘openworking’ or ‘skeletonising’. This technique involves removing material from an existing movement in order to reveal the splendour of numerous parts in motion.

A skilled artisan will remove surplus material with a hand saw, taking care not to compromise the intrinsic strength of the main plate and other components. Prior to using the handsaw, the artisan will consider the load bearing areas of the movement. He or she will avoid touching jewel beds, any screws or venturing near those areas where the gear train dwells.

When openworking a movement, the ultimate goal is to augment the aesthetic appeal of a watch by creating a near-transparent characteristic. However, only the most accomplished practitioners should undertake such work as the torsional rigidity can easily be lost and, by default, the reliability can be impaired.

The Armin Strom method

In 2009, Claude Greisler and Serge Michel opened the new Armin Strom Manufacture in Biel, a watchmaking haven in the canton of Bern. From the outset, the brand proclaimed to the world, ‘We show what we make’, creating a diverse collection of openworked watches.

However, while other brands often adapt off the peg watches when creating openworked timepieces, Armin Strom employs a very different method. Using state of the art CAD (Computer-aided design) systems, Claude Greisler and his team embrace a clean sheet design method, conceiving watches that are designed to be openworked from the outset.

This approach confers significant benefits. Firstly, it is less labour intensive than modifying an existing calibre. Secondly, it ensures product consistency and, finally, it allows the brand to calculate the forces acting on each element of the movement, thereby forgoing material only where viable.

The best analogy is to consider an open roof car. A car which is designed to be a convertible from the outset is likely to have superior torsional rigidity when contrasted with a hatchback modified into a cabriolet. Ideally the strength is located in those areas where the loads are greatest. By adopting this approach there is less flex in the body and chassis, enhancing driving pleasure. In terms of a watch movement, flex can lead to some components inadvertently touching others, impairing reliability.

On the face of it, everything would suggest the Armin Strom method is the obvious approach to take. However, for most practitioners of openworking, this technique is not feasible. Quite simply, few companies have the capacity to make their own bespoke main plates and bridges. Furthermore, few firms share the same technical competencies as Armin Strom.

A Manufacture par excellence

Watch brands tend to source components from specialist firms. Cases, dials and straps are just some of the components which watchmaking Maisons procure from third parties. Armin Strom is no exception to this rule, sometimes turning to those companies with the expertise to supply high quality parts.

However, while many watch brands use third party movements, Armin Strom produce all its own calibres, making the brand worthy of the denomination, ‘Manufacture’.

Image – T0 – main production area

To be a Manufacture is not for the faint-hearted. It requires significant capital investment and much technical expertise. Thankfully, Claude and Serge were able to fulfil these requirements. Moreover, the planned opening of their Manufacture was fortuitous. The watch industry was licking its wounds after the banking crisis of 2008 and certainly had no appetite for purchasing new plant. Potential machinery suppliers were eager to ‘do deals’ and Armin Strom acquired cutting-edge equipment at never to be repeated prices.

Image – CNC machine

The brand’s impressive asset register allows it to make an array of components. CNC (Computer Numerical Control) machines employ different tools to mill brass blanks (barquettes), creating plates and bridges to infinitesimal tolerances. These tolerances are usually 1 – 2 microns (a human hair typically measures 50-70 microns).

Image – profile turning machine

Profile turning machines are used to create screws, pinions, wheels and pivots. Wire erosion machines employ an electrified wire immersed in deionised water to cut steel components to even smaller tolerances than CNC machines. Armin Strom use this know-how for making levers and the company’s patented resonance clutch spring.

Image – wire erosion

Despite the widespread use of cutting-edge technology, micrometers are still widely used to ensure all components are made to specification. Nothing is left to chance.

Pushing the boundaries of watchmaking

Throughout its history, Armin Strom has always looked to ‘push the boundaries of watchmaking’. Like many practitioners of haute horlogerie, Armin Strom has made an array of tourbillons. The tourbillon, patented by Abraham-Louis Breguet in 1801, is designed to counter the adverse effects of gravity on the regulating organ, conferring greater precision.

Image – a selection of the many parts made at Armin Strom

However, Claude Greisler and his colleagues looked beyond the established horological norms and created a watch featuring two independent balances, linked with a patented resonance clutch spring. After a relatively short period of time, the two balances become synchronous. A resonance watch matches the precision of a tourbillon while offering superior stability (the consistency of the rate).

Earlier this year, the brand paired its resonance clutch spring with one of the oldest and most coveted complications, the minute repeater. However, not happy with a ‘simple’ minute repeater with circular, two-dimensional gongs, the Maison from Biel made a watch housing intricately shaped, three-dimensional gongs. The resultant watch, the Minute Repeater Resonance not only delivers an incredible degree of precision, but produces a rich chiming sequence unlike any other minute repeater. Once again, despite its tender years, Armin Strom has shown it is capable of making watches par excellence.

Armin Strom System 78 Gravity Equal Force

Image – plan for making the reduction wheel on the new Calibre ASB19

Now, the brand is about to unveil a new watch that casts aside convention and embraces ingenuity. The Armin Strom System 78 Gravity Equal Force is the latest innovative watch from the Bernese firm.

A consistent supply

When a mainspring is fully wound, it is likely to send excessive force to the escapement. Likewise, as the mainspring becomes relaxed, the force serving the escapement is often insufficient. Too much or too little force, adversely affect the balance’s amplitude and, by default, precision. Ideally, the force serving the escapement should be constant.

Various constant force systems have been produced over the years, including the fusée and chain system and the remontoire. While such systems are effective, they often prove expensive. Although Armin Strom is a high-end maker of watches, it wanted to create a highly effective method of modulating the force of the mainspring while offering its clients comparatively keen pricing. Moreover, the brand wanted a system that was not unduly bulky in order to ensure its watch exhibited modest proportions.

The Armin Strom System 78 Gravity Equal Force features a special barrel.

When the crown is rotated on a ‘standard watch’, energy is sent via the transmission wheel to the ratchet wheel. As the ratchet wheel turns, it tensions the inner part of the mainspring around the arbor, causing the arbor to rotate. Once winding is complete, the arbor remains fixed while the barrel housing rotates transferring energy to the centre wheel. In this case, the mainspring barrel doesn’t rotate in a precision jewel bearing but around the arbor, heightening friction and delivering an inconsistent supply of force.

Image – a schematic of the new Armin Strom barrel fitted to the Gravity Equal Force

However, on the Gravity Equal Force, the watch is fitted with a ‘motor barrel’. In this instance, the barrel housing remains locked after winding and the arbor transmits energy to the gear train. By adopting this approach the arbor is more stable, with less side to side motion, moving more precisely when driving the going train and mitigating wear.

Armin Strom System 78 Gravity Equal Force

Image – barrel cover

For the ‘first time a stop-works declutch mechanism has been added to an automatic winding movement.’ Historically, it has proved difficult for companies to pair a stop-works with a self-winding movement, however, Armin Strom has overcome various technical obstacles and succeeded in creating a reliable mechanism.

Armin Strom System 78 Gravity Equal Force

Image – model of Geneva wheel

The stop works comprises of a Geneva wheel with a number of teeth. It exhibits a different appearance to the often used ‘Maltese Cross’ and restricts the rotation of the mainspring barrel to just 9 full turns out of a possible 12½. This ‘represents the central 72% of the mainspring’s possible torque curve, the flattest and most consistent portion. As the barrel housing unwinds around the arbor, a pin counts off the rotations on the Geneva wheel until it reaches the locked position and prevents further winding.’

Armin Strom System 78 Gravity Equal Force

Image – Geneva wheel

It is this combination of the special barrel design and the Geneva wheel which ensures the power delivery to the regulating organ is as consistent as possible and the amplitude is within the optimal range.

Continuous improvement

Part of the Armin Strom paradigm is the desire to continuously improve its watches. This is manifest with the gear train wheels. For some time Armin Strom has endowed these wheels with involute teeth, enhancing the efficiency of the power transmission.

The company recently completed a 6 year research and development project, seeking to improve the efficiency of gears. Now, its latest gears, fitted to the Armin Strom System 78 Gravity Equal Force, feature newly designed involute teeth, delivering superior power transmission. Clearly, Armin Strom does not rest on its laurels, continually seeking advancement.


While Armin Strom is young and fresh, it has repeatedly demonstrated its impressive technical prowess and shown it is at the vanguard of haute horlogerie. The Biel-based firm embraces technology and frequently enjoys the creative freedom of being a ‘Manufacture’.

Image – perlage adorning a main plate

However, while the Swiss watch company creates exemplars of contemporary design, it does not shun traditional hand craftsmanship. Indeed, this is never more so than with the finissage employed on the new Armin Strom System 78 Gravity Equal Force. The widespread embellishment of surfaces on this latest watch will undoubtedly leave diehard purists impressed.

In my next feature, I look closely at each element of this groundbreaking timepiece which represents a new chapter in the company’s prodigious history.

Further reading

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