THE LOVELY BLANCPAIN 1106
GETS A NEW BACK

PART 2

BY WALT ODETS















I have recently begun using a new Bergeon Lathe B, purchased through Bob Frei of the TimeZone Tool Shop. Swiss made, this is a
very traditional watchmakers lathe of excellent precision and versatility. The feel and aesthetics of the lathe are lovely. The only modern touch is a digitally controlled, constant torque drive
(seen back, right).







































































With the exception of a few other very small projects, the 1106 back modification would be the B’s maiden voyage.

As illustrated
left, the back is first mounted in a universal, outside-gripping, self-centering chuck
(1). A slide rest (2) with multiple-cutter tool post
(3) mounted on top is
used. The first cut will remove the center of the back.

During the first cut.


The first cut complete. Note that although the center section has a beveled edge, the cut on the ring side is vertical. The
opening in the ring is 26 millimeters in diameter.





















A lip to support the crystal is cut next. For this purpose, a “separating” graver is used, with a cutting
edge parallel to the rotation of the work. The sapphire crystal will be 27 millimeters in diameter, providing a 0.5 millimeter lip around the circumference.






During cutting, the slide rest carrying the tool post may be advanced in
one-hundredths of a millimeter. This provides excellent control of the depth
of this critical cut.




Results after the second cut.

























































































A series of finishing operations are performed next. These are accomplished with India stone dust mixed with oil, on shaped
peg wood
sticks. The work is rotated at higher speed than during cutting. A minimum of material is removed and the edges are preserved.



Finishing the outside surface.


With the work rotating at very
low speed, a brushed finish is applied with Bergeon medium-grade “polishing material,” an abrasive-impregnated rubber block.
























With yet another graver, a decorative groove, to reflect the design of the bezel, is cut in the outside
surface of the back.




To contrast with the brushed surface, the groove is spun to a high polish. Jewelers
rouge mixed with oil is used on the end of a piece of
pegwood.





The back is now finished. The 0.8
mm thick sapphire crystal will be fixed with a Seiko crystal epoxy. This provides a lower profile than a pressure gasket, an excellent seal, and a more rigid construction.
































































The results provide a pleasing watch to wear, and one that allows admiration of the craft from F. Piguet within.











RETURN TO PART 1 OF THE ARTICLE


 
© 2012 Bourne In Time Inc.