So I have two vevor vacuum casting machines both with the same problem … they work, when I use the vacuum chamber to the right with a solid flask on top, I get a seal an it pours right, but I just can’t get a seal on the bell side with both of them…. When I cover the wholes with my fingers the gage shoot straight up so I’m getting the suction, I’ve tried oiling the pad , even taping the pad down on all sides, and I still get nothing, the investment never bubbles… can anybody help me? I’ve literally ordered 6 machines now with the same problem an sent two back to Amazon 
Can you post an image or two of your set-up? That would be helpful. I know folks who put vaseline on the bottom of the bell jar to create a stronger seal, but I’m not sure if that would help you. Let’s look at pictures of your set up and we’ll see what we can figure out.
A jewelry tool company told me once that if you put a pint of water in the vacuum chamber, then turn on the vacuum chamber that it should “boil” within 1 minute or so. That’s a pretty easy test to do.
Hopefully it’s something simple!
Jeff
Have you also tried water or vaseline between the rubber mat and the metal platform and is the platform completely clean and free of any investment powder? Is your rubber mat in good condition? When they get old and stiff they sometimes fail to make a good seal to the platform as well as the bell jar. Hope this helps.
Have you checked the valve that switches the vacuum from the casting side to the bell jar side? It would be really weird for two machines to have faulty valve switches, but you might want to double check.
Donna
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Dm me and I’ll FaceTime you if you like.
I looked up the machine you are using. It is set up to cast perforated flasks and to do investing. Many years ago , when I used a similar machine, I had to sand the bottom of the bell jar perfectly flat . It is a small belljar, so you need to find sandpaper wide enough so you can easily sand it flat.
If that does not fully solve the problem, The flat table might not be perfectly flat… that can be a problem . You can check that by putting the edge of a ruler across the platform… if there is a gap, that may be the culprit! You may be able to find a softer silicone seal which could help.
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