There's not much to it, it's just an airtight frame with a sheet of something airtight glued or screwed to the top, a fitting in the side to suck air out through, and a gasket on the bottom so it seals against your table. Results may vary depending on what you make your frame, gasket, and membrane out of. The best home-makeable systems use a neoprene or silicone rubber membrane and a neoprene closed-cell foam bottom gasket with a plastic or aluminum frame. You can make it work with a plywood frame, a piece of garbage bag, and a length of O-ring or weather-stripping (if you're handy enough...I don't recommend this route unless you have waaaay more time and skill than money
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