Hello Kathy, I have done several large casting projects in sterling
and some in gold.
Large objects require a large spruing system and a large button,
usually about three times the weight of the piece. They also require a
very cool casting temp. They can be done with a vac or a centrifuge
With very large pieces, I will usually reinforce the investment
using fiberglass. this is so the investment doesn't explode when a
pound or two of silver hits it.
My machinist has created large, thick and odd shape mold frames to
meet about any molding situation. I prefer natural rubber for most
molds unless I need to minimize shrinkage. If an object is too large
for my mold frames, I make an RTV mold in a custom made box using a
two part system so I don't have to cut a mold that big.
Getting a good wax can often be a greater challenge than casting on
an oversize piece. On a piece that is very large I use injection
times up to 5 mins, not just to fill the mold, but to keep pressure
on the wax as it is drawing and cooling. I have cobbed together some
pretty weird clamping systems to hold large molds together and in
place while injecting.
Finishing a large casting is also a challenge. I would usually opt
for a piece with lots of texture as opposed to a high polish.
The cost of the silver is less than the labor for such pieces.
Removing weight in the injected wax is not a bad idea if it improves
the casting propertiecs of the model. The customer may want the extra
weight. Maybe you could hide one of those "Abforce" things in the
back of the buckle to strengthen his stomach while he's wearing
it!......Hope some of this helps.
John, J.A.Henkel Co., Inc., Moldmaking, Casting, Finishing and
producing solutions for jewelry artists.