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making the box sides as rigid as possible, and by slightly reducing the interior
ciimensions. These precautions should always be made in standardized
^^vork, and provision made for the
taper of core prints in the boxes,
t:o avoid rubbing the taper on the
oores. Another reason why cores
Fig. 33-—The Ratchet Core in fig. 16
Fig. 34.—End Core without Ratchet in fig. 16
A, Line of joint in core.
should be made slightly below size is that, when dried, they are so hard
a.nd rigid that they retard the
shrinkage of the casting, so that
the interior either comes out
too large, or in some cases
fracture occurs unless the core
is loosened while the casting
Details of Core Formation.
—Generally this work is done
by the core makers, a class of
men apart from the moulders.
But this is merely a matter of
economy, a useful division of
tasks, since moulders can pre-
pare their own cores, and do so
frequently in the small shops.
Referring first to those cores
•which are rammed in boxes,
the work is substantially that
of dried sand moulds, with the
difference before noted, the
employment of an interior sup-
porting Skeleton, the "grid", Fig.35__ Core Box for Bevel Wheel
in place of an exterior flask.
The first thing, therefore, which has to be decided is the form and dimen-
sions of the grid. This both carries the load of sand, and affords the