ncorporate the parts. Care should be observed not to burn
the shellac. While warm, the melted mass is poured on to a cold slab of
iron or stone, and while plastic made into sticks about 1/2" in
diameter.

[Illustration: Fig. 178]

[Illustration: Fig. 179]

We show at Fig. 178 a side view of the outer end of a cement chuck with
a cylinder in position. We commence to turn the lower pivot of a
cylinder, allowing the pivot _z_ to rest at the apex of the hollow cone
_a_, as shown. There is something of a trick in turning such a hollow
cone and leaving no "tit" or protuberance in the center, but it is
important it should be done. A little practice will soon enable one to
master the job. A graver for this purpose should be cut to rather an
oblique point, as shown at _L_, Fig. 179. The slope of the sides to the
recess _a_, Fig. 178, should be to about forty-five degrees, making the
angle at _a_ about ninety degrees. The only way to insure perfect
accuracy of centering of a cylinder in a cement chuck is center by the
shell, which is done by cutting a piece of pegwood to a wedge shape and
letting it rest on the T-rest; then hold the edge of the pegwood to the
cylinder as the lathe revolves and the cement soft and plastic. A
cylinder so centered will be absolutely true. The outline curve at _c_,
Fig. 178, represents the surface of the cement.

The next operation is turning the pivot to the proper size to fit the
jewel. This is usually done by trial, that is, trying the pivot into the
hole in the jewel. A quicker way is to gage the hole jewel and then turn
the pivot to the right size, as measured by micrometer calipers. In some
cylinder watches the end stone stands at some distance from the outer
surface of the hole jewel; consequently, if the measurement for the
length of the pivot is taken by the tool shown at Fig. 175, the pivot
will apparently be too short. When the lower end stone is removed we
should take note if any allowance is to be made for such extra space.
The trouble which would ensue from not providing for such extra end
shake would be that the lower edge of the half shell, shown at _e_, Fig.
171, would strike the projection on which the "stalk" of the tooth is
planted. After the lower pivot is turned to fit the jewel the cylinder
is to be removed from the cement chuck and the upper part turned. The
measurements to be looked to now are, first, the entire length of the
cylinder, which is understood to be the entire