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Vacuum casting table using a recycled parts

Jewelry Discussion
#1

I am interested in any discussion about homemade tools. I am
begining to get into the hobby of silver casting and the idea of
spending a lot of money on tools is a little discouraging. I have
kept an eye out for inexpensive used tools in my area but they are
hard to find.

I would like to build a vacuum casting table using a recycled vacuum
pump I’ve acquired. The pump is a little larger than the standard
vacuum pumps I’ve read about in the specs on casting machines in the
cataloges. The pump I have is a Robinair high vac 10 cfm pump. Will
it be acceptable for use in a homemade vacuum table for investment
prep and casting? The casting machines seem simple enough to build.
Has anyone built one? Any source for plans?

I read an old book mentioned on this list about building your own
burnout ovens and other tools for home use but it may have been in
the pre vacuum casting era. I don’t know. Any suggestions from those
of you who have been down this path before would be appreciated.

Thanks,
Ken

#2

Ken,

A 10 cfm pump is over kill. Change the oil, install a trap and you
are good to go. I use a 3 cfm and am quite happy. Plans I have no
source other than look at catalogs and improvise. Over design the
bell jar, I have never seen vac implosion and don’t want to. An over
sized pump won’t pull a better vac, just faster.

jeffD
Demand Designs
Analog/Digital Modelling & Goldsmithing
gmavt.net/~jdemand

#3

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.

#4 
I would like to build a vacuum casting table using a recycled
vacuum pump I've acquired. The pump is a little larger than the
standard vacuum pumps I've read about in the specs on casting
machines in the cataloges. The pump I have is a Robinair high vac
10 cfm pump. Will it be acceptable for use in a homemade vacuum
table for investment prep and casting?

Yes that will actually be much better than the typical pumps found
in studio scale vacuum casting systems. Pumps are the most expensive
part and the typical place to save money is to use a smaller pump
and take the performance hit. So a 10 CFM pump is a great asset. the
vacuum table can be a simple steel or aluminum plate big enough to
accommodate the bell jar. You want fairly thick plate like 1/4 " or
3/8" for a 12" bell jar. It needs to be flat and smooth so that the
rubber gaskets used to make the seal will be able to do so.

The casting machines seem simple enough to build. Has anyone built
one? Any source for plans?

Yes I have built several, ranging from a simple plate to very
complex systems, none of it is all that difficult. Your biggest
issue after the pump is a good flat smooth plate. The bell jar is
the next item that you will need, I would suggest you buy a good
acrylic one. You can make a vacuum chamber but it will typically
cost more than buying a bell jar.

Such projects usually go better with images so if you want to kick
around some thoughts on how to do this you can contact me off list
and I will send you a sketch of how you can do this.

I read an old book mentioned on this list about building your own
burnout ovens and other tools for home use but it may have been in
the pre vacuum casting era. I don't know. Any suggestions from
those of you who have been down this path before would be
appreciated.

I have built a couple of electric and gas kilns there are books and
info available but I would suggest you do a lot of research before
tackling this as it is a good way to hurt yourself or start a fire
if you do not do everything just right.

Jim

James Binnion
James Binnion Metal Arts

#5

Personally I haven’t, when I use investment I use a "bombs-away"
method to pour my plaster (also works with RTV rubbers), no bubbles.

The downside is that it’s slow, compared to using a vacuum.

A few of my peers on the Yahoo! casting groups have built vacuum
casting apparatus.

Regards Charles A.
P.S. It’s not rocket science :wink:

#6 
I would like to build a vacuum casting table....Has anyone built
one?

I have. It works fine and was not hard to make. Mine has space for a
bell jar on one side and a vacuum chamber next to it. I used 1/4"
aluminum for the top.

The top needs to be quite flat on the side for the bell jar, for
vacuuming investment, RTV, etc. or you will have trouble getting a
seal.

For the vacuum chamber I got a stainless steel pitcher from a
restaurant supply outlet. The pitcher had straight sides and a flared
top. After sawing off the handle it dropped right into a hole I cut
in the aluminum top. You need to drill a hole in the bottom of the
pitcher and rig up plumbing fittings to route a heavy hose to the
vacuum pump. Put a piece of metal screen in the chamber over the
bottom hole.

I got a very large filter from Contenti. It looks like a jumbo
automobile oil filter. That is plumbed between the chamber and the
pump to catch any investment dust.

I cut various size rings out of the 1/4" aluminum sheet and use
gasket material, so I can place larger or smaller rings over the
vacuum chamber to accept larger or smaller flanged flasks. You can
get heat-resistant rubber rings from Rio Grande.

I can provide more details if you contact me off-list, but it is a
pretty simple ‘machine’ and anything you cobble together will work
fine so long as you have a flat top for the bell jar and you make
tight seals on all vacuum connections.

Test your vacuum before you actually cast. Put a flat metal plate
over the chamber hole and sealing ring.

Word of caution. Turn the vacuum pump on after you insert the
flanged flask into the chamber. If you turn the pump on first, when
you put the flask over the chamber hole it will get sucked down with
such force you will never forget it. : )

Neil A.

#7

I built mine ! it is a stack cabinet assembly with vent and hood it
also has a vent from the vaccum table to the hood with the oven over
the vaccum table. The pump is stored underneath in the cabinet and
best of all i found the vaccum gauge in the bottom of a bucket at the
bi anual antique car swap meet at the county fair grounds in
springfield Ohio for the amazing sum of $1 US dollar ! ask Brian
Meek (Alberic) he’s seen it ! - goo