The X-Files
The Quest for a Mechanical Rapprochement of Quartz-Accuracy

An inside report of De Bethune SA, La Chaux l'Auberson

by Magnus Bosse, November 2006

Part 3
click on small images to view full-size ones!

3. De Bethune's bespoke movements and the unique "spider" balance assembly
3.1 The characteristical De Bethune movements: The lyrical heart of a watch!
Imagine you are a contemporary movement designer and your task is to construct an entirely new line of movements, rooted in watchmaking tradition, but with a distinctive technological departure, and intended to mark a new departure for the manufacture. That was the challenge for Mr. Flageollet, and he and his team delivered an admirable feat.
What strikes me is the consequence, far-sightness and dedication that De Bethune followed during the path of the creation of this new line of movements. The signature calyx-shaped main plate, the red gold wheels (see part 2!), the extended power reserve (achieved by two mainspring barrels, which also provide for consistent power delivery into the gear train), its flat construction and its flexibility towards unique and elegantly designed complications are all but a sign for the love of art of finest watchmaking. The result is a manifestation of a holistic approach towards Haute Horlogerie and reconciles technical, aesthetical and finishing aspects. Of importance in this context is the fact that De Bethune is a very small manufacture, but yet decided to opt for the troublesome path of proprietary developments.


As already mentioned (and visible in the large picture above), there are several original aspects in this movement. Beneath the obvious shape of the movement plate (small images, left), there is for a start the scorpion-like anti-shock device, named by De Bethune as "triple para-chute" (obviously referring to A.L. Breguet's Parachute shock absorbing system), three-fold shock protection (small images, middle left and middle right). Such a device consists of - starting from the balance wheel - a widely used Incabloc shock absorber (1st shock protection), mounted on a flexible titanium bridge (2nd shock protection), which is itself supported on a the main clockwork plate via two rubies, and a spring shaped like scorpion's clams (3rd shock protection). De Bethune claims that any sudden movement the watch is subjected to is damped three times before it reaches the watch's most sensitive organ, the balance wheel.
This may be a very sensible solution to combat the detrimental effects of unforseen heavy shocks, but it of course raises concerns about the skills and experience necessary to assemble such a system (think about service!). The De Bethune triple para-chute looks fantastic, but does it really over a value added?

So what were they thinking when developing such a system? Confronted with such concerns, De Bethune assured me that "... our triple para-chutes consists of a standard shock absorber in the center for the balance-wheel, this one is adjusted in the same way that all the shock absorbers in quality movements, and of two shock absorbers for the balance-wheel bridge which are calculated and regulated like springs in the precise watch industry. More precisely, if the titanium bridge of the triple para-chute undergoes a shock of 5000G (equal to a fall from 1 meter on wood), it becomes deformed to approximately 0.003 mm only! If it subjected to a force of approximately of 20 Newton, which corresponds to approximately 2kg, the use of a titanium bridge by De Bethune reduces the force hitting the balance to less 10 Newton." Judging from these rather impressive data (I have however no comparison to standard shock protection devices used in high-grade watch movements), it seems to me that indeed the triple para-chute is quite well conceived for every day usage, as it dampens any shocks significantly, while still maintaining the precise positioning of the balance needed for a contemporary high grade watch. To say the least, it occurs to me that such concerns have duly been taken into consideration while designing the movement. However, it seems that only the balance pivot on the dial side features the triple para-chute system. Thus, the question arises how the above mentioned figures are derived, as only one of the balance pivots is protected with the elaborate solution.

3.2 Spiders Webs and Legs... The De Bethune Isochronic Oscillation System (IOS)
Immediately when looking at the pics under 3.1, you will notice the uniquely shaped balance system. The balance does not follow known paths with a round balance wheel, instead it is X-shaped like spider's legs, and eye-catching platinum, ogival formed weights (think of the lugs we were discussing at the beginning of this article!):


The system currently employed by De Bethune is termed Isochronic Oscillation System (IOS). The name already hints the ends to which these solutions are created: Optimal isochronism throughout an extended period of autonomy (power reserve) of the watch movement. What initially looks very futuristic is in fact a significant modification of the well-known balance designs in terms of innovative balance and hairspring concepts:
De Bethune chose to replace the rather conventional circular balance with cross or more recently an X-shaped (or spider-like) scaffold made of heat-stabilised (and thus also blued!) titanium, in which the balance axis is mounted in its center joint. This design provides for a very light construction (density of titanum: 4.49g/cm3) with high elasticity. The necessary moment of inertia as well as the regulation is achieved with nearly concentrically situated platinum weights (density 21.45g/cm3) on the outer sites of the balance (small images left and middle). These weights can be moved on their supporting arbors to regulate the rate of the watch (implying that the arbors are not parallel to the imaginative circle of the balance). Interestingly the platinum weights are aerodynamically shaped to reduce disturbances caused by turbulences. With this design, De Bethune realised "the lightest balance with the relatively highest inertia ", as claimed in their patent application. Put in other words, the benefit of this construction is that almost the entire weight of the balance system is located on its outer ends, resulting in a large relative inertia-mass ratio of the balance, which helps to safeguard great isochronism (isochronism describes the uniformity of a balance's oscillation, that means the stability of an escapements' frequency unaffected from external perturbations). Such a solution was hitherto mainly employed in precision marine chronometers.
A second distinctive feature of the De Bethune IOS is a two-element balance spring (with a more traditional inner part (though not from Nivarox, but from a dedicated French collaborator) attached to a unique looking, proprietary outer curve; small image right)), termed isochronal balance spring. The outer curve is manufactured from a material of a non-disclosed alloy, and features three characteristical bends. The connection between the concentrical inner part and the outer curve of the balance spring is achieved by a special UV collage glueing technology.
The benefit of the De Bethune isochronal balance spring is, according to Denis Flageollet, that this system allows for an equally free "breathing" of the hairspring like an overcoil hairspring, but without its conceptual quirks (these are best described with the problematic force necessary to bend the terminal end of the spring upwards. This perpendicular to the balance area and not parallel, resulting in internal disturbances of the sensitive spring). As an additional benefit, the balance spring is significantly flatter than a overcoil hairspring.

The current state-of-the-art IOS 4 represents the culmination of several years of experience with this unique balance design (please note that the actual shape of mentioned components vary from the very calibre they are implemented. Here, the basic differences in terms of technical or materiological changes are important, not the actual realisation in different movements):

  • IOS 1 (which introduced the titanium spoke balance (originally 3, later 4 spokes), the platinum weights and the De Bethune balance spring; small images above, left)
  • IOS 2 (which introduced the triple para-chute shock protection and the titanium balance bridge; small images middle left);
  • IOS 3 (which presented the X-shaped balance and the regulation system; small images middle right);
  • IOS 4 (which is the first implementation of Silicium in a De Bethune balance; small images right).

The latter two are the most advanced and interesting ones, and will be described more detailled below:


The two designs, here shown are IOS 3 (top drawing) and IOS 4 (bottom drawing), demonstrate the underlying concept. The difference lies more in the metal than in the shape: IOS 3 combines the De Bethune balance spring assembly with a titanium base, with an adjustment device bridging two legs each. The temperature correction is entirely implemented in the balance system. The use of titanium for the base already results in a significant reduction of weight compared to Glycidur by about 20%.
The IOS 4 finally pushes this technology to just another level: it features both a Silicium x-shaped balance as well as an inner balance spring made from pure mono-crystalline silicium (110 type wafer which is said to have superior mechanical properties), combined with De Bethunes landmark terminal curve. The manufacturing of the Silicium parts is achieved by “proton beam writing”, a proceeding executed in the total vacuum at – 273° Celsius inside a cyclotron.
The last word is a hint: cyclotrons are not very wide spread, and I guess somewhere around Geneva (where the CERN is located) an university spin-off delivers frequently to La Chaux... With these modern materials, De Bethune increased the inertia-mass ratio further: the center X-shaped part weights only a mere 0.043gr (yes, the "0" after the "." is correct!)!!! BTW, Silicium is flexible enough to allow for a temperature compensation by U-shaped bi-metal elements between the balance legs.

What might interest many of you, is that the IOS systems are interchangeable, and thus a given movement can optionally be upgraded to the newest balance version, given the technical and qualitative improvements grant such a modification.
The first IOS was devised in 2002 and subsequently has undergone thorough testing before it was released to the market in 2004. Over the years, De Bethune has gained significant experience with the production of UV welded two-component balance spring, which was the main reason why this design was kept when the decision to opt for Silicium as balance component was made.

3.3 The De Bethune Moon - a sphere, not a disc, of course!

De Bethune knows well about mankind's fascination with astronomy, particularly with our constant planetary companion, the moon. The moon's cycle of approximately 29.5 days, during which he rises, glows in his entire beauty and then slowly disappears, determines decisive circumstances in our daily life, such as tides and most importantly, the secular calender. No wonder the Moonphase complication ever attracted many watch aficionados.

As many of you already know, De Bethune surprised the public with its mesmerising spherical Moonphase display at the Basel Fair 2003. De Bethune presented its unique design of a moon ball consisting of blued steel and platinum, each one half sphere, rotating on an axis parallel to the plane of the dial. The effect is quite dramatic, just as lookking at the real moon:

De Bethune has devised a solution that, beneath being highly accurate (for up to 122 years!), also gives the moon a 3-dimensional shape: The moon is realised not as a common disk, but instead as a sphere which rests upon the dial. The large picture shows a Perpetual Calender plate (dial side) with the prominent moon sphere at 11 o'clock. The moon is driven by the movement via a planetary gear system (small images, left), which is conceiled by the finely finished top plate of the Perpetual Calender module (small images, right).
The mechanism shows a remarkable resemblance to Paul Gerber's 3-dimensional Moonphase display, but this is a mere coincidence. They were both presented in 2003, but differ technically (Paul Gerber's solution is integrated into the movement and driven differentially, to name the most prominent distinctions).
Even much earlier, the manufacturer Bunz offered a three dimensional moon phase indication.


The process of creating the moonphase ball is a fascinating example of traditional watchmaking techniques at De Bethune. The half-spheres made from steel and platinum are melted together, polished (small images below, left) and are then subjected to a very demanding and precise blueing process by heat. The process is, depending on the thickness of the materials, very short and requires great skill, fast reaction and tremendous experience. Heat-blueing always results in differences in the blue colour. Therefore, many manufactures do batch-processing in order to achieve more consistent tones. Even then, individual selection of, for example, hands are necesssary to avoid tonal inconsistencies. Note that the moon ball cannot be blued together with hands (as the difference in material dimensions would be too big).

The steel part of the sphere changes its colour gradually from the typical steel colour (image sequence above, starting with the initial steel colour (a) over brown (b) and red to blue (c). Finally, the sphere is ready and can be mounted in a De Bethune watch (image below).

Now, after we tackled the characteristics of De Bethune's art of watchmaking and their impressive basic philosophy of timepieces, we are well prepared for a journey through De Bethune's collection of landmark watches. Please follow me through the next chapter!

Part 1 - The Introduction
Part 2 - Watchmaking at De Bethune today
Part 3 - De Bethune's bespoke movements and its unique "spider" balance assembly
Part 4 - The current De Bethune collection - Part I
Part 5 - The current De Bethune collection - Part II