Why you need a pressure pot AND a vacuum chamber for casting.
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- Опубликовано: 3 авг 2023
- A quick demonstration of why I think you need both a pressure pot and a vacuum chamber for casting parts. Results may differ with thinner casting resins like urethane, but for this relatively thick epoxy a pressure pot is essential. You need the pressure pot for the resin and a vacuum chamber for the silicone.
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#casting
#resin 
Хобби
At last, someone with common sense and experience saying you need both.
In the days before I had a pressure casting pot, I used to heat my epoxy in a shallow container first and run a gas torch over the top twice for all the bubbles that surfaced. It did a great job, but no substitute for a pressure chamber. I sell casts of my sculptures, so bubble free is a must.
Sadly, it's not common sense, or experience, just learning the hard way 🤣 Thought I'd pass it on to save others from the same fate! Cheers!
you do not need a vacuum chamber to get bubbles out of silicone. just set the form on the floor, then slowly pour silicon from a container held about chest level. this creates a very thin stream of silicon and automatically removes most of the bubbles
Well i use pressure pot for silicon molds and it works good enaugh. I dont have vacuum chamber and no lambs in my casting.
A small RUclips channel called Jenner custom toys makes pressure pots out of cheap 3 gallon buckets and a Tire valve. He says he gets pretty good results with just like 10 or 12 lb of pressure using an everyday bike pump. I'm really surprised it hasn't caught on.
I've seen that video. I think it depends on the viscosity of your casting resin. I use a pretty thick epoxy and if I set the pressure pot to much less than 60 psi I will get some small bubbles.
@@RichardThompsonCA Ahh! That makes sense. That's actually really useful because I may be doing some light resin stuff soon and I can intentionally stick to thin resin and skip the heavier setup. THANKS!
@@VagabondTE It's the same with silicone too, you don't need a vacuum chamber if it's thin enough. Smooth-On (and other manufacturers as well I'm sure) makes a silicone they call NV29 (NV stands for No Vacuum) and it's much thinnner than their other silicones. I prefer the thicker resins as the molds I make are designed for injection. I use a large 250 ml syringe. I find the water-thin stuff trickier to get in without splashing and spilling if you have to pour it, and it's too thin to be used with a large mouth syringe, it just pours out. Cheers!
@@RichardThompsonCA Unfortunately thin silicone doesn't really work for my purposes. I recycle HDPE plastic in toaster ovens using a spring-loaded all metal press. It has quite a bit pressing pressure. Fondant molds, acrylic clay molds, and bakeing supply are the only silicone I can get extended-use from. I'm not even sure if you get that kind of strength from any two-part silicone. Or at least I don't know which one.
Sorry, but let me be clear, the reason he has bubbles in the vacuum chamber is his own ignorance. When using epoxy resin for vacuum you degas the Epoxy Resin before you pour! But can you use it during molding? Yes! The 2nd mistake he made was that he used way too thick epoxy resin for his project (Clearly states it in the video) or did he even have the right epoxy resin and he didn't check to see if there were any conflicts with the material. Yep, that's right, the mold you use can be a cause for bubbles!
This is a biased video. Pressure pots are nice and there uses for everything. I have both, but I don't use both all the time. In fact, it's rare that I use a pressure for what he does. I normally only use it on small things. But using both is time consuming, so use them wisely.
There is an infinite amount of times people claim it was the vacuum and it was their mistake. Like I said, everything has its uses.
Note: There are many videos that explain the US of both Vacuum and Pressure Pot in the Dice making videos .
so biased.. do not forget using heat too
Does it make a difference to use just pressure pot vs first degassing the resin and then using the pressure pot?
Reason I'm asking is some of the poly resins have about 6-7minutes of pot life, so there might not be enough time to do both
From my own experience, it's not really beneficial to degass the resin first if you have a pressure pot. I tried with and without, and the results were the same (no bubbles). I also found that if time only allowed me to one (vacuum OR pressure pot) I got the best results with pressure. I think vacuum is only necessary for the mold silicone.
@@RichardThompsonCA Thank you for the response. I just got a pressure pot and i was able to test it myself. Did some tests with only vac, both and only pressure.
Only pressure and both resulted in the same end result which is no bubbles at all.
I usually cast very detailed parts so i have to make 2 part molds and if i skip a vent hole i will get a chunky bubble %100. The one tried with has about 20 vent holes on it and i made this interesting test with it.
I plugged about 15 of the vent holes so there was no venting where the resin will be trapped. I only left the vents which are vertically at the top most surface as in pour from low spot and rise to the top. Basically I allowed the resin to rise naturally but i did not let it find its way to the details in mold.
It was incredible to see the result, I was expecting some bubbles here and there for sure but it came out absolutely bubble free!
So the way i see it, pressure pot is actually beginner friendly and allows you to make logical mistakes while making your mold. For me it will just allow me to put less vent holes :)
Anyway man thanks for the input.
@@orhanyor Glad it's working out for you! One thing I need to point out, in my tests there was a limit as to the size of bubble you can crush with a pressure pot. If it's really big it will get smaller but still be visible. So it won't cure problems like outright voids in the casting.
@RichardThompsonCA yea definitely, the ones that I'm talking about are probably 3-4mm in diameter. I don't think it will fill a hazelnut size void :)
The places that I'm struggling with are the sharp edges and thin sections like 1mm thin walls. Even with vent holes bubbles can sit on the sharp edge because of the surface tension or just because bubble is basically bigger than the vent hole etc.
Well, all of it is gone. I even checked it under the microscope see if I can see the crushed bubbles but somehow they are smaller than the microscope can magnify. BTW I used 60 PSI for every test but my last test was with 40 PSI just to see if it makes any difference but result was the same.
@@orhanyor Yeah, I found 60 psi works well. While some like to go higher, my pot is only rated to 80 and I don't feel like pushing my luck. I did try one at 20 and there were some bubbles.
Which one are you supposed to use first?
You use the vacuum chamber first to degass the silicone to make the mold. You only need to do that once, when making the mold. Then, when casting, you use the pressure pot to remove bubbles from the resin, for every casting you make.
@@RichardThompsonCA So you need both because neither vacuum nor pressure will work on both silicone and resin? 😲
@@DEarls-ye9tz Correct. Vacuuming resin doesn't seem to make any difference to the outcome, at least in my experiments, only a pressure pot will get rid of the bubbles. But using a pressure pot on silicone is not advisable. If the mold master you are making the mold around is hollow, the pressure pot will cause it to deform/crush , ruining your mold. Also, when you crush the bubbles in silicone, then remove it from the pressure pot, they will just expand to their original size, due to the softness of the silicone. Those expanded bubbles will displace the silicone around it making it lumpy on it's surface. Crushed bubbles in resin can't expand again once the resin hardens. Two different devices for two different materials.
@RichardThompsonCA Thank you, you've helped me understand all of this much better. 😄
Trypophobia
How? How can anyone be afraid of holes.