This is the fifth in a series of six articles, by Maximin Chapuis, a French watchmaker, which takes a look at traditional finishing skills that are all carried out by hand.
In the last TP, we saw different bevelling processes, so now I want to look at the most noble technique – handmade bevelling. Today approaches to this type of bevelling vary greatly depending on each individual workshop and of course, the final cost of production of the time piece. Here, I will try to present to you the most complete processes, highlighting which tools are required and offer recommendations on how to sharpen and care for them. I hope that each person who would like to start trying bevelling will be able to find their own functional process with their own personalised tools. Of course, an infinity of tools and processes remain to be discovered.
1. Preparing tailor-made bevelling files First of all, angles are formed thanks to a set of files, that have been previously sharpened. Needle files with different shapes are required to ensure that we can bevel each edge around a complex design of bridge or component with external, inner or rounded angles. The most useful are the square file, the 3-square or triangle file, the oval crossing file and the small crossing file with two smooth surfaces on its top. Then, the top of each file has to be cut out to reduce the length of the working surface with teeth. With the index finger at the back of this working surface, the craftsman can feel everything under his finger and be much more precise.
The side of each file needs to be ground to have very sharp edges. This is essential to make inner angles. You can grind the file with stones and polish the edges to make them harder. Files are very personal and they cannot suit anyone else but the owner. It takes a significant time to make these tools and the quality of the work must be irreproachable.
I really recommend having a set of common and useful needle-files sharpened and functional for all adjustments when making components, and one set of bevelling files exclusively reserved for each material to bevel, ie one set for brass, one for steel and a last one for titanium which is becoming more and more common in modern mechanical constructions.
All these files must be maintained with the utmost care according to the requirements of the profession, they must never touch each other and must be preserved from corrosion. When the material is too hard, like a titanium bridge, we can also use the little known cabron files. The word cabron (French) translates to ‘carbon buff sticks’ or ‘Emery buff’ in English, which are extremely smooth diamond files. They are very useful, Figure 1, especially for tiny components cut by wire cutting electrical discharge machining (or wire EDM, or spark erosion) leaving a hard, tempered surface. These files can also be used to replace degusit stones.
2. Rising edges, the first steps It is important not to create any twisting and all the bevels around a component must be the same size when we inspect the component from the top and each side. Filing is done with a constant pressure and a straight movement with criss cross motions to clearly see where the file is working. We can start forming bevels with Vallorbe files N°6 if the bevel is of significant size and then use smaller ones, or start directly with files N°8.
Perpendicular marks left by the file’s teeth are eliminated by using a smooth file with straight movements in the direction of the bevel, working from side to side without moving it forward (‘draw-filling’), starting from inner angles so as not to damage them. Then, taking care to keep a flat bevel (on a classic 45° chamfering), smoothed using degusit stones, Figure 2, and then using cabron buff sticks covered with fine diamond abrasive paper, Figure 3. Increasingly, we use smoother and smoother ones until the bevel starts shining. Each cabron buff stick is held between the thumb and the index finger at the top of the tool like bevelling files.
As my teachers in Paris said, it’s like using a file ‘it is important to criss-cross the motions so as to clearly see the work of the buff stick’. Using that technique, you are sure of the homogeneity of the bevel, and the quality during all the steps remains irreproachable.
Some bevellers don’t like to use cabron with abrasive paper and use pegwood with fine abrasive (see boxwood and pegwood
on Figure 3). Each has to be smoother than the previous, eg, using 12 microns paper then a 9 micron one, etc. We change the abrasiveness when the surface of the bevel is perfectly homogeneous.
Before adding a new abrasive on the top of the pegwood, this one must be cut and shaped again to eliminate all the previously used paste with bigger grains. If only one grain remains and is mixed into a finer paste, the task will become impossible to achieve. Between each paste, all bevels must be cleaned with elder pith and isopropyl alcohol, once again to eliminate all the previous paste. Shoemaker sharp blades are the best tools to cut bevelling woods.
After all this work has been done with care, we must then burnish the surface of the bevel to allow us to be able to polish it afterwards. For this step, we use a burnisher (see Figure 3), a tool in tempered steel and polished with diamond paste to remove marks. We can make a high quality burnisher by entirely grinding the teeth off an oval-crossing needle file by hand, using stones to avoid drawing the temper, keeping it very hard, and then polishing it. We then apply very fine diamond paste on the newly made chamfer, generally 1 or 2 microns to start and finer grades to finish burnishing it. This step of cold-working the material makes it much harder on its surface in addition to making the polishing easier.
Sometimes, unexpected tools can be involved in the smoothing or polishing procedure. Using a Plexiglas rod sharpened like a screwdriver, Figure 4, with diamond paste allows the grains to grab the Plexiglas and because it is stronger than some woods, the 45° chamfer’s flatness is easily conserved. Testing with an old piece of ivory or cow horn has a very similar feeling. This material was used a century ago to do circular graining (or perlage in French) on traditional Swiss mainplates. Its hardness keeps the mainplate flat instead of removing too much material with new synthetic abrasive sticks. The most important thing is to find a way that suits you personally to make the rough bevel smoother and smoother until final polishing.
4. Suggested procedures
Tools in order for the first procedure could be the following:
– File N°6 or 8 depending the strength and the size or the component
– Straight graining with file N°8 or 10
– Surface is smoothed with a degusit stone according to the shape of the component, Figure 5 and 6.
– Boxwood and fine abrasives (buffs)
– Burnishers and fine diamond paste (burnishing)
– Pegwood (smoother than boxwood) and extra fine diamond paste (0.5-1µm)
Second suggested of procedure:
– File N°6 or 8
– Cabron file (extra smooth diamond files)
– Cabron buff 9µm (start with 12µm if needed)
– Plexiglas rod with 6µm diamond paste
– Plexiglas rod with 3µm diamond paste
– Pegwood and extra fine diamond paste (0.5-1µm)
5. A secret technique from the Jura Mountains Finally, the ultimate radiance is achieved by rubbing bevels with very fine diamond paste using a piece of wood (pegwood, boxwood or even ebony wood, for example for titanium components, depending on the strength of the material to be polished).
Another deep shine step was applied to bevelling in the Vallée de Joux. A long time ago gentian wood stems, which had been dried for a few years, were used. Thanks to the marrow inside the stems, the extra fine polishing paste can be applied with a very gentle support. A tube of gentian stem is cut into two or three parts along its length, see Figures 3 and 7.
The last steps of the hand-finishing process can easily damage the previous handmade work so be careful! Only the gentian’s pith must touch the newlypolished chamfer, the gentian stem bark must not come into contact with it or all the work will be damaged. This plant is protected, we must respect it and can only cut stems which have naturally dried in the fields – the rest of the plant mustn’t be touched. The old folks used to say ‘the higher the gentian stems the more snow will fall the coming winter’. And that, of course, would give longer days of work and hand finishing for watchmakers…