Re: Investing and Bubbles


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Posted by Jack Davis on March 15, 1999 at 20:42:08:

In Reply to: Investing and Bubbles posted by Dan Caster on March 14, 1999 at 19:55:41:

You could spatter a thin plaster on the model with a brush or plaster gun as Bruce spoke of, but I would probably be designing an economical bell jar or like housing for vacuuming the investment. For anyone casting Breadbox down sized investments, vacuum chambers are not a must, but are certainly practical. Though I haven't made one, image a sealed drum upside down on a flat rubber base with a suck hole in anywhere in it. Come to think of it you might be able to put your investment in a heavy plastic bag with a controled inner shape (say a 3 gallon flask and a hardened top and bottom so that the bag couldn't collapse and suck the plaster out the vacuum source hole..... I know this must sound a little confusing, but imagine the plastic bag as a form fitting bell jar with the base self-inclusive. The main goal is to keep the bag from collapsing into the investment plaster, by topping the flask with maybe a perferated flat lid. You would probably need to double the bag for strength. Stick a shop vac in the bag opening and rubber band tight. I just made this crap up, but I would be willing to bet that it will work....My thought is that this might work as well for larger castings that you can't get into the average bell jar, or would be very simple on a small item like a one pound coffee can size....Even if this should become state of the art, which I'm sure it won't, I would look for a more regulatable vacuum source (rather than the shop vac), so that you can better regulate the system......Jack Davis

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