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Casting/Investment Table


I’m thinking of building a Casting/Investment table which I will use
primarily for removing bubbles from investment. I can purchase a 30
PSI Thomas Industries air compressor and vacuum pump which operates
on 115 VAC, 60HZ drawing 3.9 amps. The pump provides 20 - 30 PSI and
pulling 20 in-Hg air pressure. It can operate either as a vacuum
pump or compressor depending upon whether treat the pump intake or
exhaust as “output” and hook it to a chamber/tank. This is a single
stage pump. Question: is this pump sufficient to make a proper
Casting/Investment Table?


The answer is no. You need a vacuum pump that will pull at least 29
inches or better, and one that will pull it quickly. Your investment
will not break until you reach the 29 inch pull. The higher you are
above sea level, the more oomph you need. A pump rated at 25 micron
and 3cfm is the least you need.

Dayton makes a refrigeration service vacuum pump which is what a lot
of the commercial vacuum units use. It is reasonably priced as
vacuum pumps go. The last one that I purchased for repairing a
customers machine cost around $310. That was about three years ago
though. I expect they have gone up in price somewhat. A "good"
vacuum pump can cost you well over a thousand and some run up to the
two thousand range. Check with Graingers as one source. Mcmaster
is another source.



Hi, This pump / compressor is not adequate for casting /Investing. You
first need to know the cubic footage of the bell jar. then from this
you can calculate the size pump neccessary to do the job. You should
be able to pull down to 29 " mercury in Under a minute…

This is absolutely neccessary if at any time you get into “stone in
place” casting and the investing proceedure is no longer "normal ".The
speed that you can get the investing done in is critical. Our pumps
can hit full vacuum in about 10 seconds. We use a 28 cfm bush pump (
not cheap). If you use a small bell jar , that will only accomodate 1
large flask or a few smaller flasks, then a smaller pump can be used.

The small Inexpensive pumps that are rated to 29 " mercury usually
break down in a short period of time as particles of investment get by
the filter and water that evaporates in the bell jar is sucked into
the pump it self. Frequent oil changes will extend the life of small
pumps. Oilless pumps ( which do exist) will not work. There are small
pumps that will work perfectly, but they are not the cheapest animals
on the planet.Your investing tabletop should be mounted on 4 springs
so that your table can be jiggled to help remove pesky bubbles.

You can use car oil filters with an external (car) oil filter adapter
available at most car parts stores ( $15 for the adapter) and your
filters will cost you about $ 3 to $ 4 to replace when they become
useless.This is the least expensive filter system and should be placed
before the valves and gauges coming from your investing and your
casting platform.This is so that your gauge, valves and pump will
last a long time As far as plumbing / piping size, the bigger , the
better… use piping that is equivalent to the pump input hole. make
sure all fittings are taped with tefflon tape and are tightly screwed

Coming from the casting chamber and the investing table , use heavy
duty rubber hose with a steel coiled wire insert on the interior so
that the hose will not collapse.Make sure all clamped connections are
tight. This hose will allow your investing table to be Jiggled by
hand or with an automatic vibratory attachment that is firmly
anchored to the underside of the investing table. The hose is
connected to a fitting on the car filter adapter. From the car filter
adapter to the valves and pump You should use copper or galvanized
steel pipe to reduce the effect of rust on the interior of the pipe
due to evaporated water.

Use the same type of hose from your casting platform to another car
filter. This will allow you to remove the casting platform by simply
loosening a single hose clamp from your casting trap.This will also
isolate your casting platform from vibrations from the pump.

Use a 3 way or 4 way valve after the car filters, so that you can
direct the vacuum to the table you wish to use. It is not neccessary
to built a storage tank or an insert style tank for the flasks. A flat
platform can be used for casting and can be seen at my website .

Under the platform, with simple galvanized fittings, you can build a
simple trap to collect any metals incase you have a blow out.This
trap is piped directly Into the flat plate of your casting table and
is the vacuum source for casting. Under the platform should be a T
shaped fitting. 1 part of T goes the top plate, the other side of the
T goes to your casting trap, the third part of the T is where you
attach the hose going to the Filters.Hose/pipe size is not critical
coming from the casting table to the filter.

If you have any questions, You may call me between 9: 30 am to 5:30
pm eastern standard time and I can answer your questions.Tel:
401-461-7803 Daniel

We do casting, finishing in gold, silver, bronze/brass and pewter for
people in the trade

I'm thinking of building a Casting/Investment table which I will
use primarily for removing bubbles from investment. 

I never tried this but was told to go to a junk yard and buy the
compressor from an air conditioner off an old car. This would pull
the vacuum needed for casting. Then use an electric motor to run it.
Just a thought.

John Daly
Grand Junction, CO.


I made my own vacuum set up. I took the compressor from a small
suitcase sized window Air Conditioner, used reinforced 3/8" hose from
my local hardware store and an automotive vacuum gauge and a valve to
release the vacuum, teed into the line. I pull 27.5 to 28" hg, I use
this both to invest and so far up to 1.5 oz T. of silver for casting.
I made my own 'vacuum chamber from a 8" PVC drain line connector and
found a “Visions” glass pan lid as a see through lid to watch the
debubbling. Plate glass will NOT work, the pan lid is a tempered high
heat domed glass and works well (1.5 years ~~75 pounds of
investment?), I joined/sealed the lid and pvc pipe with automotive
RTV Form-a-gasket, and glued a rubber sheet to piece of particle
board as a base, a smear of petroleum jelly helps this seal quickly.
My vacuum line is screwed into the pvc pipe mid way up the height to
avoid over flow problems. To vacuum cast I used a scrap piece of 8" x
2" steel channel beam with a ell connector through the middle, so far
I use wet cork material as a casting seal, wet paper towel/newspaper
also barely serves . I’m using a propane/MAPP torches to cast and
burnout with. My burn out kiln is a 4 fire brick base with an
Terra-Cotta 8" Azalea flower pot, (crude fast and effective – cheap
of course!) Poverty creates ingenuity. (I’m currently a middle aged
College art-metals student, with a family.) Enjoy!

I didn’t fight my way to the top of the food chain to be a vegetarian.


Using glass of any kind as a part of a vacuum system with out safety
shields around it is extremely dangerous. I know that it has been
done for years in laboratories but now days if you see a glass bell
jar in a lab there will be a steel mesh safety shield around it. If
the glass is even lightly scratched it can implode when put under the
stress of 14 lbs per square inch. Your 8" diameter glass lid has
more than 700 pounds of pressure on it! (area of an 8" circle is
50.26 square inches times atmospheric pressure of 14 pounds per
square inch = 703.71 pounds of pressure on that lid) The continual
cycling of pressure can cause a small scratch in the glass to
propagate and eventually fail catastrophically throwing glass shards
all over the room. If you want to make your own bell jars do it in
thick acrylic not glass. If the plastic fails in a much less
dangerous fashion.

Jim –

James Binnion Metal Arts