The balance spring sets the pace

Without the spiral, there’s no regular ticking. No defined cadence or rhythm, let alone precision. If a watch is running late or early, the watchmaker will turn to it. It’s a heavy responsibility that weighs on the shoulders of this tiny component, barely thicker than a hair. Presented to the Royal Society in 1675 by Dutch mathematician and engineer Christiaan Huygens, the invention of the balance-spring revolutionized watchmakers’ quest for precision. Coupled with the balance wheel, whose constant oscillations it ensures thanks to its elasticity, it constitutes the watch’s regulating organ. In other words, its beating heart.

Since then, efforts to improve its performance have kept watchmakers’ R&D departments busy. Because in order to display flawless isochronism, winding and unwinding endlessly with the regularity of a metronome, the balance-spring must guard against numerous enemies. Shocks, of course, but also magnetism, terrestrial gravity and temperature variations. Watchmakers have come up with a number of solutions to counter their harmful effects.

Alloys…
The first is the composition of the alloy. In the early 20th century, Charles-Édouard Guillaume proposed an alternative to steel by creating Invar, an alloy of iron and 36% nickel. Its properties? Not very sensitive to magnetism, it also has the advantage of a very low coefficient of thermal expansion. For almost a century, balance springs were mainly made of Invar, Elinva (an alloy of steel, nickel, bromine and tungsten) or Nivarox (steel, nickel, cobalt, chromium and beryllium). It wasn’t until 2000 that silicon made its appearance in Ulysse Nardin’s Freak, before conquering a number of major watchmaking houses seduced by its qualities. In addition to its excellent resistance to magnetism, the silicon balance-spring has the advantage of being manufactured in the desired shape and length in a single step, offering a gain in watch reliability. The latest innovation comes in 2019 with the launch of a new nanocarbon balance spring. It took TAG Heuer several years of research to develop this ultra-light balance-spring, which is as non-magnetic as it is insensitive to the force of gravity and shocks.

… and shapes
In addition to the alloy, the shape of the balance-spring can have a significant impact on its performance. Alongside the traditional flat balance-spring, Jaeger-LeCoultre offers a variety of shapes, from cylindrical to domed. Another shape highly appreciated for its reliability is the one invented in 1795 by Abraham-Louis Breguet, who had the ingenious idea of raising its outer spiral according to a precisely calculated curve to ensure the concentric development of the balance-spring, the watch’s guarantee of precision. This technical feat is known as the “Breguet curve” or “Phillips curve” after the French mathematician Edouard Phillips, who perfected Breguet’s mechanism in the 1860s.

FALSE BROTHERS

Of the many components that make up a mechanical movement, only two are spring-shaped. If they have more or less the same shape, be careful not to confuse them. The spiral spring is the watch’s regulating organ. The barrel spring, on the other hand, delivers the energy the movement needs to function.