High-end
bevelling : methodology
Bevelling
is undoubtedly the most significant determining factor in aesthetic
terms : this extremely meticulous finish highlights the authenticity
of hand craftsmanship.
Bevelling is a rare and delicate art which consists in making
a polished bevel or chamfer on various parts, the rim of which
is underscored by the light playing over the bevels. There are
two possible approaches :
1) the modern method (machine bevelling)
2)
the high-end method
1) The
modern method : there are currently various modern methods
for bevelling parts :
* The
bevel or chamfer is made by machining and the polish is then achieved
chemically, mechanically or by hand with brushes.
Note : This method is satisfactory ; one can obtain a regular,
clean-cut bevel, but the angles are rounded because sharp angles
cannot be made by machine (due to the diameter of the milling-cutters).
* For large series, the bevel or chamfer is made and polished
directly by stamping.
Note : It is impossible to polish sharp angles with a brush
or mechanically. This method is satisfactory but all parts are
strictly identical, as it does not enable any degree of personalisation.
The time spent on each part is considerably reduced, implying
higher profitability, and the method does not require any particular
know-how.
2) The
high-end method, on the other hand, requires exceptional dexterity
and know-how.
Bevellers are rare, as there is no special apprenticeship for
the profession, even if certain notions of the craft are taught
in watchmaking school. To compensate for this lack, high-end watch
brands concerned with achieving the finest possible aesthetic
results (see conclusion) train their bevellers themselves.
Hand-bevelling is a meticulous operation requiring a lot of time ;
some parts may require up to 10 hours of work, resulting in high
costs that are inevitably passed on to the final products.
For all these reasons, certain companies choose the far less expensive
machine-bevelling option.
There are currently two high-end methods :
the burnisher and the wooden grinding-wheel.
a) The
burnisher method :
Preparation :
First of all, any residues or traces of machining are removed
from the flank. The latter is then smoothed by graining, as good
bevelling depends on the quality of the flank ; the aim is to
give it a smooth appearance. The surface must be clean with no
waves or imperfect shapes.
To facilitate the work of the beveller, the bevel may be blanked
by hand (with a milling-cutter) ; but the interior angles are
hollowed using a file, as no mechanical operation is capable of
making them sharp. (due to the radius of the milling-cutter).
The chamfer is then touched up by hand (*1) ; the regularity
of the width of the bevel is essential ; the edges of the angle
must remain parallel from one end to the other.
Polishing : While taking care not to create any twisting,
the perpendicular marks of the file are eliminated by straight
graining and the surface is then smoothed with a stone cut according
to the part.
Finally, increasingly fine abrasives (buffs) are used to unify
the lines, while taking care to avoid excessive rounding of the
edges and the angles* (2).
Note : irregularity and twisting are not in themselves tolerated,
except if they make the overall aesthetics more consistent.
At this stage, it is important that the part be extremely
clean, free from any residual abrasives which might scratch the
surface during the burnishing. This operation consists of cold-working
the material with a tempered steel tool in order to create a polish
* (3).
Last of all, the polishing is fine-tuned and the final radiance
is given by rubbing with a diamond paste using a wooden peg *
(4).
This traditional method is the classical method par excellence ;
it involves no limits and no constraints.
b)wooden grinding-wheel method* (5) : In this case, the preparation
is the same, but the polishing is done directly on a wooden grinding-wheel
filled with diamantine.
This technique has the advantage of being faster and offering
a high-quality result, but it calls for great mastery, as contrary
to the burnisher technique, a large quantity of matter is removed
and it is hard to make up for a mistake.
The disadvantage of this procedure is that the inside cut-outs
cannot be reached. In this case, one will tend to choose the burnisher
method in order to achieve better overall aesthetic consistency.
Conclusion :
Machine bevelling is productive and gives a clean, neat and relatively
satisfactory appearance ; however, one considers that an object
should distinguish itself by the care devoted to finishing the
smallest details, true craftsmanship bevelling appears the obvious
choice.
The “imperfections” of bevelling are tokens of hand-made authenticity
and depend on the know-how of the craftsman, implying that each
part is unique and personalised.
See: Bevelling
and finishes...(II)
..
