120, 100, 90, 80, 70, 60, 54,
46, 40. For large work roughly filed, use coarse cloth such as Nos. 46
or 54, and then finer grades to obtain the required polish. If the work
has been carefully filed, a good polish can be obtained with Nos. 60 and
90 cloth, and a brilliant polish by finishing with No. 120 and
flour-emery.

Most cylindrical parts can be finished more quickly and accurately in
the grinder than in the lathe, and many classes of work are, at the
present time, simply rough-turned in the lathe and then ground to size
in a cylindrical grinding machine.

=Aligning Centers for Cylindrical Turning.=--When a rod or shaft must be
turned cylindrical or to the same diameter throughout its entire length,
it is good practice to test the alignment of the centers, before
inserting the work. The position of the tailstock center for cylindrical
turning may be indicated by the coincidence of graduation marks on the
base, but if accuracy is necessary, the relative position of the two
centers should be determined in a more positive way. A very simple and
convenient method of testing the alignment is shown at _A_ in Fig. 12.
The work is first turned for a short distance, near the dogged end, as
shown, and the tool is left as set for this cut; then the tailstock
center is withdrawn and the work is moved sufficiently to permit running
the tool back to the tailstock end without changing its original
setting. A short cut is then taken at this end and the diameters _d_ and
_d_{1}_ are carefully compared. In case there is any variation, the
tailstock center is adjusted laterally, other trial cuts are taken, and
the test repeated.

Another method is illustrated at _B_, which requires the use of a
test-bar _t_. This bar should have accurately made centers and the ends
finished to exactly the same diameter. The lathe centers are aligned by
placing the bar between them and then testing the position of the ends.
This can be done by comparing each end with a tool held in the toolpost
and moved from one to the other by shifting the carriage, but a better
method is to clamp a test indicator _i_ in the toolpost and bring it in
contact with first one end of the bar and then the other. If the dial
does not register the same at each end, it shows that the lathe centers
are not in line. Even when centers are correctly set, lathes that have
been in use a long time do not always turn cylindrical or straight,
because if the ways that guide the ca