A Visit to De Bethune Manufacture

A Visit to De Bethune, Perfecting Traditional Watchmaking

Part 1- The Manufacture

Don Corson

The manufacture De Bethune has its administration and R&D in this building in La Chaux, not far from the French border in the Swiss Jura.  De Bethune was founded in 2002 by two men with a long experience in the industry, Denis Zanetta and Denis Flageolet.

The view from La Chaux towards the Col d'Etroits, the pass which leads over to St.-Croix where Vianney Halter has his shop.

I was welcomed by Esthel Brunschwick, communications director and Denis Flageolet and first got a quick glimpse of the R&D operations, CAD and prototyping.  I noticed that Denis seems to have an entire machine shop for his own private use.

Assembly in the prototype lab.

There is always much to do in the R&D lab as the philosophy of the company is to create a new generation of timepieces incorporating the most recent technology and a modern esthetique.  As I learned during my visit the goal is not to throw out traditional watchmaking, but to critically investigate all the components and manufacturing techniques that are determining factors contributing to good timekeeping and use modern materials and technology when they improve the product.

De Bethune recently moved their production to this new facility in L'Auberson.  Just a couple km from La Chaux and the last village before the French border, L'Auberson was once known for the production of music boxes.  It is in one of these ex music box factories that De Bethune produces their watches.  The building has been completely renovated and will soon fulfill the requirements for Minergie, extremely low energy consumption buildings.  Already all the heat produced in the machining operations is recycled back into the building heating.

The building has three floors which lend themselves to separating their operations into part production, part finishing and watch assembly, with a floor for each.

Parts production using CNC machines is found on the ground floor.  According to Denis it was never the intention of De Bethune to produce all their parts, but in the meantime they do produce many of their parts.  They often require very particular  parts which their subcontractors are unable or unwilling to produce as they specified.  In such cases they have the choice of working with the subcontractor so they can produce according to the De Bethune specifications or learn how to produce those parts themselves.  Often they have developed new procedures, such as the bluing of titanium, and so do the work themselves.  But even where they use established subcontractors, such as for screws, they often require special materials.  All their screws use, for example, a special kind of stainless steel which is not otherwise used in the watchmaking industry.

Note here on the CNC milling machine that the part blanks are held down by springs and not directly by screws.  This allows knowing the holding force more exactly and avoids the warping that may come from an over tightened screw.  Denis has also banned the electro-erosion machines used for making small parts from his shop.  Electro-erosion has become a very common manufacturing technique, but Denis' research discovered that electro-erosion changes the surface characteristics of the steel used and for thin springs, for example, can mean that 50% of the parts do not work as desired.  Using today's super fine milling, with bits down to 0.1mm, it is possible to mill the parts that are otherwise made using electro-erosion.  Milling doesn't have the aggressive characteristics of electro-erosion that change the steels characteristics, but it takes much longer to do as only one piece can be made at a time.  The added time means, however, added quality.

Here we see a parts charger for the milling machine.  The machines work during the night without human supervision for operations that don't need the absolute highest levels of precision such as the first step in plate machining. 

Plates and bridges are machined in 3 steps at De Bethune.  Between the machining steps the pieces undergo a stress relief heat treatment.  The heat treatment facilitates the relief of stress in the pieces that would otherwise happen over the course of 10 or 15 years.  This can cause warping of the pieces with the ensuing loss of precision.  This three step machining eliminates possible future problems and the parts can be made to very high tolerances that they will hold. 

A small sampling of movement plates in different states of machining.

This shop also machines the small steel parts, levers, springs, hands, etc.

Note the multilevel stepped surface of an hour hand.

Very fine milling also has advantages for cutting gears.  On this micro-photograph two of them can be seen.  1) When cutting the gear profile the tool, spinning at high speed, follows the contour of the teeth.  This means that any machining marks follow the contour of the teeth, as can be seen here.  This makes for lower friction compared to the longitudinal machining marks from a standard module cutter that cuts in the perpendicular direction.  2) As the cutting follows tooth contour there is also less burr production.  This means that the gear plating can be done and in a final cleaning-up cut the plating can be removed from just the tooth contact surfaces.  This is important to provide low friction, high torque gearing.  Gold or rhodium are often used for gear decoration, but are not good materials for high torque gear surfaces.

In this room we see the galvanic installation, for plating nickel, gold and rhodium.

As the results of plating depend greatly on the cleanliness in the same room is the "laundry".  

For the washing and plating operations the individual parts are hung on conductive racks such as this one.

On the next floor we come to parts assembly and preparation.  Here all the parts are inspected individually.

An interesting operation carried out here is the making of the starry night skies.  Here we see the steel plates that will make the starry night sky back of a DBDigital.  Slightly offset from the middle is the large hole for the spherical moon.  In the picture you can just make out the holes drilled in the pattern of constellations on the plates.

In each of these holes a chisel punch is pressed twice to make 4 rays.  After smoothing the raised edges caused by the punch little gold studs are pressed in each hole.  Then the whole plate with the gold studs is smoothed and polished again leaving the star formed gold in the holes.  After flame bluing of the steel, which doesn't affect the gold at all, we are left with gold stars on a deep blue sky.  We will see the final product later.

Here flat springs are being deburred after machining.

This shows the first step in assembling a De Bethune balance.  This is the titanium frame finished after machining and after bluing.  This is one of the many instances of modern materials making their way into a De Bethune watch.  Ideally a balance will have all of its weight at the rim.  As this is hardly realizable using a very light material is the best alternative, with a very heavy material as the masselots.  Here the materials used are titanium and platinum.

The assembly starts with placing the balance staff, on the left, and continues with inserting the 18k gold adjustment weights, on the right.

The platinum masselots that will be placed on the arms of the balance are above the balances in the tray.

Each masselot is controlled to have the exact weight desire, 6.5 to 6.6 milligrams.

The finished De Bethune balance in all its glory.

Because the balance is not a closed ring modern automatic tools can not be used to do the equilibrium testing of the balances.  As can be seen here a standard old balancing tool with jeweled edges is used.

I hope you are enjoying this visit up 'til now.

In the second installment we will see more of the parts preparation and the watch assembly.

Don