Vacuum pots are usually used with Cactus Juice as a stabilizer. After the piece is completely covered in Cactus Juice, the vacuum pulls all the air out of the wood (can take hours or days) and then the vacuum is released and the piece is left to soak in the Cactus Juice for twice as long as it was under vacuum. While soaking, the cactus juice flows into the spaces emptied of air by the vacuum. The key things to take away from this process is the amount of time required for the complete process - the sucking of the air out and then the soaking to allow the Cactus Juice to get back in. The Cactus Juice remains in a liquid state throughout. Most resins will not stay liquid long enough for the amount of time required so they will gel or harden before they have a chance to get into the cracks. If you did find a resin that stayed liquid long enough, it could take weeks before hardening.
When using vacuums with resin, the vacuum is usually used with a fairly slow setting resin, and then only to degas the resin (under vacuum for only a minute or two) before pouring. If you are using a fairly quick setting resin, this degas process could just give you a container of foam as the bubbles expand and then the resin sets.
Using pressure with resin compresses the bubbles in the resin to they are too small to see. They are still there but the resin hardens around them. Take a jeweler's loupe and look, and they are there. Using pressure with resin will force the resin into the cracks the same way, as the pressure will compress that air at the end of the crack, but there has to be a clear path for the resin to get into the crack. It will not pass through wood to find and get into any internal cracks that may exist.
The only way I've found to get resin into cracks I can see is to either:
1). Build a mold around the piece, cover the piece with a fairly slow setting resin, and then put it in a pressure pot around 55 or 60 lbs pressure (40 lbs just isn't enough), and keep it at that pressure until the resin has fully set. This can take a lot of resin and can get expensive really quick.
2). Use a slow setting resin. I have used West Systems successfully but there are lot of others out there. Build a dam around the crack and anywhere you think the resin can escape from (it's amazing how that stuff can leak out and make a mess!). Hot melt glue works well for this, or caulk. Resin seems to almost always find a hole if you just use tape. Pour the resin into the crack, and then leave it alone for 2-3 days, maybe even longer depending on size of crack, temperature, humidity, phase of the moon, any black cats in the area, etc. Once it finally cures the larger cracks (complete flow through from one end to the other) and voids should be completely filled, the smaller cracks may be completely filled, the tiniest may still have voids at the end.
As for fixing your HF pot, you may be able to get a new seal from the manufacturer or check the web sites of other makers of pots. Some of them sell replacement seals and you could get lucky and find a seal the right size. Before doing this however, try a layer of petroleum jelly all around the seal (top and bottom), and then make sure you are not creating a leak by tightening the pot too tight. I know that sounds counter intuitive, but if you really cinch down on the hold downs as hard as you can, you could be warping the lid and creating a crack where you will loose pressure. You want the hold downs tight enough to stop leaks, but not so tight you're warping the lid. A tricky balancing act. The pressure pots you purchase that are actually made as casting pressure pots have lot thicker and thus stronger lids than the paint pots from HF that may people modify to do casting and save a bit of money. I've turned the regulator on my compressor down to 60lbs, and then just leave it hooked up to the pot. It may cycle on and off every hour or so, but it kept the pressure up to where it needed to be.
Needless to say, you could end up spending a lot of time and money on resin before you find a fool-proof method that works for you. I found the above worked for me, but I didn't feel it was worth the effort. That's why I pretty well do segmented pieces now. I know I'm working with good stable materials and know what I'll get in the end.
Hope the above helps. Good luck.
