Thinner than a human hair, weighing just a few milligrams and indispensable to a working movement: hairsprings are among the most delicate components of a modern timepiece. They look back on a centuries-long history full of technical innovation and are still being refined today to maximize the precision of automatic watches. We explain the role of the hairspring in a movement, what matters in its manufacture and how cutting-edge methods keep improving this microscopic component.
The Road to Perfection – A History of the Hairspring
Mechanical watches get their periodic beat from the so-called balance-spring system, first developed in 1675 by the Dutch physicist Christiaan Huygens. He realized that the balance wheel can only reliably perform its function as a regulating organ when a hairspring, coiling and uncoiling concentrically, ensures an even rhythm. The sequence is always the same: an impulse sets the balance oscillating, after which the hairspring slows it down, pulls it back and swings it out in the opposite direction. The hairspring should not be confused with the so-called mainspring, which supplies the movement with its driving energy.
The hairsprings used in wristwatches are known as flat hairsprings, because both ends of their thin steel strip are fixed in a single plane, so they take up very little space. The famous Swiss watchmaker Abraham-Louis Breguet decisively improved this system around 1796 by raising the outermost coil of his hairsprings in a specially calculated curve. Thanks to this inconspicuous detail, the "Breguet overcoil" ran noticeably more precisely, and its basic principle is still in use today. From 1860 onward, later calculations by the French mathematician Eduard Phillips made it possible to design the physically perfect terminal curve. Yet another property of hairsprings would prove even more decisive: their material.
Material and Manufacturing: The Finest Details Make the Difference
After decades of research into the optimal composition of the tiny spring, the Swiss engineer and entrepreneur Reinhard Straumann finally achieved the breakthrough in 1931: his alloy "Nivarox," whose name stands for "non-variable, non-oxidizing," delivered the best precision figures to date. Although the approximate mix is common knowledge (in addition to iron, nickel and chromium, it also contains beryllium), the exact details of its composition are known only to the company Nivarox-FAR.
This Swatch subsidiary is by far the largest hairspring manufacturer in the entire watch industry.
But how is this tiny component actually produced? The process begins with a Nivarox wire about 0.5 mm thick, whose diameter is still worlds away from the size required for hairsprings. It is therefore drawn through a series of dies that strip away its outer layers until the diameter has shrunk to around ten percent of its original value. Uniformity is paramount: a deviation of just one thousandth of a millimeter is enough to render the wire unusable. Once the strip is finished, it is cut into precisely measured lengths, which are formed into a spiral using a winding block.
Subsequent heat treatment in a vacuum furnace gives the blanks additional stability. Before the hairsprings can be fitted into automatic watches, the terminal curve still has to be precisely bent. Sorting hairsprings and balance wheels into 20 classes allows the two components to be matched exactly – only if both parts belong to the same category can they be paired.
The Industry: Where Are These Delicate Springs Made?
Looking at the hairspring market, the almost overwhelming dominance of the aforementioned Nivarox-FAR stands out immediately: roughly 90 to 95 percent of all Swiss watchmakers source their components there. Compared with mainsprings, which are frequently made in-house, competition here is thus heavily monopolized. What sounds negative at first actually turns out to be a win-win situation: the company's high degree of specialization not only enables first-class product quality but also keeps prices low. Nevertheless, there are some examples of brands whose movements use hairsprings from their own production.
Rolex in particular has proven successful in this field, as the Geneva manufacture uses a particularly resilient niobium-zirconium alloy as its base material. Automatic watches from Montblanc are also fitted with in-house springs. In Germany, the Saxon manufacture A. Lange & Söhne stands out above all. Technical expertise in hairsprings is so well developed in Glashütte that other members of the Richemont group benefit as well – Jaeger-LeCoultre, for example, is supplied with components from the storied small town.
One Step Ahead: The Mechanical Watches of the Future
The drive for constant improvement has been one of the forces behind watchmaking for centuries. It is hardly surprising, then, that the hairspring continues to evolve in the 21st century. One key innovation is the silicon hairspring: developed in a collaboration between Rolex, Patek Philippe and the Swatch Group, it features a layer of silicon oxide that further reduces the influence of temperature fluctuations on accuracy.
This is just one of many current achievements in the field of hairsprings: Precision Engineering AG, a supplier to the Swiss watch industry, presented a cylindrical, extremely precise version of the component as recently as 2018. It enables an even more uniform oscillation but involves a highly complex production process and will, for the time being, be found only in high-end models. Tag Heuer, meanwhile, recently unveiled its own graphene hairspring, which consists essentially of carbon and is said to offer exceptional robustness. Given such creative development work, we can look forward to seeing what innovations the future holds.
