The balance spring is the small spring that regulates the rate of the watch. In conjunction with the balance wheel and the escapement, it ensures that the movement beats at the desired speed. This extraordinarily slender, light, fragile and decisive component is as crucial as it is discreet. What few realise is that it stems from several centuries of progress, and that countless brands and watchmakers have attempted to endow it with the most stable possible shape and composition – the overall aim being to ensure that the perpetual coiling-uncoiling sequence it is expected to perform should likewise remain as regular as possible, whatever the circumstances.
The balance spring comes in two main forms. The first is the flat balance spring, a configuration in which it is coiled like an Archimedean spiral. This version is used in cases that call for saving space or means, since it is both thinner and simpler to form.
The second more stable and efficient form is known as a balance spring with Phillips terminal curve. It is named after Edouard Phillips, the French mathematician who took an interest in horology during the 1860s. He formalized a principle previously discovered by Breguet. Modifying the shape of the end of the spring, by bending the outer coil and curving it above the rest of the coiled spring, serves to enhance its stability. This type of balance spring is nonetheless 95% flat, although other models featuring varying degrees of volume have existed in the past. Some were convoluted and others simply too complex to implement. They deliver certain benefits in terms of chronometry (precision timekeeping), but often to the detriment of cost effectiveness. There is only one brand that still produces several of these exceptional variations: Jaeger-LeCoultre.
No other brand offers so many different kinds of balance springs, naturally including the flat and Phillips terminal curve versions, but also a helical spring officially known as the cylindrical balance spring. This tube-shaped coil equips several tourbillon models including the Duomètre à Sphérotourbillon, on which it oscillates around its long vertical axis.
In launching the Gyrotourbillon 3, the brand presented a spherical balance spring. Hand-crafted to form a kind of ball, it naturally accompanies the 360° rotations of the tourbillon carriage equipping this superlative watch. Finally, for the Gyrotourbillon 4 (officially known as the Reverso Tribute Gyrotourbillon) Jaeger-LeCoultre presented a hemispherical tourbillon that is prestigious, exclusive but not as thick as the spherical one. It is therefore eminently suited to this watch of which one of the purposes it to slim down a three-dimensional tourbillon.
Jaeger-LeCoultre cultivates a number of skills, but not everyone knows that forming the balance spring is one of them. An all but forgotten art generally delegated to a specialised large-scale producer (Nivarox Far, a Swatch Group company), the balance spring has once again become a key issue in the watch industry for supply-related reasons. This led to renewed awareness of its importance and the extent to which it had been neglected despite the fact that it represents a significant piece of history and a very special form of know-how. Jaeger-LeCoultre has recaptured the delicate operations involved in this process and ensured their continuity in cooperation with A. Lange & Söhne, a brand that has been using its in-house balance springs for many years. The latter’s know-how was thus leveraged by the Richemont Group which owns the brand and which asked the sister brand from Le Sentier to assist in creating a balance spring production unit within ValFleurier, the group’s large in-house component and movement production facility. One could scarcely imagine a more strategic and sensitive move.
