Why we make
this choice is based on the fact that the smaller cylinder shell gives
less friction, and the loss from "drop"--that is, side play between the
escape-wheel teeth and the cylinder--will be the same in both instances
except to change the lost motion from inside to outside drop.
In devising a system to be applied to selecting a new cylinder, we meet
the same troubles encountered throughout all watchmakers' repair work,
and chief among these are good and convenient measuring tools. But even
with perfect measuring tools we would have to exercise good judgment, as
just explained. In Chapter II we gave a rule for determining the outside
diameter of a cylinder from the diameter of the escape wheel; but such
rules and tables will, in nine instances out of ten, have to be modified
by attendant circumstances--as, for instance, the thickness of the shell
of the cylinder, which should be one-tenth of the outer diameter of the
shell, but the shell is usually thicker. A tolerably safe practical rule
and one also depending very much on the workman's good judgment is, when
the escape-wheel teeth have been shortened, to select a cylinder giving
ample clearance inside the shell to the tooth, but by no means large
enough to fill the space between the teeth.
Pages:
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323