rriage, and the boring-bar is rotated by the lathe
spindle. The tool-head of this boring-bar carries two tools located 180
degrees apart and it is fed along the bar by a star-feed mechanism shown
attached to the bar and the tailstock spindle. Each time the bar
revolves, the star wheel strikes a stationary pin and turns the
feed-screw which, as the illustration shows, extends along a groove cut
in one side of the bar. This feed-screw passes through a nut attached to
the tool-head so that the latter is slowly fed through the bore. When
using a bar of this type, the carriage, of course, remains stationary.

[Illustration: Fig. 46. Boring a Cylinder Lining in an Ordinary Engine
Lathe]

Cylindrical parts attached to the carriage can also be bored by using a
plain solid bar mounted between the centers. The bar must be provided
with a cutter for small holes or a tool-head for larger diameters
(preferably holding two or more tools) and the boring is done by
feeding the carriage along the bed by using the regular power feed of
the lathe. A symmetrically shaped casting like a bushing or lining is
often held upon wooden blocks bolted across the carriage. These are
first cut away to form a circular seat of the required radius, by using
the boring-bar and a special tool having a thin curved edge. The casting
is then clamped upon these blocks by the use of straps and bolts, and if
the curved seats were cut to the correct radius, the work will be
located concentric with the boring-bar. When using a boring-bar of this
type, the bar must be long enough to allow the part being bored to feed
from one side of the cutter-head to the other, the cutter-head being
approximately in a central location.

[Illustration: Fig. 47. Method of Setting Circle on Work Concentric with
Lathe Spindle]

=Boring Holes to a Given Center Distance.=--In connection with faceplate
work, it is often necessary to bore two or more holes at a given
distance apart. The best method of doing this may depend upon the
accuracy required. For ordinary work sometimes two or more circles _A_
and _B_ (Fig. 47) are drawn upon the part to be bored, in the position
for the holes; the piece is then clamped to the faceplate and one of the
circles is centered with the lathe spindle by testing it with a pointer
C held in the toolpost; that is, when the pointer follows the circle as
the work is turned, evidently the circle is concentric with the spindle.
The hole is then drilled an