THE BALANCE COCK
BY WALT ODETS
 The
balance cock (a cock is a bridge secured to the movement
plate at only one end) is shown for all three movements in
an inverted position. While the upper surfaces resemble the
surfaces of the wheel train bridge, the undersides of the cocks
tell us something about both their construction and finish. The
JLC cock (2A) is very well finished, and the end of the
cock (yellow arrow), which carries the upper balance pivot,
is carefully machined for balance shaft end play and parallelism
with the plate (which supports the lower balance pivot). The
cap jewel assembly (this movement provided no shock protection)
is attached with two screws (green arrow). The base of
the cock is located with three pins (blue arrows)
for correct alignment with the main plate. A screwdriver access,
to loosen the cock without gouging it or the plate, is provided
(white arrow). The hairspring stud (red arrow)
is robust, assuring stability in this important attachment. (Any
change in the outer attachment of the spring would destroy the
timing of the watch.)
 The
Eterna balance cock (2B) is nearly as well finished (on
this side) as the JLC cock. The balance end of the cock is machined
with the entire arm of the cock. A U-shaped, steel clip is used
to fasten the balance cap jewel (and shock protection), the channel
for which is indicated at the blue arrow. The cock is
located with two pins, and no screw driver access is provided.
The hairspring stud is provided as an appendage of the regulator
ring (removed in the illustration), a much less rigid design
than the JLC arrangement, but offering the possibility of an adjustable
stud.
 The
Tissot cock (2C) is basic. Located with two pins, the
cap jewel assembly is retained by a friction fit. The projection
of the assembly below the surface of the cock (yellow arrow)
suggests that the friction positioning of the assembly--rather
than precise machining of the cock--were used to set balance
shaft end play. The bottom of the bridge foot is partly finished
with crude perlage, a pattern of over-lapping circles
(blue arrow). This was probably done to minimize rough
machining rather than to enhance a properly finished surface.
As this surface mates to the main plate and determines the alignment
of the entire cock, perlage is not the correct solution.
|
