Adam, lost wax casting is a method that’s been used since ancient
times. You can do it without the fancy vacuum pumps and centrifuges
and all. The modern tools make it more precise, more repeatable,
faster, easer, and all that. But you can do it almost entirely with
equipment you literally can build yourself. Search the Orchid
Archives for “Steam casting” to find info on the methods.
In short, it works like this:
Your wax model is invested and sprued using a cluster of small
sprues to connect the main “normal” feeder sprues to the sprue base,
and the “funnel” that the sprue base forms in the investment is
scooped out with a spoon after the investment sets to form a shallow
melting crucible shape. The cluster of small sprues then show as a
group of small holes, rather than the usual one or two large ones.
The group of small sprues (usually somewhere around 14 guage wax wire
is used) should extend only a short distance below the bottom of the
"bowl" shape before combining into the larger simpler main feeder
sprues. Instead of a vacuum to de-air the investment, simply paint on
a thin layer of investment, blowing and brushing off adhering
bubbles, before then filling the flask up. Only a few bubbles from
the main pour will again find the wax, so you should be able to avoid
most bubbles on the model. They only matter if they contact the
model, which then gives you a little cast ball of metal on the
casting, which usually is not hard to clip or file off.
You can burn out the model using a simple home made muffle furnace
that uses your kitchen stove for heat. Gas is best, but an electric
stove works too. Only do this if you’ve got a good kitchen vent fan
to exhaust the wax burnout fumes to the outside, however. The “oven
muffle” is a simple red clay (terra cotta) flower pot, which you’ve
lined first with what used to be asbestos furnace tape, but is now a
similar looking insulating fire proof tape sort of material made of
other mineral fibers. It’s used as insulation in various types of
home heating furnaces, etc, and should be available in the hardware
store. Wet it so it’s pliable in order to line the pot with it. Then
line that layer with a double layer of aluminum foil, poke a small
hole through the liners to the hole in the bottom of the flower pot.
In use, the flask goes sprue hole down right on the stove burner,
with the flower pot over the top. The pot traps the heat sufficiently
that the flask will reach the needed temperatures to fully burn out
the wax (a low orange/red glow, or around 1350 F). This burnout will
take a number of hours. When the investment is again white colored in
the “crucible” area around the sprues, you’re ready to cast.
Casting is done with a simple device, which you’ve made before hand.
It’s a metal jar lid, larger in diameter than the top of the flask,
screwed to a handle, a bit of wood dowel or the like, so the inside
of the lid now faces out. You put a thick layer of newspaper in that
opening, and get it nice and wet.
Your metal is put into the shallow crucible area of the flask, and
melted, with a tiny bit of boric acid or borax flux, with your torch.
Because the sprue holes are those small diameter things, surface
tension of the metal will keep the metal from flowing down into the
holes until you force it down. You do that, when the metal is fully
melted, by quickly bringing that wet, paper lined jar lid down
through the torch flame to press down hard over the top of the
flask. It seals with the edge of your flask, and the heat from the
flask turns some of that water very quickly into steam, which
generates pressure. That steam pressure forces the metal past it’s
surface tension, and into the mold. Hold the jar lid/handle in place
for maybe 15 seconds or so, to make sure it’s had a chance to do
it’s thing. Then, once nothing is glowing any more, drop the flask
into a bucket (metal) of water, to quench it, break out the
investment, and reveal your casting.
This method is not foolproof, but it does work, and reduces the cost
of your casting setup to mostly the explaining you have to do to your
neighbors about that burning wax smell…
Because it’s not foolproof, you may wish to practice it first, with
a quick and simple sample wax model, perhaps using silver instead of
gold. Just so you can be sure it works, etc…
Email or ask on the list if you have questions.
Peter Rowe