plate miscasting (was "Fixing Plates"

[Frank Emerson]

> Would the model and length designation would be a separate part of  
> the pattern in the moulding process?

Some foundries stick on a series of numbers on the bottom side of the plate
pattern to produce a code representing a batch number or the date the plate
was cast.  The next day, they scrap of the numbers and stick on new ones. 
This code will never see the light of day, until a rebuilder removes the
plate and exposes the bottom-side.   In the early days of a new model the
pattern may be made of wood with a "ton" of bondo or epoxy filler. 
Eventually, after all the "bugs" are worked out, a pattern will be made of
a more permanent material.

> Or is a plate pattern simply two  
> large plate-sized pieces, top and bottom? (I don't know much about  
> the mechanics of plate casting).

A plate pattern looks pretty much like the finished plate, dimensionally,
except that it is scaled up, about 1' 1/8" to 1', to allow for the
shrinkage of the plate as it cools.  In areas where the finished plate will
have an internal void, the pattern will have a chunk of material that will
be filled in with a "core box" later.  The pattern is pressed into a bed of
sand to form the bottom half of the mold.  A wooden frame, reinforced with
a wire lattice is placed on top.  Sand is poured into this form.  The sand
has a black coagulant to make it stick together well, when packed.  Once
the sand is tightly packed around the pattern, the top section can be
lifted off, and the pattern removed.  The top and bottom halves of the mold
are called the cope and drag, respectively.  The core box(es) are
strategically positioned to prevent the iron from flowing into the internal
void areas.  The cope is replaced over the drag, and you have a temporary
mold in which to pour the molten iron.  There are more efficient methods
for mass production, but the method described is still widely used.

Frank Emerson
pianoguru at earthlink.net