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Presently: Bevelling and finishes in top-of-the-range watchmaking (VII)

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The author

Having acquired an educational background in economics and literature, Caroline Sermier fell in love with watchmaking right from her arrival at Renaud & Papi.
Her current responsibilities as head of the communication department allows her to blend a taste for writing with her fascination for complicated watches, and particularly for the finishing and decorative details on top-of-the-range luxury watches.

18. Bevelling and finishes in top-of-the-range watchmaking (VII): Wheels and pinions

 

 


Wheels and pinions
Preamble

Légende:
A) Centre wheel and pinion
B) Wheel Pinion
C) Wheel tooth
D) Leaf (tooth) of a pinion
E) Arm of the wheel
F) Wheel face or felly
G) Bevelling on the arms (hatching)
H) Chamfer sinks
I) Pinion undercut
J) Pinion face
K) Pivot

The wheel (A)
Definition : the wheel is a circular organ revolving around an axis, whose function is to transmit force. The wheel is fixed to the pinion, thereby forming the "mobile" or wheel and pinion.
The arms of the wheel (E) : they are optional ; there are five of them which lighten the wheel in order to reduce inertia and thus enhance the efficiency of the watch (eg for the base movement. Conversely, for a striking-train where one requires more inertia, the wheels will not be hollowed out.
Nota bene : to lighten a wheel, one may also cut out motifs in the matter (eg. clock wheel)
Bevelling on the arms (G) : exclusively for high-end watches, the arms are bevelled directly during stamping or filed by hand for a more traditional method
The visible face (F) of the wheels is circular-grained in the high-end and medium-range segments. It is sandblasted for low-end products.
The chamfer sink (H) : exclusively in high-end watches, since serves a purely aesthetic purpose, it is made using a diamond on the boss of the wheel in order to reflect the leaves of the pinion.
The wheel-teeth ( C ) : The first wheels were in iron and cut out with a file Today, they are in brass and are shaped by cutting

The pinion (B)
Definition : it is a toothed organ in hardened and blue-tempered steel. The pinion divides, displaces, returns, re-divides, re-displaces…
The pinion, an indispensable component in the smooth running of the watch, is made up of various parts :
- the leaves (D) of the pinion may be polished using a fine-grained soft-wood disc for the traditional method, or more commonly in the tumbling-barrel for larger series. Polishing the pinion leaves considerably reduces friction and thus enhances energy transmission
- the faces (D) of the pinion leaves are flat-polished for obvious aesthetic reasons. This operation gives a special shine which is reflected on the wheel and creates a luminous effect which embellishes the wheel and pinion as a whole.
- the undercut (I) : to form the pivot shoulder but also to prevent oil from reaching the face of the pinion (particularly when it is close to the jewel hole), a small notch with a triangular section is made with the burin. This circular groove also serves to keep the face flat during polishing. In former days, watchmakers used to devote particular care to the execution of extremely fine and deep undercuts.
Conclusion : all movements comprise a certain number of gear-trains in order to ensure transmission of the force and movement. These marvellous gear-trains, indispensable to the smooth running of the watch, deserve a closer look at the care devoted to their finishing; for while some simply want it to work, others also demand that it be beautiful. Légendes: Undercut for flat-based leaves Undercut for round-based leaves Variation of undercut for round-based leaves

Finishing the wheels
The method :
The procedure for making wheels is as follows :
1) cutting out the small discs
2) decoration and finishing
3) colouring or electroplating
4) cutting teeth
5) assembling with the pinion
Only the points relating to the finish and the decoration (2,3) are examined here.

2 : Decorations and finishing

Bevelling the arms : (photo 2) Can be done directly when cutting out by stamping. The result is satisfactory, but in high-end watches, the bevelling on the arm may be touched up with a file.
They may then be given even more radiance by finishing them with a polish using the burnisher in the traditional manner (see article : high-end bevelling, the methodology).
- the chamfer sink : for purely decorative purposes, a chamfer sink will be created with a diamond on the hub of the wheel.
-circular-graining : (photo 1) : the wheels are generally circular-grained on their visible side in a watch movement. Circular-graining involves smoothing the wheel face with a stick of water-of-ayr stone or a buff. The wheel turns and the stick of water-of-ayr stone is pressed against the face. This kind of finish makes fine circular marks and enhances radiance.
Nota bene : when the milling-cutter has left burrs on the side where the teeth start, they may be removed using a flat water-of-ayr stone. The inner felly may also be touched up with a sage-leaf shaped file adapted to the curve.
- sunray-brushing : (photo 3) : Generally used on steel wheels, this type of decoration achieved using a bell-shaped grinding-wheel makes marks resembling the rays of the sun

3. Colouring or electroplating : (photo 4)
This procedure consists of depositing a fine layer of another metal (nickel, gold, rhodium) on the metal surface .
The primary purpose of this coating is aesthetic, but it also protects from oxidation. For example, gold-plating protects and improves the appearance of brass parts which tend to become dull quite quickly. There are various shades of colours, ranging from the most yellow (1N) to the reddest (5N).
The surface must first be prepared by meticulous polishing, since the gold-plating will cover the surface without modifying its texture and without hiding any remaining flaws.
Nota bene: cutting the teeth (cutting tooth by tooth or hobbing) is the last operation performed in order to avoid gold-plating deposits on the profile of the toothing.

Conclusion: One may state that stamping or hobbing are the methods almost systematically for machining wheels, since they give very satisfactory results in terms of quality and do not necessarily require touching up in terms of finish. Nonetheless, in the high-end market, the expert hand of the craftsman will always be able to fine-tune the finish, if only for the inherent beauty of these skilled gestures.

Finishing the pinions:
The method:

The procedure for making pinions is as follows:
1. profile-turning: a) industrial machine or b) on the polishing lathe
2. cutting a) by hobbing or b) tooth by tooth
3. Thermal treatment
4. Burnishing the pivots a) using a bow or b) a grinding-wheel
5. Finishing and decoration
a) polishing the leaves : 2 methods
b) polishing the faces of the pinion leaves: 2 methods
c) polishing the pivot-shanks : 2 methods
d) polishing the undercuts: 2 methods
Only the points relating to decoration (4 and 5) will be examined here.

4. Burnishing : is performed on the pivots. This is a polishing operation performed using a burnisher. This operation enables one to achieve the definitive dimensions, while considerably enhancing the state of the surfaces on both functional and aesthetic levels.
- traditional method: for delicate hand-made operations, burnishing will be done on a bow with a burnisher. The pivot rests in a notch of the runner of the Jacot tool. The burnisher presses against the pivot while it turns (photo 5)
- industrial method: for large series, the polishing lathe or carbide grinding-wheel greatly facilitates the task. In this case, the burnishing disc is lowered while it is rotating until the desired diameter of the pivot is reached (photo of burnishing lathe). A well polished pivot will be exempt from marks or scratches on its surface.

5. Finishing and decoration
a) polishing the pinion leaves: 2 methods
- traditional method:
the pinion leaves are polished with a fine-grain soft-wood disc. The wooden disc (generally in pearwood) is fitted to a runner with a pully driving it. The pinion turns under the disc at less than 90° of its axis. During polishing, the pinion is moved to and fro on its axis so as to polish the entire length of the leaves. - The disc is coated with an extremely fine polishing mixture which removes any marks of machining. This pinion polishing operation is performed quickly, providing it has been correctly prepared.
Nota bene: it is essential not to overly reduce the pinion diameter.
- industrial method (photo 7): the pinion leaves may also be polished in the tumbler-barrel (also known as tumbling). In this case, the parts to be polished are placed in a small tumbler containing grains and various abrasive substances; the tumbler, placed on a shaft, rotates and thereby polishing all surfaces of the part by rubbing.
b) Polishing the faces of the pinion-leaves¨ 2 methods:
- traditional method
: the faces of the pinion leaves are polished with diamantine on bronze or zinc pads, after being smoothed down. The polishing may be done in a more suitable manner with a bow, suing the wheel to drive it. It is essential that the face of the pinion should not lose its flat contact with the pad (photo 6 and 8).
- Industrial method: in the tumbling-barrel (see above).
c) Polishing the pivot-shanks: 2 methods
- traditional method:
the pinion is fixed to a lathe and the craftsman polishes the surface of the pivot-shank using an abrasive fixed to a peg (photo 8)
- industrial method: in a tumbling-barrel (see above)
d) Polishing the undercuts: 2 methods
- traditional method:
particularly meticulous in the high-end segment, polishing the undercuts prevents the oil from reaching the face of the pinion. This surface state is achieved using a flange coated with diamantine and adapted to the particular shape of the undercut.
- industrial method: in a tumbling-barrel (see above).

Conclusion: Most finishing flaws stem from poor preparation. It is thus essential that the pinion be properly machined if one wishes to achieve a scratch-free, soft and flat surface. In certain cases, polishing may also be done on all parts of the pinion. This operation will create a state of brilliance which will embellish the wheel and pinion in its entirety (photo 8).




See: Bevelling and finishes...(VI)

 













Machine à polir les pignons


 

   

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