Hi Ken,
A 10 CFM pump will be more than enough for a vacuum casting rig, and
will probably work just fine for investing as well. (10 CFM is plenty
of flow, but the real question for investing is ultimate vacuum. If
it’ll boil water (>29inHg) you’re good.)
Your basic casting table rig is a flat plate with a hole in the
center (1/2" pipe). (Plus silicone sealing gasket) Have the pipe
come straight down from the table, past a “T” joint, with another
3-4" stub of pipe continuing straight down. Cap the stub, and then
take your vacuum line off the side of the “T” joint. The idea with
the stub is that way if you get a flask that cracks, and allows metal
to blow thru, it drops straight down into the stub, (where you can
retrieve it) rather than either melting your vac line, or worse,
getting sucked into the pump. With that in mind, make sure you put
some sort of particulate/oil filter on the vac line, just to make
sure. (You’d be amazed how far down the line little blobs of molten
metal can go…)
Investing tables are almost the same: big flat plate. Up on springs
this time, so you can shake it. The vac hookup is a little different
as well. Rio (and probably others) sell bell jars that have side
draw fittings, so you can hook the vac line up to the side of the
jar. For quick and dirty, this is great. At that stage, all you need
is a plate of 1/4" 6061-T6 aluminum, and a rubber sheet to cover it.
(plus the corner springs) If you want to use a non-side draw bell jar
(most of them) you need to rig a bottom draw fitting. This is
essentially a bit of pipe that comes through the bottom plate,
towards the rear of where the bell jar sits, so it’s out of the way.
Rig it so that it comes through the plate, and then ends up an inch
or so in the air. The idea being if any investment spills, the vac
inlet is up in the air, so it doesn’t suck the investment right into
the pump. (Investment in your pump is a real problem.) The two I’ve
made have both had machined “mushroom” pipe caps on them, so that the
draw comes in from the bottom side of a large overhang. That way
there’s no way random flying investment bits (and there will be some)
will get sucked straight down into the pump. I’ve also seen people
use brass pipe caps, and drill holes through the sides of them to
allow the air through. The critical idea is to get the inlet up off
the tabletop, and to protect it from splashed investment. However you
do that will probably be fine.
Hope that helps. I’d definitely try to go look at a couple of
investment/casting tables, or see if you can find vids on You-Tube
so you can see how people use them, and what they do, before you go
trying to frankenstein one out of whole cloth.
Regards,
Brian.