s
shown in Fig. 10, in order to have the right hand free for calipering. A
short space is first turned by hand feeding, as at _D_, Fig. 7, and when
the calipers show that the diameter is slightly greater than the
finished size (to allow for a light finishing cut, either in the lathe
or grinding machine) the power feed for the carriage is engaged; the
tool then moves along the work, reducing it as at _E_. Evidently, if the
movement is along a line _b--b_, parallel with the axis _a--a_, the
diameter _d_ will be the same at all points, and a true cylindrical
piece will be turned. On the other hand, if the axis _a--a_ is inclined
one way or the other, the work will be made tapering; in fact, the
tailstock center _h_1_ can be adjusted laterally for turning tapers, but
for straight turning, both centers must be in alignment with the
carriage travel. Most lathes have lines on the stationary and movable
parts of the tailstock base which show when the centers are set for
straight turning. These lines, however, may not be absolutely correct,
and it is good practice to test the alignment of the centers before
beginning to turn. This can be done by taking trial cuts, at each end of
the work (without disturbing the tool's crosswise position), and then
comparing the diameters, or by testing the carriage travel with a true
cylindrical piece held between the centers as explained later.

[Illustration: Fig. 9. Setting Calipers by Scale--Setting by Gage--Fixed
Gage]

If the relative positions of the lathe centers are not known, the work
should be calipered as the cut progresses to see if the diameter _d_ is
the same at all points. In case the diameter gradually increases, the
tailstock center should be shifted slightly to the rear before taking
the next cut, but if the diameter gradually diminishes, the adjustment
would, of course, be made in the opposite direction. The diameter is
tested by attempting to pass the calipers over the work. When the
measuring points just touch the work as they are gently passed across
it, the diameter being turned is evidently the same as the size to which
the calipers are set.

[Illustration: Fig. 10. Views showing how the Cross-slide and Carriage
are Manipulated by Hand when Starting a Cut--View to Left, Feeding Tool
Laterally; View to Right, Feeding Tool in a Lengthwise Direction]

As the driving dog is on one end, the cut cannot be taken over the
entire length, and when the tool has arrived at say p