eciate such a large escapement model as we have been
describing, a person must see it with its great balance, nearly 4"
across, flashing and sparkling in the show window in the evening, and
the brilliant imitation ruby pallets dipping in and out of the escape
wheel. A model of this kind is far more attractive than if the entire
train were shown, the mystery of "What makes it go?" being one of the
attractions. Such a model is, further, of great value in explaining to a
customer what you mean when you say the escapement of his watch is out
of order. Any practical workman can easily make an even $100 extra in a
year by making use of such a model.

For explaining to customers an extra balance cock can be used to show
how the jewels (hole and cap) are arranged. Where the parts are as large
as they are in the model, the customer can see and understand for
himself what is necessary to be done.

It is not to be understood that our advice to purchase the jewels for an
extra balance cock conflicts with our recommending the reader not to
jewel the holes of his model. The extra cock is to be shown, not for
use, and is employed solely for explaining to a customer what is
required when a pivot or jewel is found to be broken.

HOW LARGE SCREWS ARE MADE.

The screws which hold the plates in place should have heads about 3/8"
in diameter, to be in proportion to the scale on which the balance and
escape wheel are gotten up. There is much in the manner in which the
screw heads are finished as regards the elegance of such a model. A
perfectly flat head, no matter how highly polished, does not look well,
neither does a flattened conehead, like Fig. 35. The best head for this
purpose is a cupped head with chamfered edges, as shown at Fig. 34 in
vertical section. The center _b_ is ground and polished into a perfect
concave by means of a metal ball. The face, between the lines _a a_, is
polished dead flat, and the chamfered edge _a c_ finished a trifle
convex. The flat surface at _a_ is bright, but the concave _b_ and
chamfer at _c_ are beautifully blued. For a gilt-edged, double extra
head, the chamfer at _c_ can be "snailed," that is, ground with a
suitable lap before bluing, like the stem-wind wheels on some watches.

[Illustration: Fig. 34]

[Illustration: Fig. 35]

FANCY SCREWHEADS.

There are two easy methods of removing the blue from the flat part of
the screwhead at _a_. (1) Make a special holder for the screw in the end