Pressure pot and casting: Need help!

[JMC]

Hi,

does anyone have any advice or tips for casting or mold making with a pressure pot? I hate these bubbles and especially with smaller objects.

Any help would be appreciated.

[johnmiic]

We used to have a guy on the boards who worked with that technology but I don't think he's around here anymore. Sorry.

[LonnieFisher]

I have a pressure pot and it works great to make the bubbles go away!! Too bad I can't use it right now. My hands are trashed and need some more fixing...
My advice...
use resin that has a seven minute work time. It'll take longer to set and de-mold, but it's worth it for a better casting. Use slow cure silicone to make the mold. Cheap silicone sucks. Use expensive silicone. I use silicone with an eight to ten shore. De-gas your silicone before you make the mold.

[JMC]

I have a pressure pot and it works great to make the bubbles go away!! Too bad I can't use it right now. My hands are trashed and need some more fixing...
My advice...
use resin that has a seven minute work time. It'll take longer to set and de-mold, but it's worth it for a better casting. Use slow cure silicone to make the mold. Cheap silicone sucks. Use expensive silicone. I use silicone with an eight to ten shore. De-gas your silicone before you make the mold.

When you say de-gas is that with the pressure pot? Besides the pot, what else do I need?

[gaga4toyz]

if you don't de-gas the silcone before you make the molds you have little zits all over your parts where the plastic is forced into tiny air pockets in your mold. You need to buy a vacuum pump and a vacuum chamber to de-gas the silicone. Vacuum pumps are expensive for good ones. I've heard of people using vacuum cleaners and stuff, but I don't know about that. I think my pump was about $300 on ebay. There's probably cheaper ways to do this, but I wanted something that would hold up to lots and lots of castings.

The easiest way to do this is to make your molds under 45 psi in your pressure tank. I take a piece of plexiglass (or lexan) bought at home depot and superglue my head to it (neck down) Then I take a pvc plumbing fitting and glue it down to the plexiglass (the head will now be sitting upright inside the pvc fitting) Mix up your silcone and pour into the pvc fitting slowly. After the pvc fitting is filled, close the top of the pressure pot, adjust pressure to 45 psi and leave the mold under pressure until it's completely set. I've made 1000's of perfect castings from molds I've made this way over the last 10 years. Some people will tell you that you have to degas the silicone and that isn't true.

If you PM me I can give you my number and walk you thru the process. I can also send you pics of how it's done.

[Tothiro]

^ Yeah, pressure casting and degassing are two sides of the same center result... If you make the mold under pressure it will work just as well as if you'd degassed it for the most part.
Vacuum chambers can be done fairly cheaply though - you just need a pump, a paint chamber from a nautical supply, some thick lexan and a few fittings/release valves. The complicated bit is modding some threads for connections, but it can mostly be done for about $120 to $150... compare that to off the shelf kits which will run between $300 and $400.
Pressure pots on the other hand you want to be seriously careful about because the potential for dangerous disaster is much higher. I wouldn't suggest any handyman specials there because you're much more likely to end up with insta-projectile shrapnel.

I am a giant hypocrite because I'm running with neither right now...