Precision Engineering AG brings back 18th century invention in presentation of its first cylindrical hairspring


First invented by English watchmaker John Arnold in 1776, Precision Engineering AG has shown off its first prototype of the cylindrical hairspring, in Palexpo, Geneva.

At the EPHJ show, taking place from June 12-15, Precision Engineering AG presented the prototype of its first cylindrical hairspring which aims to improve isochronism in a watch mechanism.

With a history that spans across four centuries, the cylindrical hairspring is reminiscent of an endless screw or a corkscrew as it rises perpendicularly around the upper stem of the balance spindle.


Precision Engineering AG is a specialist in developing, producing and assembling component elements for regulating organs as achieving isochronism on the spring balance is one of the main goals for watchmakers.

With a flat hairspring, the opening is not concentric and leads to friction due to movement of the centre of gravity, which as a result disrupts the isochronism.

It is with this in mind that Precision Engineering AG decided to take on a new challenge by developing a cylindrical hairspring which aims to enhance the isochronism.

The cylindrical hairspring was a frequent feature on marine chronometers in the 1700s as 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. This is despite Philips or Breguet terminal curves, which were specifically developed to partly correct the non-concentric opening of the hairspring.

It is thanks to the cylindrical hairspring, fitted with a Breguet curve attached at two points, that friction on the pivots is reduced and isochronism is improved.

However, due to its specific shape, the cylindrical hairspring requires more space which means it is also extremely difficult to produce, taking ten times longer than a traditional hairspring.

A cylindrical hairspring is designed for highly exclusive watches, produced in small numbers, or even for unique pieces.

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