heating and hardening. A paste made of castile soap and water applied to
the regulator bar in the iron envelope will protect it from oxidizing
much during the heating. The portions of the regulator bar marked _h_
are intended to be rounded, while the parts marked _m_ are intended to
be dead flat. The rounding is carefully done, first with a file and
finished with emery paper. The outer edge of the loop _A''_ is a little
rounded, also the inner edge next the cap _C_. This will be understood
by inspecting Fig. 46, where we show a magnified vertical section of the
regulator on line _l_, Fig. 40. The curvature should embrace that
portion of _A''_ between the radial lines _o o'_, and should, on the
model, not measure more than 1/40". It will be seen that the curved
surface of the regulator is sunk so it meets only the vertical edge of
the loop _A''_. For the average workman, polishing the flat parts _m_ is
the most difficult to do, and for this reason we will give entire
details. It is to be expected that the regulator bar will spring a
little in hardening, but if only a little we need pay no attention to
it.

[Illustration: Fig. 44]

[Illustration: Fig. 45]

[Illustration: Fig. 46]


HOW FLAT STEEL POLISHING IS DONE.

Polishing a regulator bar for a large model, such as we are building, is
only a heavy job of flat steel work, a little larger but no more
difficult than to polish a regulator for a sixteen-size watch. We would