Section 13. qxd

Vertical boring mills
are adapted to a wide range of faceplate work that
can be revolved. The advantage lies in the ease of fastening a workpiece
to the horizontal table, which resembles a four-jaw independent chuck
with extra radial T slots, and in the lessened effect of centrifugal forces
arising from unsymmetrically balanced workpieces.
A jig-boring machine
has a single-spindle sliding head mounted over a
table adjustable longitudinally and transversely by lead screws which
roughly locate the work under the spindle. Precision setting of the table
may be obtained with end measuring rods, or it may depend only on 
the accuracy of the lead screw. These machines, made in various sizes, are
used for accurately finishing holes and surfaces in definite relation to one
another. They may use drills, rose or fluted reamers, or single-point bor-
ing tools. The latter are held in an adjustable 
boring head
by which the tool
can be moved eccentrically to change the diameter of the hole.
Precision-boring machines
may have one or more spindles operating at
high speeds for the purpose of boring to accurate dimensions such sur-
faces as wrist-pin holes in pistons and connecting-rod bushings.
Boring Recommendations
Boring recommendations for tool
materials, depth of cut, feed, and cutting speed are generally the same
as those for turning operations (see Table 13.4.4). However, tool deflec-
tions, chatter, and dimensional accuracy can be significant problems
because the boring bar has to reach the full length to be machined and
space within the workpiece may be limited. Boring bars have been
designed to dampen vibrations and reduce chatter during machining.
DRILLING
Drilling
is a commonly employed hole-making process that uses a 
drill
as a cutting tool for producing round holes of various sizes and depths.
Drilled holes may be subjected to additional operations for better sur-
face finish and dimensional accuracy, such as reaming and honing,
described later in this section.