Independents

A Visit to De Bethune, Perfecting Traditional Watchmaking

Part 2 – Finishing and Assembly

Don Corson

Continuing now on the second floor at the De Bethune factory in L'Auberson we come to the decoration shop.  Presentation pieces show some of the steps.  Here we see a DBS movement bridge after placing the côtes de Genève and polishing the bevels.  You can see the blackened remnants of polish sticking to the piece.

Here the bridge after being cleaned…

followed by nickel plating...

and rhodium plating.  Now the bridge is ready to have the jewels placed.  Note that these are just presentation pieces to show the steps of plating, all have defects that make them unusable for production, as you can see.

This is the machine to do colimassonage, snailing.  The work piece mounted is a platinum mass from a winding rotor.  The abrasive is on the bottom surface of the short cylinder on the right.  The work piece on the turntable is turned slowly with the abrasive head just touching the work piece to make a perfectly regular pattern.

Here we see the machine park for case polishing.  

One of the characteristic features of the De Bethune watches is the spherical moon phase indication.  Here we see the different stages of making the spherical moon.  We start at the top of the picture with 2 half spheres, one in platinum, one in steel.  The hemispheres are pressed together and given a final polish.  Then the entire piece is subjected to the bluing procedure.  The steel takes on its deep iridescent blue color while the platinum is completely unaffected.

The steel hands are flame blued, below we see the procedure.

The piece to be blued is placed on a bed of brass filings.  This is then heated over an alcohol flame.  The brass filings spread the heat but also allow reducing the heat flow to portions of the piece being blued.  If during bluing a portion, the tip of the hand, for example, is bluing too fast the filings at that point are pushed away so the piece doesn't touch at that point.  This practice reduces the heat flow at the point concerned and allows, with practice, to get good even bluing.

Here on the second floor is also the quality control of all the pieces, both purchased and made in house.  This is optical dimension control.

In general, at De Bethune work is done in batches of 10 pieces, as it was common in the industry in earlier times.  A feulle-de-route accompanies the pieces through their entire parcours through the shop, including QC procedures at each step.  These are platinum rotor masses.

Case parts, here polished titanium.

A heat blued titanium bezel.  To my question about the robustness of bluing on a part that is as exposed to scratching such as the bezel Denis replied that titanium bluing is more robust than steel, but of course it does scratch.  The big advantage in comparison to PVD, which scratches too, is that there is no special equipment needed to re-blue.  Bluing titanium is not difficult and any good watchmaker can disassemble the bezel completely and then re-blue the piece if needed.

We have mounted another flight of stairs to the domain of the watchmakers.

Different from many companies these days, De Bethune divides the watchmaking work into different steps with watchmakers specializing.  Although they can't say that one watchmaker did the entire assembly this way of doing things has the advantage of better quality control.  The first step a watchmaker does when he/she receives a watch is to make sure that the previous work was done well.  At this bench the watchmaker is adding the complication to allow adjusting the rotor "speed".  Here we can see the 10 movements in a case with the parts that will be added in the trays on the right.

Here we can see the under rotor mechanism for the « speed control ».

Seen on another work bench, a perpetual calendar.

The little night sky surrounding the moon sphere on the perpetual calendar.

Assembling the basic movement.

Looking out the window of the watchmakers shop.

A DB2015 movement on the bench.

The rack with the hand for the power reserve indication.

The rack with hand installed.  Note the fine finishing under the dial.

At this workbench the hairsprings are mounted on the balance and counted.

The balance and hairspring are subject to Denis Flageolets special attention.  They form, of course, the oscillating system that determines the watches timekeeping qualities.  Not content to simply purchase these parts from Nivarox which means being no better than anyone else in the domain De Bethune has made several advances in this domain. 

The first is in the terminal curve of the hairspring.  Denis has developed a terminal curve which allows the hairspring to develop concentrically in all positions.  This fulfills the same objectives as the Breguet overcoil while allowing the hairspring to remain flat, saving space, manufacturing time to bend the overcoil and stress in the hairspring itself  from the overcoil bending process.  This terminal curve is made of a special material which is "top secret" and is clipped on the end of a flat hairspring.

De Bethune also uses their own balances where they try to get close to an ideal balance by placing as much of the weight as possible on the exterior rim and to eliminate the mass of the supporting structure connecting to the balance shaft.  They do this presently by using a light weight titanium structure with platinum weights.  De Bethune has been improving their balance almost yearly and in the future will be converting to a balance structure using a silicon disk with a platinum ring at its outer edge as has already been make for their "Dream Watch 1".  Keep an eye out for these new developments.

Ready to house the movement and mount the hands.

Denis discussing with a master watchmaker suggesting an improvement on this QP movement.

I hope you are continuing to enjoy this visit.

In part 3 we will take a look at some finished watches.

Don

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