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Precision Engineering’s first cylindrical balance...
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Precision Engineering’s first cylindrical balance spring

Thursday, 05 July 2018
By The FHH Journal editors
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The FHH Journal editors

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2 min read

Sister company to H. Moser & Cie, Precision Engineering is one of the few manufacturers with the capacity to develop and produce regulating organs and their components: balance springs, balances, levers and escape wheels. At last month’s EPHJ fair, it presented the prototype for its first cylindrical balance spring.

Achieving isochronism on the spring balance is one of the main goals for the watchmaker. With a flat hairspring, the opening is not concentric and leads to friction due to movement of the centre of gravity. As a result this disrupts the isochronism. Precision Engineering AG is continuously working to develop its expertise in order to provide its customers with products that are always high performing. It is with this in mind that the company decided to take on a new challenge by developing a cylindrical hairspring.

Cylindrical balance spring from Precision Engineering
Cylindrical balance spring from Precision Engineering

Invented in the 18th century by John Arnold, an English watchmaker, the cylindrical hairspring is reminiscent of an endless screw or a corkscrew. It rises perpendicularly around the upper stem of the balance spindle. A frequent feature on marine chronometers at the time, it offers the advantage of developing concentrically, and therefore geometrically, given that it works perfectly on the axis of its pivots, unlike the flat hairspring, whose opposite ends have a tendency to exert force on the pivots, despite Philips or Breguet terminal curves, which were specifically developed to partly correct the non-concentric opening of the hairspring. Thanks to the cylindrical hairspring, fitted with a Breguet curve attached at two points, friction on the pivots is reduced and isochronism is greatly improved.

In return, due its specific shape, the cylindrical hairspring requires more space. It is also extremely difficult to produce, taking ten times longer than a traditional hairspring. Very few companies have the expertise and skill required to be able to produce a hairspring like this. In order to rise to this technical challenge, Precision Engineering AG had to develop new tools and put new procedures in place. A cylindrical hairspring is designed for highly exclusive watches, produced in small numbers, or even for unique pieces.

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