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THE  WORK OF THE  MACHINES                 219

Capacities range from J to 4! in. diameter in steel, and from 4 to 6 in.
diameter in cast iron. A i-in drill can be fed in steel at the rate of 14! in.
per minute, a i-in. drill in cast iron at the rate of 24 in. per minute.

Fig. 53 shows one of the Asquith radial machines, electrically driven,
having a central thrust to the spindle. The firm's universal tilting table is
a valuable adjunct, since it enables each side of a piece of work (except that
in contact with the table) to be machined at a single setting. The table pivots
through a complete circle on trunnions, and carries two independent tables
on opposite faces, each of which can be given a rotary movement by hand.
These tables have tee-grooves for the attachment of work. Drilling, reaming,
and facing can be done at different angles.

At present, opinion is divided concerning the best uses to which single-
spindle machines disposed in gangs, or multi-spindle machines, may be put.
The spindles are disposed in gangs, or in clusters. Fig. 54 shows a highly
specialized design to deal with work to be machined from three faces, without
resetting it. The machine shown is by the National Automatic Tool Company
of Richmond, Indiana. Many of the multi-spindle tools have been evolved
for motor work, for drilling crank cases, cylinders, gear cases, cylinder heads,
connecting rods, &c. They produce a large number of holes simultaneously
instead of singly. They also ream, counterbore, and face the holes.

Boring Machines.The difference between a machine that drills and
one that bores is that the latter deals with larger holes, which fact influences
the design and the operating mechanism. Though in very many machines
boring is included with drilling, only holes of small diameters and of moderate                            {
lengths can be bored in these machines.    Since these machines are for                            J
general purposes, tapping, facing, and often milling are included.   Here a                            *
large range of speeds and feeds is essential.    A modern machine of this                            ^
class will have as many as eighteen spindle speeds, ranging from 7 or 8 r.p.m.                            }
to 200 or 250 r.p.m., and say nine feeds, which, given in inches per revolu-                            j
tion of the spindle, range from 0-006 in. or 0-007 in. to 0-115 in. per                            |
revolution.    If tapping and milling are not included the range need not be
so extensive.
An excellent example of a horizontal-spindle design is the " Pearn-
Richards " combined machine, the functions of which include drilling, boring,
tapping, surfacing, milling, and, with a suitable attachment, screw-cutting.
Thirty-two variations in speed are provided, and eight rates of feed, applicable
to the longitudinal, transverse, and vertical slide movements. The illustra-
tions are nearly self-explanatory. The machine is manufactured by Messrs.
Frank Pearn & Co., Ltd., Manchester.
Fig. 55 shows one of the Crossley gas-engine beds being bored and faced
with tandem cutters in the bar. The bar is driven from the head and sup-
ported in the hinged bearing on the stay at the right hand. The square table