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Full text of "Modern Mechanical Engineering Vol-I"


Fig. 15.—Drop or Pocket Prints

Horizontal Prints.—Round core prints disposed horizontally, as in
pipes, columns, and work of which these are typical, are not tapered. The
lengths of the prints are
about equal to their
diameter in the smaller
dimensions. As sizes in-
crease, the lengths are rela-
tively less. But they may
never be very short, because
in that case the weight of a
heavy core would cause the
sand to crush. In most
cases the core is bridged
between two horizontal
prints. When it has to be
supported from a single
print impression the length

must be sufficient to counterbalance the weight of the overhang of the
core. But this is only necessary in those cases where no assistance can
be obtained from chaplet nails.

Drop or Pocket Prints.—These
(fig. 15) are employed for horizontal
cores when the joint of the mould
does not coincide with the centre of
the core print, as it does in the pipe
and column types of patterns. Even
then in some cases round parallel
prints are attached, and a sloping
" down-joint'1 is made to the centre.

Or round, tapered prints are skewered on loosely. But these are excep-
tions to the usual practice.

The drop print only indicates a portion of the outline of the core to be
inserted — the lower part,
semicircular for round cores,
other shapes for other forms.
The portion of the print above
the centre is tapered to deliver,
but its impression is filled up,
following the insertion of the
core—" stopping-over ". This

is   done   by   the   moulder,   Or,                  F*S- i?.—Boss Facing covered with Drop Print

in standard work, the core is

made in a box (fig. 16), which includes the stopping-over portion in
addition to the actual core. The thicknesses of these prints are similar to
those of the plain horizontal kind. Thin prints will not provide sufficient
support in the sand to sustain the weight of a core without risk of crushing.

Fig. 16.—Core Box for Stopping-over Drop Prints