screw _C_, and the required center-to-center distance between the two
cylinders can be gaged by the micrometer dial _M_ on the cross-feed
screw, although positive stops are often used in preference. After the
first cylinder is bored, the dial is set to the zero position by
loosening the small knurled screw shown, and turning the dial around.
The feed screw is then rotated until the dial shows that the required
lateral adjustment is made, which locates the casting for boring the
second cylinder. The end of the casting is also faced true by a milling
cutter. Ordinarily, milling cutters are bolted directly to the spindle
sleeve _A_ on this particular machine, which gives a rigid support for
the cutter and a powerful drive.

[Illustration: Fig. 11. Cylinder turned around for Machining Valve
Seats]

The next operation is that of boring and milling the opposite end of the
cylinder. This end is turned toward the spindle (as shown in Fig. 11)
without unclamping the work or fixture, by simply turning the circular
table _T_ half way around. This table is an attachment which is clamped
to the main table for holding work that must be turned to different
positions for machining the various parts. Its position is easily
changed, and as the work remains fixed with relation to the table, the
alignment between different holes or surfaces is assured, if the table
is turned the right amount. In this case, the casting needs to be
rotated one-half a revolution or 180 degrees, and this is done by means
of angular graduations on the base of the table. The illustration shows
the casting set for boring the inlet and exhaust valve chambers. The
different cutters required for boring are mounted on one bar as shown,
and the casting is adjusted crosswise to bring each valve chamber in
position, by using the micrometer dial. The single-ended cutter _c_
forms a shallow circular recess or seat in the raised pad which
surrounds the opening. The cover joint directly back of the cylinders is
finished by milling.

[Illustration: Fig. 12. Boring Differential Gear Casing]

=Examples of Boring, Radial Facing and Milling.=--Another example of
boring, in which the circular table is used, is shown in Fig. 12. The
work _W_ is a casing for the differential gears of an automobile. It is
mounted in a fixture _F_ which is bolted to the table. The casting has
round ends, which are clamped in V-blocks, thus aligning the work. This
fixture has a guide-bushing _G_