Casting ?

[frankonthetis]

Have done 3 casting efforts without using a pressure pot. Using Eli-Chem Total Cast Epoxy Resin, silicone 4 slot mold and stabilized blanks using cactus juice. Okay ish results, few noticeable bubbles but some blanks had voids which the epoxy failed to fill.
Reading various articles about casting with a pressure pot it seems this process just gets you bubble free blanks. Failed to find definitive statements saying a pressure pot would 100% fill these voids when pressure is released. Stabilizing blanks when the pressure is released the juice fills all areas that had air.
Does the same concept hold true when you release pressure in the pressure pot or does this process just eliminate bubbles?
Thanks.
Frank

 

[1080Wayne]

Pressure will force the epoxy into the crevices , but some air may become trapped in the process . Releasing the pressure before the resin has cured will probably allow some of the air to escape , but I would expect some bubbles remaining in the resin also . I have zero experience with epoxy casting , but I think you will get the best results casting under pressure .

 

[Curly]

The pressurization air keeps the dissolved air in solution in the resin until it is cured. If you release the pressure before the resin is cured bubbles can come out of solution or if on the surface of the wood, get bigger. Think a scuba diver getting the bends. Leave the pressure on until the resin is cured.

 

[JohnU]

Voids and crevices are always a challenge but…. Pressure will help as long as you get the resin poured in a thin enough state to fill the voids.
Pressure will compress the air to a no visible size. You dont want to release it until the resin is cured. The reason a vacuum is released during stabilizing is it pulls the air out and allows the resin to replace it as pressure equalizes. It's a longer process and can take days since the resin doesn't cure until heated, unlike resin casting. I use pressure even when it's not required just to better my chances of a successful cast.

 

[jttheclockman]

As mentioned pressure just shrinks the air bubble to the point of not seeing. Need to leave pressure on till resin cures. With epoxy resins that is alot longer than poly resins. Now epoxy resin is usually water thin. Not familar with what you are using. Epoxy resin is very good for getting into all nooks and crannies because it is so thin. If that is a true epoxy casting resin you are using. Much different than tabletop resins so be aware of this.

 

[Kenny Durrant]

I agree with everyone that has replied. Not that I'm the one that has the golden stamp of approval. Ha Ha. Just to add that, IMHO, when they say no pressure is needed that doesn't necessarily mean that it the best. I've had some decent cast without pressure but when I started always using pressure the blanks are much clearer. I think it's a matter of getting by or the best possible.

 

[frankonthetis]

Thanks all for your help and suggestions. Figured would have to eventually go the pressure pot route. The arbutus [madrone] burl blanks have some funky voids large and small. Watching some videos they said to pour some resin into the mold first, then place the blank on top then pour the rest over the blanks. The larger voids present no issues at being filled it was some of the small ones that had no resin in them. Unfortunately there was no direct route between large and small voids so hoped the magic of pressure would somehow get the resin into those areas. Sounds like small internal voids will always present a problem getting filled unless you have a direct path for the resin to flow into? Thanks again for your responses, a new learning curve that so far has been enjoyable.

 

[Kenny Durrant]

Another thought is that when I cast worthless wood or whichever name you prefer, how are you holding the wood in the mold? I use museum gel to do so. I put a few BB size balls on the bottom. It does a great job holding it down so it doesn't float. It also gives a small space for the resin to flow under the blank. That might help you. I don't use Epoxy resin I use the Alumilite Clear Slow. With that type resin I found that I'm better off not worrying about bubbles but get it in the pot as soon as possible and let the pressure do it's job. With the extra time you have with Epoxy that might not be an issue. Just a thought.

 

[frankonthetis]

The first effort the blanks stayed in place without and restraint. The next two used nylon strapping across the mold with a heavy old faceplate for weight. The blanks all had small grooves where the strapping touched but were turned off so no problem. My 4 position mold is 7/8" x 7/8" x 5 1/4". The open mold is 6" x 5 1/4" x 1". Originally trimmed the blanks slighter smaller than the molds to allow resin to flow around but have now make them 7/8" square x 5" as most voids are on the top or bottom rather than the sides. Are you using home made molds or purchased ones? Have never heard of museum gel.