Dr. Ito's thorough analysis of mechanical watches!! Vol.4 ~ What is the difference between a mainspring and a hairspring? ~

Good evening, everyone!

This column discusses mechanical watches from an engineer's perspective. For the fourth installment,

"Mainspring and Hairspring, what's the difference?"

We will be discussing this topic. It seems that many customers, whether in-store or over the phone, sometimes confuse the "mainspring" and "hairspring."

These two, despite their similar names, are completely different. Both play crucial roles in mechanical watches, so I hope this opportunity helps you understand their differences.

About the Mainspring

What is a Mainspring?

*Mainspring

The mainspring is what powers a mechanical watch. It is sometimes called the "mainspring" to distinguish it from the "hairspring."

It has a somewhat peculiar "treble clef" shape, which is designed to minimize the difference in torque (rotational force) between when the mainspring is fully wound and when it unwinds.

*Mainspring housed in the barrel and the barrel arbor

The mainspring is housed inside a gear called the barrel. When the crown is wound manually or when the watch is wound by arm movements (for automatic watches), the kinetic energy is transmitted through the automatic winding mechanism, the ratchet wheel, and the barrel arbor, causing the mainspring to wind up.

*Mainspring, barrel, and barrel arbor

If the mainspring is completely removed from the barrel, it measures about 10-odd centimeters in its treble clef shape, but when straightened, its total length extends to over one meter.

The power of the wound mainspring passes through mechanisms unique to mechanical watches, such as the "train, escapement, and regulating system," slowly unwinding and continuously moving the watch hands precisely.

As you may have gathered by now, the "mainspring" plays the same role as the "spring that powers mechanical toys" that you imagine. It is the component that provides the power, wound by hand, and by unwinding, it moves the object.

The Importance of the Mainspring

*Mainspring (left) and the balance assembly including the hairspring (second from bottom center)

The power reserve (driving time) of a mechanical watch is mainly determined by the length of its mainspring; the longer the mainspring, the longer the watch's driving time. Therefore, each manufacturer devises ways to incorporate longer mainsprings, such as making the inner wall of the barrel as thin as possible, to extend the power reserve.

Also, "twin barrel" movements, which incorporate two barrels, were actively developed for a period. The purpose of this was to increase the driving time by increasing the storage space for the "mainspring," which is the power source, and some models achieved astonishing power reserves of approximately 8 days.

About the Hairspring

What is a Hairspring?

*Hairspring

The hairspring is a component that forms part of the balance, the heart of a mechanical watch, and plays a crucial role in determining its accuracy.

As its name suggests, it is made of a thin metal as fine as hair (it's interesting that it's called "hair" in English, but "beard" in Japanese), beautifully shaped into a spiral. It's a bit hard to tell from the photo, but it's a much smaller component compared to the mainspring, usually less than one centimeter in diameter.

*Hairspring attached to the balance wheel

The photo above shows a complete balance assembly, also known as the "regulating organ" in watch terminology.

If we compare the balance wheel to a pendulum, the hairspring acts as the "pendulum's string." As the hairspring repeatedly expands and contracts, the watch keeps accurate time. However, a wristwatch is not always kept in a constant position like a desk clock; it can be sideways or upside down, subjecting it to changes in gravity. Furthermore, there are constraints requiring various components to fit into a very limited space, which ultimately led to the development of hairsprings with such delicate shapes.

Moreover, although the hairspring may appear to be just a metal thread, its manufacturing is considered one of the most challenging aspects of watchmaking. This is because the hairspring is the most critical component for determining accuracy, requiring it to be manufactured with greater precision than any other part. From the molding process to the heat treatment and length adjustment, there is no room for compromise in its production.

Types of Hairsprings

*Omega's in-house Si14 silicon hairspring

Previously, most Swiss mechanical movements used components from "Nivarox-FAR," a specialized hairspring manufacturer. However, over the past decade or so, there has been a rapid increase in hairsprings developed and produced in-house by various brands.

I would like to briefly introduce two of the most prominent types among them.

1. Blue Parachrom Hairspring

The "Blue Parachrom hairspring" developed by 【Rolex】 in 2005.

The Blue Parachrom hairspring is a distinct blue-tinged hairspring called "Parachrom," composed of an alloy of Nb (niobium) and Hf (hafnium), and is characterized by its exceptionally beautiful appearance.

It is also extremely resistant to temperature changes and shocks, and boasts superior antimagnetic properties compared to Nivarox hairsprings.

2. Silicon Hairspring

*【Rolex】Syloxi hairspring

Currently, the "silicon hairspring" uses silicon, which is highly valued by various watch brands in their hairspring development efforts.

Silicon possesses the most essential characteristics for a hairspring: it is "unaffected by magnetic fields, lighter than metal, and resistant to deformation," and it also has strong resistance to corrosion and shock. While this sounds like a panacea for watches, from an engineer's perspective, there is also the point that "fine adjustment during assembly is unnecessary (and impossible due to the material's properties)."

Nivarox hairsprings and Blue Parachrom hairsprings, mentioned earlier, required precise adjustments by engineers during installation, which was a very delicate process that affected the watch's accuracy—a true showcase of an engineer's skill. The fact that this adjustment is no longer necessary, while being a welcome "evolution," is also a little disheartening for engineers when assembly can be done without specialized skills.

Rolex currently uses two types of hairsprings, Blue Parachrom and Syloxi, interchangeably depending on the movement. Based on their respective suitabilities, I believe they will continue to coexist in the future.

Summary

Mainsprings and hairsprings—their similar names can be confusing, but I hope you now understand the difference. Both play vital roles in wristwatches, so by understanding their distinctions and imagining how a mechanical watch works, I believe you'll grow to love mechanical watches even more.

I hope this article has provided useful information and sparked your interest in luxury watches! If you have any questions, please feel free to ask directly. We look forward to your visit and inquiries.

Stay tuned for the next installment! See you then!