but its construction is
quite different, as will be seen. The spindle cannot be adjusted
vertically as with the first design described, but it is mounted and
driven very much like the spindle of a lathe, and adjustment for height
is obtained by raising or lowering the work table. The design is just
the reverse, in this respect, of the machine shown in Fig. 1, which has
a vertical adjustment for the spindle, and a work table that remains in
the same horizontal plane. The raising or lowering of the table is
effected by shaft _E_, which rotates large nuts engaging the screws _S_.
Shaft _E_ is turned either by hand or power.

[Illustration: Fig. 2. Horizontal Boring and Drilling Machine with
Vertical Table Adjustment]

The main spindle is driven by a cone pulley _P_, either directly, or
indirectly through the back-gears shown. This arrangement gives six
spindle speeds, and double this number is obtained by using a two-speed
countershaft overhead. The motion for feeding the spindle longitudinally
is transmitted through a cone of gears, which gives the required
changes, to a pinion meshing with a rack which traverses the spindle.
The large handwheel _H_ and a corresponding wheel on the opposite side
are used for adjusting the spindle rapidly by hand. The yoke or outboard
bearing _B_ for the boring-bars can be clamped in any position along the
bed for supporting the bar as close to the work as possible.

Horizontal boring machines are built in many other designs, but they all
have the same general arrangement as the machines illustrated and
operate on the same principle, with the exception of special types
intended for handling certain classes of work exclusively. The
horizontal boring, drilling and milling machine is very efficient for
certain classes of work because it enables all the machining operations
on some parts to be completed at one setting. To illustrate, a casting
which requires drilling, boring and milling at different places, can
often be finished without disturbing its position on the platen after it
is clamped in place. Frequently a comparatively small surface needs to
be milled after a part has been bored. If this milling operation can be
performed while the work is set up for boring, accurate results will be
obtained (provided the machine is in good condition) and the time saved
that would otherwise be required for re-setting the part on another
machine. Some examples of work on which different operations