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.