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Vaccuum for investment

I hope the casters out there can help me. I’m a year into working
with metals and I can’t get enough of learning about the different
techniques. Not to long ago I got a great deal on a centrifugal
caster and a burnout oven. My readings led me to believe that to get
a good casting one needed a vibrating table or better yet a vacuum to
get the air out of the investment. Somehow I came up with a vacuum
from a lab that I hoped would fit the bill. I made a bell jar and a
plate which would hold a good vacuum and I was off. The problem is
two fold. First I am at 6500 feet so I have been told that I should
expect less of a vacuum than I would if I were at sea level. I can
get about 22 ?? on the gauge of the vacuum. This will not boil water
as many of the books suggest as a test for the efficiency of the
vacuum. When I de-air the investment I get some bubbles but not the
1/4 inch rise in the investment level that again the books suggest.
Can anyone tell me if the vacuum I’m getting is still helping or if I
need to find another source for a vacuum.

This leads me to a second question. A friend and teacher uses system
that attaches to the sink and creates a very good vacuum. Harbor
Freight has a vacuum that uses air (which I have a source of) instead
of water to evacuate freon from air-conditioning, does anyone have
experience using this product and can it work as well as water. I
don’t have a lot of water pressure near my shop.

The books some very old suggest “green soap and alcohol” as a
debubbler. I have had no luck finding a source for green soap. A
pharmacy said they could order it but in a quantity larger than I
need. Any suggestions.

I hope the same people who have given me the good advice in the past
can come through again.


Darling by Design
Doug Darling

Green soap was used in my ceramic/pottery classes when making plaster
molds…maybe a ceramic supply house? Donna in VA The books some very
old suggest “green soap and alcohol” as a debubbler. I have had no
luck finding a source for green soap.

Hi Doug, Raise Your water Temperature up to 90 o F and your investment
should boil fine… Watch your setup time as It should freeze up
faster…Mix a trial 2 lbs batch and time it. if you want to extend
the time slightly, add a little more hot water And test it again. Your
investment should setup at about the 10 minute mark. Daniel Grandi
casting and finishing in gold, silver , Brass/bronze for people in
the trade.

Doug try adding about 1% of citric acid to the water and raise your
water temp to 100 degrees F . The citric acid will slow down the
setup time of the investment to compensate for the higher temp. and
the higher temp will allow it to boil at the altitude you are at.

James Binnion Metal Arts

Member of the Better Business Bureau

Doug, Iam in Colorado and at about 5700 ft maybe.Just east of the
foothills and I not only use a vacuum to debubble my investment I cast
with it too.I never get over 22 either.After I invest I use a small
vibrator to further the debubbling.I would stay away from soap or
debubblizers.They can contaminate your investments.I have never used
them.My bell jar sits on a rubber pad and I wet the pad where the bell
jar sits prior to setting the bell jar on the pad this helps me see if
I have a good seal.You said you made a bell jar.Do you have a good
seal?I would invest in a good jar .They aren’t that expensive.Also
does your pump use oil and have you checked all the connections
filters and seals on the unit. Regards J Morley Coyote Ridge Studio
Where spring has sprung and the asparagus has too. mmm!

You might think about using pressure to get the air bubbles into
solution if the vacuum doesn’t pan out. You don’t need great
pressure, 10-15 lbs. Might be easier to do this at you heights.

John Dach

Hi James; do you still believe vitamin C will slow down investment set time? IF so do you still believe in 1%? Using ice water does not prolong set time enough for some of my castings. Large flasks to be cast with bronze take a long time to mix and pour… I would love to have 20 minutes of working time if at all possible.