Pattern making using the traditional
sand-casting method requires that patterns of
the final shape be created. These patterns are
often constructed using wood, allowing for the
shrinkage of the metal from the liquid-poured
state to the cooled-solid state. A pattern can
be composed of the final shape pattern and
potentially numerous cores, conducive to
passageways, cavities, or even full-hollow
sections as found in pipe. The pattern becomes
the positive, and the core becomes the negative,
restricting the flow of liquid into a specific
area. To construct a cylindrical core, a core
box must be created. It becomes the mold used to
construct the core.
There are two accepted methods for using a
plane-type device to construct a channel of
semicircular cross section, creating a form for
making a round core. The first uses a V-shaped
base to ride on the sides of a roughed-out base
that replicates one-half of a cylinder. This
type of plane is worked through the arc after
the final width of the semicylinder is
calculated. The rough waste is removed
beforehand, using numerous controlled saws or a
combination of chisel cuts and small rounding
planes. The plane then rides on the two edges of
the cut slot and is rotated through the arc,
cutting the semicylinder. This was an early
method of cutting a large semicylinder.
The second method using a plane is done by
restricting the sides and creating a
swinging-blade holder that allows a fixed-sized
semicylinder to be cut. The wastage is roughed
out as described above. The length of the cutter
blade exposed from its holder controls the size
of the radius. The ratcheting movement of the
handle advances the cutter through the arc by
using a gear and a pawl. This mechanical method
was used as early as 1866. |
