De Bethune is famous for their award-winning, space age watches. The architecture and aesthetics of the watches themselves are mesmerizing, but there is much more to De Bethune’s watchmaking than high-level finishing and interesting design. The brand has a deep focus on horological engineering, exemplified by the balances used in their watches. With each iteration, De Bethune strives for measurable improvements in performance. I spoke with De Bethune co-founder Denis Flageollet to learn more.
What was De Bethune’s motivation for moving beyond traditional balances in 2004 with the titanium/platinum balance?
One of the reasons for the creation of De Bethune was to bring to traditional watchmaking the result of new research. It was therefore logical to start the technical work on the improvement of the sprung balance which is the heart of mechanical watches. Since the 1970s, no one had sought radical solutions in this field. Partly due to the watch crisis of that time which had weakened mechanical watch research in favor of clock-making electronics. And for another part due to the fact that the balance is something difficult to achieve. Watch brands can be a little sleepy and prefer to buy standardized components, the same for decades. It was therefore time at the beginning of the third millennium that enthusiasts like us summed up this costly and difficult task of transcending the sprung balance into something more efficient, more mechanical, more modern and more emotional, certainly in the image of what the great watchmakers of the Enlightenment would have done.
How do you optimize the weight and inertia of your balances?
It is not the weight of the balance that is important, it is its mass in relation to its inertia. The aim is to have the lowest weight (mass) possible for the greatest inertia possible, the De Bethune balances are on average 20% lighter for the same inertia and the same radius of gyration as a standard balance. They are much more efficient in reducing disturbances they undergo on the wrist, but also for the energy gain necessary for their maintenance. It is known that in order to increase the inertia to the maximum in relation to a given weight, it is necessary to put the maximum of the weight outside. But be careful – it is not possible in the wristwatch to increase the diameter of the balance too much because it will be subjected to disturbances too important when the watch is on the wrist of the user. This is why the first De Bethune balances were made of titanium which is a light material inside the balance and platinum who is a heavy material outside the balance.
What was behind the switch to an annular balance in 2007?
The result of the annular balance with the integrated platinum inertia-block is a research on the aerodynamics of the balance. For a balance working on a 36,000 vibrations per hour it is important that its movement does not create air disturbances which may modify its operation. This research therefore began when De Bethune chose to increase the frequency of its balances to the maximum possible. This is for two reasons: an increase in the quality factor since this is proportional to the frequency of the oscillator, and further reducing the disturbance of the balance during the wear of the watch by its user.
Why did De Bethune begin using silicon in its balances?
Silicon is three times lighter than titanium, so it was logical for De Bethune to use silicon as the hub of the balance to achieve an even better inertia / mass ratio. To do this, it was necessary to develop very specific manufacturing and assembly techniques.
What is De Bethune’s testing methodology for the different iterations of its balances?
These are long and complex methodologies that can not be described here in detail, but in summary: it is important to carry out the tests with known points of comparison. We have therefore tested a long time in different conditions of the standard balances in order to have complete comparison tables to be sure of our results. It is important to calculate the quality factor for each type of balance tested, this is evaluated according to the damping standards of its oscillation independent of the escapement. It is also important to test the balance in all positions and conditions. The laser and the high-speed camera (more than 20’000 pictures by seconds) are excellent tools for carrying out all of these tests. The sprung balance and its escapement is a complex mechanical system, so it is necessary to modify only a tiny part at a time and to make the tests always under the same conditions to be sure of the action of a modification for the improvement of the overall.
How do you think balances will evolve in the future?
As long as the materials and assembling techniques evolve the balances will evolve. We are currently at the forefront of existing technologies and it is difficult to imagine what tomorrow’s balances will be. The improvements that we are constantly seeking to make according to the technologies available are: the reduction of friction at the pivot, the right choice of materials to further improve the effects of changes in temperature, better aerodynamics, and better inertia to mass ratio.
To learn more, visit De Bethune online.
Silicon / gold annular balance (2010)
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