Vacuum isn’t vastly safer than a centrifugal machine. The Neycraft
machines come in their own shields, but the standard procedure with
the ‘classic’ style is to put them in some sort of shield as well,
so all the centro machines are guarded in one way or another. Mine
is buried a foot deep in a 55 gallon steel drum, while the one I
used at school for years was in a commercial shield that worked
quite nicely. (From Otto Frei. Look for the blue octagonal shield
thing they sell right next to the ‘classic’ casting machine.)
The advantage of centrifugal machines for small, one-off castings is
that (A) you can use smaller flasks, and (B) they hit much harder,
so they can drive the metal down into very small details. My
experience with them says that you get better metal density, or
certainly better castings. As you get bigger, you get into the range
where you really don’t want that much metal spinning around the
shop. I once worked for a guy who had a home-built spin caster that
could handle a couple of pounds of bronze. that thing made you sit
up and pay attention. Never had a blowout that I know of. Because we
all paid very, very careful attention to what we were doing when it
got that big.
The big, huge, incredibly important thing is not to be afraid of
anything you’re doing. I’ve lost track of the number of times I’ve
seen someone get hurt because they let their fear get in the way,
and that caused the accident.
Sometimes the best cure for fear is understanding. Make a list of
all the things that you think can go wrong with a procedure, and
then figure out “what next?”
So you’ve got a spin caster and the metal blows out through the back
of the flask. (it happens.) What next?
It sprays off the back plate of the casting machine, and dumps into
the safety shield. Other than scaring the hell out of you, nothing
all that radical. (Most machines are rigged such that if there is
a blowout, it happens in a part of the cycle that throws the spray
away from the operator.) You get to pick a lot of very small grains
of metal out of your safety shield. Oh goody. You still want to be
wearing an apron and safety glasses though.
So you’ve got a vacuum, and you pour and miss. What happens next?
Molten metal on the top deck of the machine. Probably doesn’t stay
molten much longer than it’d take to get down to the tabletop.
Which it promptly sets on fire. Where’s your bucket of water? (I
usually keep a 5 gallon bucket of water near the casting gear to
blow out my flasks in. In a pinch, that’s the first thing I grab.
Yeah, it’ll make one hell of a mess, but much less than a fire.)
Just work through all the ‘what happens next?’ steps for every
disaster you can think of. Then do what you can to head them all off
first. And plan your responses for the rest.
The vac caster we had at school was on a stainless steel baking
tray, specifically so if it did somehow dump a bunch of molten
metal, it still wouldn’t get to the table (or over the side, onto
somebody’s toes.) We did what we could to disaster proof the gear
before anything went wrong. Because when it does all drop in the
pot, you don’t have time to think. You have to react, more-or-less
instinctively. So it’s up to you to program those instincts first.
Whatever you do, do not let your fear get in the way. That will
get you hurt. Take a deep breath, understand what’s going on, then
do your art.