Why did you and David establish De Bethune?
We wanted to create an all-new type of watchmaking. At the time, most brands were blocked from technical advancement because they had to use the escapements that were available from Nivarox. No one was really making their own movements. We wanted to be able to achieve our wildest dreams by uniting the aesthetic and technical visions of the brand. If David tells me he wants to do something, I will always say: “Let me try to find the way.”
Tell us about the in-house balance wheel that De Bethune introduced in 2004.
With a balance wheel, you want the greatest inertia combined with the lightest weight. This is good for chronometry as well as power reserve. I created a design with four arms in titanium, and then I removed the rim of the balance and placed a weight at the end of each arm, which can be adjusted to get the best result. When I tested it, it achieved a 20 per cent higher quality factor than a traditional balance. Since then, there have been modifications to the form to improve manufacturing precision and quality. For example, I flame-blued the titanium arms to stabilise them.
We are constantly evolving the design of the balance wheel. Take, for example, the one in the World Traveller. It is a titanium wheel with gold weights poised on it that act like the holes in a golf ball in that they start to generate their own momentum when in motion. The result is a beautiful balance wheel with greater aerodynamic penetration and better quality factor. We did experiment with silicon but we concluded that we preferred a metal hairspring with a very particular terminal curve.
What is the idea behind your terminal curve?
Firstly, we wanted to achieve what the Phillips terminal curve does but on a flat spring avoiding the need for extra height. Secondly, I don’t like the idea of bending the hairspring – if this is not done perfectly, the performance is compromised.
Instead by working on the outside of the curve, I can have the final part of the spiral slightly thicker, which is the same as having a greater active length to the spiral. By working with the profile and thickness of the outer curve, you can have a hairspring that breathes concentrically and retains its centre of gravity perfectly.
Also, because a traditional stud retains the hairspring between two pins, there is always some deformation at this point as the hairspring shakes between these two pins. When the watch is vertical, this shake causes the watch to lose amplitude and slow down. Our design allows the hairspring to be fixed rigidly using a single screw on one side only, which eliminates this problem.
The spiral is made of a normal (nickel-iron) metal like that you would get from Nivarox, however the material for the end curve is something we don’t tell anyone.