I was out in the shop last night testing what I thought would be a great new vacuum bag design, but things didn’t go as planned. My design used a frame with vacuum bagging material stretched over it, and closed cell foam around the bottom. The frame is then placed on the platten, clamped down, and a vacuum is drawn, eliminating the need to wrestle a large panel into a bag. This is similar to some industrial vacuum veneering systems, but simplified for a home shop.
The problem I have is that I can’t pull much of a vacuum. Obviously this means leaks, however they must be small cause I am having a hard time detecting them. Have any of you built a similar system to this, and if so, could you share your experiences on making the system seal up properly.
I’ve already got a couple of the typical style vacuum bags that I’ve made, but veneering big things worries me, as it’s a hassel to get everything into the bag, and I don’t want to risk some delicate veneer that I will be pressing onto some large cabinet doors.
Thanks
Andrew
Replies
I've never done any vacuum bagging, but I do have 18 years experience in the high-vacuum industry. If I understand you correctly you've made a bag that is half vac bag material, and half closed-cell foam. If this interpretation is correct what you most likely have is a ton of what are known as "virtual leaks". These are small spaces containing air and water that are completely within the vacuum space (that would be the closed-cell foam). On top of that I suspect that the closed-cell foam is not all that air tight.
I was surprised to learn that many CNC Routers (the big computer controlled "cut the project out of a sheet of plywood" machines) hold the wood in place by vacuum.... THROUGH A SHEET OF MDF. So obviously some of the materials that I thought were rather air tight (like MDF) are far from it.
I don't know about closed cell foam, but you might try a layer of vinyl that is known air tight over the foam or other materials.
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Charlie Plesums Austin, Texas
http://www.plesums.com/wood
Andrew, I have done lots of projects that just will not fit the standard bags, and what I usually use is carpet tape and vinyl to build the bag around the work. I keep rope-caulk on hand to stuff into any wrinkles and around where the hose goes in.
The tape I use is 1.5" wide cloth. Don't use the plastic film tape isn't sticky enough, and the fiber-glass type leaks. I usually get 28" Hg without any problem.
I have been getting request to teach another weekend workshop of my methods, which will probably be sometime in Jan - Mar.
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