Errr..I'll try to put this all gently, but focus on the wax ring.
Get that exactly the way you want it, then send it out for casting.
There are plenty of firms in the UK that specialize in job casting.
Trying to wing it yourself with the gear you've mentioned is a
recipe for disaster on a wedding ring. If you had more time, and
more chances to experiment, you could use those to learn and refine
your technique. Trying to go from a standing start right into a
wedding ring straight out of the gate isn't likely to end in
anything but very expensive gold tears.
I'll take your points in order, but trust me on this one: look for a
job caster. It'll still be your ring, you'll have to do all the
finishing, but they'll do the bit you don't have the kit for. Much
safer and more likely to work.
I know you want to do it all yourself, but many of us on Orchid have
seen this movie before. You're not the first to try this. It doesn't
1) no vacuum chamber. Can be overcome (more or less) by intense
vibration of the flask for a minute or two after you pour it. You'll
have to build some sort of a vibrating table rig, but this can be
done. You'll still likely have air bubbles, but probably not enough
to junk the ring.
2) roughly 670-700 degrees centigrade. Well beyond anything an oven
can do. You're talking kiln here. That's max temp to make sure the
carbon's gone. Final casting temp should be around 510-525 C. Still
well out of oven range, and it needs to be brought up gradually over
a couple of hours. Not something you're going to do with bricks and
a blowtorch. (I think in Fahrenheit, so those values are ballpark.)
3) plumber's blowtorch. Depends on what you mean by a plumber's
torch, but the probable answer is no.
If you're talking about one of those torches where a torch tip
screws right onto a tank of compressed fuel, then no, you can't do
much more than melt little rings of your chain. You might be able to
get bits of it molten, but probably not the whole thing, all at
once. By the by, what do you plan to melt the gold in? You'll need a
crucible and flux, as well as a more powerful torch. (As well as
more gold than you think you'll need. There are sprues to fill too.
And chains tend to have all sorts of nasty things mixed in with them
that mean that they tend not to cast well when remelted...) (they're
still the right karat, but they tend to have solder built into the
wire itself to make it easy to solder them together. The solder
fouls the alloy for casting.)
4) Do *NOT* use a router to power a centrifuge unless you find some
way to gear it *WAY* down!
Better thought: just don't use a motor. Period. Way too fast, and
likely to tear itself apart.explosively.
Most small centrifuges are spring powered. They start off pretty
quick, but then coast and spin down after the spring uncoils. Max
RPM is probably somewhere well below 300 rpm, even at launch.
Balance is a real issue with pounds of flask and metal spinning
around like that. Get the balance wrong, and the best thing that
happens is that it lurches around the room like a drunk washing
machine. Don't ask about the worst case.
There are motor powered ones, but they're big industrial units,
built by people who know what they're up to, with serious interlocks
and blast shields to prevent or contain catastrophic failures. It
should tell you something that the real ones all come with blast
shields to contain the inevitable shattered molds and flying bits of
Absent a real centrifuge, there are better ways to do lost wax:
steam casting comes to mind. Much safer, with almost no kit needed.
(once you manage to burn out the flask and melt the metal. See
problems 2 & 3 above. That still remains.)
Delft clay is designed for a slightly different process, so it works
differently. It also doesn't give quite the resolution of investment
casting, and can't handle undercuts the way that investment casting
can. For the best resolution of the mold details (from the wax) you
need more force on the metal than you'd get by just pouring it in.
Thus the centrifuge or other casting method.
After re-reading this, I have a suggestion: find a copy of Tim
McCreight's _The Complete Metalsmith_. Read the sections on casting.
Alternately, find a copy of his book _Practical Casting_. Either one
of them will explain the casting process in much more detail.
I know you want to do it all yourself, and I know it's important to
you, but please believe me when I say you're better off finding a job
shop to handle the casting. It'll probably be cheaper in the long run
too, given all the kit you'll have to buy to even make a stab at
doing it yourself.
Work on the wax model. That's the part that's really yours. The
casting is just a process. Done right, it's pretty mechanical. The
final finishing will have more to say about what it looks like than
the casting should, if done right. So you can say that you did all
the parts that matter. (when you find a job caster, talk to him
about how to make the ring in such a way that it casts right. There
are tricks to that too.)
Best of luck, and congrats.