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.
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