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Full text of "Modern Mechanical Engineering Vol-I"

THE   WORK  OF THE  MACHINES

213

still retained in some instances, and is fixed at the rear of the turret. The
one stop serves for every tool, so that each tool has to be adjusted by it.
This is abandoned in the better class of lathe in favour of a separate stop
adjusted to each tool. For a six-sided turret, six stops are fitted. For
turrets that have cross-traverse movements, similar stops are included to
determine diameters. The cross-slide again has its stops for the front and
back tool posts. Another kind of stop is included in the setting of the
turret tool itself. One determines the precise longitudinal position of
the bar thrust through the hollow spindle. Others, in box tools, set the

Fig. 48.—Automatic Turning Machine

length of a cut, or the throw-out of an opening die, while vee and roller
steadies fix diameters. In the screw machines the setting of the cams
determines the lengths and the diameters of cuts.

Automatic Turning Machines.—It is a remarkable fact, illustrative
of the present trend of machine-shop practice, that just as the turret lathes
and automatics have taken much work away from the common lathes, so
the turret lathes and automatics in turn are being hardly hit by other machines
possessing simpler and more restricted functions. This is largely due to the
fact that economical production requires the dividing of certain classes of
work between distinct machines. Generally heavier cutting can be done
and a larger number of tools brought into action. As a result, many lathes
are now fitted with very substantial rests for holding multiple tools. One
group, represented by several designs, is the automatic turning lathe (fig. 48).
The functions of this group are restricted, but it out-distances the turret

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