Pressure pot V Vacuum pots for casting

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I'll add to what David said.

A Pressure Pot uses pressure at 2-4 times the normal atmospheric pressure to compress bubbles in your resin so the bubbles cannot be seen when the resin is cured.
A Vacuum Chamber uses suction to pull the air out of the chamber which also pulls the air out of what is in the chamber (resin, silicone, wood, etc.).

I hope this helps a little.
 
Vacuum is used for casting. Some people use it to degass their resin before mixing.
It can be used to remove air in the resin, but you need a very long open time. The vaccum will cause the resin to foam, as the air moves out of the resin. If this is done rapidly, it will be a huge mess. The same happens when stabilizing, but in stabilizing you have the time to slowly increase the vacuum, thus controlling the foaming action. Think hours vs minutes.
 
darrin1200 said:
Vacuum is used for casting. Some people use it to degass their resin before mixing.
It can be used to remove air in the resin, but you need a very long open time. The vaccum will cause the resin to foam, as the air moves out of the resin. If this is done rapidly, it will be a huge mess. The same happens when stabilizing, but in stabilizing you have the time to slowly increase the vacuum, thus controlling the foaming action. Think hours vs minutes.
Click to expand...
I think this needs a bit more clarification. Casting is done under pressure, but as Darrin says, some people use the vacuum early in the process to degas their resin (like me), but the actual casting process/cure is done under pressure like @d_bondi and @NeonWoodShop stated.

When degassing my resin, I use the vacuum tank for less than 2 minutes to just pull excess air out of the resin prior to pouring it into the molds. This is done in the mixing cups, not the molds. I do it early in the time cycle of the cure, typically right after the initial mix of the 2 components (I use Alumilite Clear Slow typically). My goal is to get the most amount of large air collections out of the resin introduced by the initial mixing process. It is impossible to remove it all, so once everything is in the mold (I do vertical pours), I put it under pressure. It foes foam a bit, but it is manageable and proof that air is being removed.

When I do flat, rectangular pours, I do not do the vacuum step, as the depth of resin is way less than in the 9" vertical molds I use. I believe the air pockets left in a shallow rectangular pour are easily handled through the pressure cycle, but with the vertical pour, once the resin starts to thicken, I think the chances of air remaining in the molds is greater, causing air pockets in the resin, so I like the added caution of the first vacuum step. Some folks think the vacuum step is not required and just adds more work to the process. I don't really have any good proof that they are incorrect, as my pours have usually been solid without bubbles, but I have the time and the equipment, so I consider it extra insurance. Using caution to introduce the least amount of air into your mixing process is also a smart move, no matter what depths you pour at.

Hope this helps.

Kevin
 
In simple terms....

Vacuum chamber: sucks air out of whatever is inside; for stabilizing it pulls the air out of the wood and allows the stabilizing liquid to seep in so it can be hardened - can put epoxy in vacuum to suck out bubbles before pouring but be careful to not let it bubble over just as hardening fluid

Pressure pot: put pressure on whatever resin is inside of the pot; basically crushes air bubbles to make them so tiny they don't create voids and you end up with clean casts - can also cause resins to seep into voids in the wood causing the resin level to go down
 
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