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RTV casting tools...looking for advice

5355 Views 16 Replies 7 Participants Last post by  rkapuaala
I'm looking for recommendations regarding what I should be looking for to develop a casting capability using RTV molds. I have the mold master...so I'll need to be able to make the mold and then make the parts with the mold. I'm not interested in what materials to use...yet. I know RTV comes in a variety of "qualities". But this request is about the tools needed.

I think I need three "tools":

a. Paint pot, in which to do the mold making or part making

b. Vacuum pump
[*]to pull air out of the RTV when making the mold from RTV and [*]When using the finished mold, to pull air out of the resin after it's poured/forced into the mold [/list] c. Presure pump to force the resin into the RTV mold

Is this correct? If so, then what are the specs I'm looking for?
[*]How many inches of vacuum dose the vacuum pump need to pull? [*]How much capacity does the vacuum pump need?...How fast does it need to pull the air out of the paint pot....10 seconds...or 10 minutes? [*]Same for the pressure pump....how much pressure does it have to put out....how fast does it need to pressurize the paint pot? [*]I've found paint pots up to 2.5 gal in size. What size is used by most modelers? Where does one find one in larger sizes...say 5 gal? [*]What gauges are needed on the paint pot to measure vacuum or pressure. What kind of valves? Where does one get the valves. [/list] I'd LOVE to see a photo or drawing on how one of these things is set up. Does anyone have one?

Lastly...some questions related to size. If I wanted to cast a 3' long passenger car side, how does one size this stuff up? What kind of paint pot would work and how much bigger do the pumps need to be.
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I have some boxcar sides I cast that are about 24" long, so 3 feet is probably possible. These are ambient castings though, not pressure castings. The trick is to make the pattern with shallow detail. And when you pour it, be quick! Any air bubbles on the back get filled with CA & sanded down smooth on the belt sander.


The best advice I can give you right now is: start small & work your way up. Trying a 3' casting right off the bat would probably have frustrated me to the point of giving up.
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Sorry for getting off on a tangent...

Personally, I have a 2.5 gallon Sears paint pot that I use for pressure casting. I made my own vacuum chamber from a 6" PVC coupling and lexan (never use Plexiglas). It uses a small vacuum pump that I got off eBay - I think it's a Gast pump - and it only draws about 25-26" vacuum. If I had it to do over, I'd get a bigger vacuum pump, and make a bigger vacuum chamber.

I only degas my RTV long enough for it to rise & fall. Then I'm careful to pour with a long, thin stream and that seems to get all the bubbles.
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