struction are built in many different sizes. The main spindle of the
machine illustrated is driven by a motor located at the rear of the
vertical column _C_, the motion being transmitted to the spindle through
shafts and gearing. The casting _D_, shown in this particular
illustration, is for a steam engine of the horizontal type, and the
operation is that of boring the cylindrical guides or bearings for the
crosshead. These bearings have a diameter of 15-3/4 inches and are
37-3/4 inches long. In boring them, two roughing cuts and one finishing
cut are taken. The end of the casting, which in the assembled engine
bears against the cylinder, is then faced by means of a regular facing
arm.

After removing the boring-bar the table _E_ of the special fixture on
which the casting is mounted is turned one quarter of a revolution. A
large milling cutter 24 inches in diameter is next mounted on the
spindle of the machine, and one side of the main bearing, as well as the
pads for the valve-rod guide-bar brackets, are milled. The table is then
revolved and the opposite side of the main bearing is milled in the same
way, the table being accurately located in the different positions by an
index plunger _F_ which engages holes on the under side. The spindle is
now moved upward to allow the table to be turned so as to locate the
bearing end of the frame next to the headstock of the machine. The
milling cutter is then used to machine the inside and top surfaces of
the main bearing. By turning the fixture and not changing the position
of the casting after it is bolted into place, the various surfaces are
machined in the correct relation to one another without difficulty. This
is a good example of the work done on horizontal boring machines of the
floor type.

INDEX

PAGE

Acme flat turret lathe, examples of chuck work 219
Acme standard thread and tool for cutting 159
Acme standard thread gage 157
Acme thread tool, measuring width with vernier caliper 157, 158
Accumulation of errors 105, 106
Aligning lathe centers for cylindrical turning 16
Allowances, average, for forced fits 130
for different classes of fits 131
for driving fits