A mechanical-watch hairspring is not simply wound from wire and installed. Conventional production combines a temperature-stable alloy, repeated annealing and deformation, precision coiling, a form-setting heat treatment, and extensive hand finishing at the collet, overcoil, stud and balance. Silicon hairsprings follow a different family of production: deep-ion etching of a shaped spring from a silicon wafer.
The manufacturing sequence at a glance
The exact machines, tolerances and alloy recipes used by individual factories are generally proprietary. Public technical descriptions nevertheless establish a consistent sequence for metal hairsprings:
| Stage | Purpose | What public sources establish |
|---|---|---|
| Material preparation | Provide a suitable, temperature-stable and, in some designs, amagnetic alloy stock | Nivarox-FAR documents balance-spring alloy development; patents disclose niobium-hafnium and niobium-zirconium routes. Nivarox-FAR, EP3736639B1, EP3736638A1 |
| Annealing and deformation | Make the stock workable, then reduce it to fine wire or strip | The Nb-Zr patent describes annealing followed by rolling or drawing; a ductile surface layer can make forming easier. |
| Coiling | Give the wire its flat spiral and terminal geometry | The wire is wound or otherwise shaped; the cited production text describes a later heat treatment to retain that form. Technology of Watch Production |
| Form-setting heat treatment | Stabilize the spiral and tune thermoelastic behavior | Patent-specific temperature and time windows are disclosed, but they are not universal recipes. |
| Attachment and finishing | Secure the inner end, shape the overcoil, level and center the spring | Watchmaking instructions describe pinning, trimming, bending, leveling and centering by hand. AWCI, Horological Times |
| Regulation | Match the spring and balance as a running oscillator | The finished assembly is vibrated or timed, then secured at the stud and adjusted. |
How a conventional metal hairspring is made
1. Select and prepare the alloy
The starting material must keep its elastic behavior stable as temperature changes and must tolerate extreme cold working and heat treatment. Nivarox-FAR describes its work on balance-spring alloys and identifies Nivachron as an amagnetic alloy development, but the company does not publish one single composition for every product sold under the Nivarox name. Public patents show that more than one alloy family is possible, including niobium-hafnium (Nb-Hf) and niobium-zirconium (Nb-Zr) systems.
One disclosed patent route begins with an alloy blank and an anneal, followed by controlled cooling. Another describes adding a ductile layer—copper, nickel, cupro-nickel, cupro-manganese, gold, silver, nickel-phosphorus or nickel-boron—to assist subsequent forming. The coating is a processing aid, not evidence that every finished hairspring has that layer or that all Nivarox products share one recipe.
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2. Anneal, roll and draw the stock into fine wire
After annealing reduces hardness and relieves unfavorable internal stresses, the blank is progressively deformed into wire or strip. Rolling and drawing reduce the cross-section while controlling the material’s texture and surface condition. The Nb-Zr disclosure specifically discusses a ductile surface layer to facilitate these operations.
Factory wire diameters, the number of reductions, intermediate anneals and machine settings are not stated in the cited public sources. Those omissions matter: a production line’s reduction schedule affects surface quality, residual stress and the consistency of the finished spring.
3. Coil the wire into the spring geometry
The prepared wire is wound or otherwise formed into the required spiral. The geometry is not limited to the circular coils visible from above. The spring must also have the correct spacing, flatness, inner attachment and outer terminal shape, whether a simple terminal curve or a Breguet-style overcoil.
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Coiling alone is provisional. A technical watch-production text explains that a form-fixing heat treatment is used so the metal retains the spiral imparted during coiling. This is why a spring that looks correctly wound can still be unfinished and mechanically unstable.
4. Heat-treat the form and thermoelastic response
Heat treatment performs two linked jobs: it fixes the imparted shape and adjusts the spring’s thermoelastic behavior, helping the balance remain more stable across temperature changes. The publicly documented windows belong to particular patent processes:
| Patent route | Disclosed final treatment | How to interpret it |
|---|---|---|
| Nb-Hf, EP3736639B1 (published 2024) | 500–1250 °C for 30 minutes–30 hours | A broad range claimed for that process, not a recipe for every alloy or manufacturer. |
| Nb-Zr, EP3736638A1 (published 2020) | Preferred 650–750 °C for 30 minutes–2 hours | A preferred window in that disclosure, not a universal hairspring specification. |
Temperature, duration, atmosphere, prior deformation and alloy composition all interact. Applying one number from a patent to an unrelated spring would therefore be unsafe.
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5. Secure and trim the inner end
The inner end is attached to a collet—the small carrier that mounts the spring to the balance staff. In the AWCI procedure, a taper pin is pulled with 90-degree cutting tweezers; excess ends are cut away and rough projections are shaved so they cannot contact the inner coil. This is delicate work because a tiny protrusion or an incorrectly seated pin can disturb the spring’s freedom of motion.
The use of specialized tweezers is not cosmetic. Their shape gives the watchmaker access around the pin while minimizing the risk of bending adjacent coils; the AWCI instructions specifically refer to 90-degree cutting tweezers for this operation.
6. Form the terminal curve or overcoil
The outer end determines how the spring breathes concentrically as it expands and contracts. For a Breguet-style overcoil, the watchmaker removes the spring from the balance and makes a rise bend, a leveling bend and the terminal curve. Each bend changes the spring’s spatial relationship to the balance and to its neighboring coils.
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Not every movement uses the same terminal design. A flat terminal, a raised curve and a full overcoil are different geometries, so the finishing operation must match the balance, stud and regulator arrangement for which the spring was made.
7. Level, center and attach it to the stud
Once the inner and outer ends are shaped, the spring is checked on a spinning balance. Slight manipulation near the collet is used to level and center it; the coils should move smoothly without visible wobble. The outer end is then secured at the stud, the balance-and-spring assembly is vibrated or otherwise timed, and the final adjustment is made.
This explains why hairspring manufacture is both an industrial and a watchmaking process. Alloy preparation and wire production can be highly specialized factory operations, while the last geometric corrections are sensitive manual operations performed on the individual balance.
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How silicon hairsprings are manufactured
Silicon is not made into a hairspring by drawing a metal-like wire and winding it. Blancpain describes the distinction directly: “This type of balance-spring, made from a Nivarox alloy, requires more than 15 traditional operations, from treating the wire to determining its definitive shape. The second family, the silicon balance-spring, is the result of a completely different manufacturing process: deep ion etching on silicon disks, called wafers.”
In that route, the spring’s plan-view shape is defined lithographically on a wafer and transferred by deep reactive ion etching. The result is a precisely patterned, flat component produced in wafer batches rather than a length of alloy wire that must be coiled. The wafer process changes how geometry is created; it does not eliminate the need for a compatible collet, terminal arrangement, balance assembly and timing adjustment.
Metal and silicon routes compared
| Comparison point | Metal-alloy hairspring | Silicon hairspring |
|---|---|---|
| Starting material | Temperature-stable alloy stock; public Nivarox-FAR patents include Nb-Hf and Nb-Zr alternatives. | Silicon wafer. |
| Shape creation | Anneal, roll or draw to wire, coil, then set the form with heat. | Deep-ion etch the spring geometry into the wafer. |
| Finishing operations | More than 15 traditional operations are cited by Blancpain, including wire treatment and final shaping. | Different wafer-based sequence; the cited sources do not provide a universal operation count. |
| Terminal geometry | Formed through manual or dedicated bending operations, including flat terminals or overcoils. | Defined in the etched pattern, with assembly-specific attachment features. |
| Temperature and magnetic behavior | Depends on the chosen alloy and its heat treatment; Nivachron is described by Nivarox-FAR as an amagnetic alloy development. | Uses silicon’s material and etched geometry; exact performance depends on the specific design and balance system. |
| Service implications | Traditional watchmaking techniques can manipulate and replace the spring, but the work is highly skill-dependent. | The cited sources do not establish a universal serviceability ranking versus alloy springs. |
What “Nivarox” means—and what it does not mean
“Nivarox” is often used as if it identified one chemical formula. The public evidence supports a narrower conclusion: Nivarox-FAR is a manufacturer and developer of balance-spring materials, and its patents cover different alloy routes. A watch described as having a Nivarox spring therefore does not, by that label alone, reveal the exact alloy, coating, heat-treatment schedule or terminal geometry.
The same caution applies to the question “What is Nivarox made from?” The answer depends on the product and process. Nb-Hf and Nb-Zr are documented patent examples; Nivachron is identified as an amagnetic alloy development; proprietary production compositions and complete quality-control specifications are not published in the cited material.
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Why the final hand operations matter
- Concentric breathing: uneven centering makes the coils move off-axis as the spring expands and contracts.
- Flatness: a level spring is less likely to approach or touch adjacent components during its motion.
- Clearance: trimming and shaving at the collet prevents projections from contacting the inner coil.
- Terminal control: the rise, leveling bend and overcoil position govern how the outer coils participate in the oscillation.
- Timing: the spring is not finished when it has the right silhouette; it must be matched and regulated with its balance.
What remains undisclosed in public descriptions
Published patents and watchmaking texts explain the operations and give examples of process windows, but they do not provide a complete factory specification. The cited material does not establish particular machine models, production throughput, universal wire diameters, reduction schedules, all quality-control tolerances or every proprietary alloy recipe. Those details vary by manufacturer, spring design and production generation.
The practical answer
A conventional hairspring is manufactured by turning carefully prepared alloy stock into fine wire, repeatedly controlling its mechanical condition, forming and heat-setting a spiral, then completing the collet, terminal curve, leveling, centering and regulation by precision watchmaking. Silicon springs bypass wire coiling entirely: their geometry is etched into wafers. Neither route is adequately described by “just winding a spring”; the alloy or silicon process and the final three-dimensional geometry are equally essential to the oscillator’s performance.
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