By far the most informative on the subject. Turns out I've been making my bags wrong all this time. http://www.joewoodworker.com/veneering/makingbags2.htm You stick a hinge to the bag edges, don't simply stick them together. Look at the animated graphics.
Lastly - a recommendation. I've been using a venturi vac pump for a few years now hooked up to my compressor. Use it for running hold down on my CNC machine and use it for pulling down bags. It works fine for a couple of hours at a time. The compressor cycles a bit, but not too much at the flow rates I use. A lot of suck for a few $$. The site has a nice description of how to build a venturi press: http://www.joewoodworker.com/veneering/v2-about.htm
I've built vac bags with 2 sheets of vinyl film, taped at the edges with double sided sealing tape. Then to seal all the leaks I glue the perimeter with silicone caulk and pull vacuum. The negative pressure inside the bag pulls the caulk into all the tiny holes and voila! 100% sealed.
I bought a roll of continuos plastic tube for around $50 and its lasted years…only just getting near the end of the roll…I sometimes get 1/2 dozen jobs out of a bag …mostly free-bagging .
Nice tip, thanks. I've just folded a wide sheet over and used mastic tape along the 3 edges. Works well first time, but does not like being folded and put away.
I've cut a rocker bed from EPS, about 3" thick at lowest point. Any suggestions for whether/how thick ply I shuld attach to the underside to keep it rigid for putting it in the bag with the board?