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Making Your Own Vacuum Bag

Project too big for your vacuum bagger? Make your own bag with plastic sheeting. July 11, 2005

Question
Over the last couple of years I抳e used more and more of my own re-sawn veneer on furniture projects and I like the way you can get a nice consistent or book matched appearance. I have come to appreciate this as a way of using some of the more exotic woods more efficiently. Most of the time, I use a vacuum bag to apply sheets of edge-glued veneer onto the substrate.

I have a job coming up that I would like to use the vacuum-bag process on, but the piece is far larger than my 9 foot bag ?how has everyone solved this problem? Would it be possible to cobble together a one-shot vacuum bag with visquine and duct tape? Could the bag be taped to the substrate itself? Any help would be appreciated.

Forum Responses
(Furniture Making Forum)
From contributor B:
I came upon a situation like yours where I had a piece to glue which was longer then my 8 foot bag. I used a pretty flat bench topped with a 4x10 sheet of 3/4" Mdf. I then tapped the sheet for a vacuum connection. I ripped up strips to elevate the work piece/substrate (positioned over the vacuum tap, this acts like the grooves cut into your board in bag system).

Then I laid up the substrate and veneer, and caulked on the top. I then had some 6mil polysheeting laid over the whole thing and duct-taped to the MDF table. I pulled a vacuum and there it was ?it wasn抰 perfect, but it held 12-13 inches and ran my pump constantly. For the one shot deal it worked great. With a little tweaking and a better membrane or seal, I don抰 see why it wouldn抰 work perfectly. My veneer was very flat to start with and only a 26x112" size.



From contributor K:
I have always made my own bags using vinyl that I buy from a wholesale auto upholstery supply store. It comes on 54" wide rolls, and can be cut to whatever length I need. They sell a contact type adhesive for gluing vinyl.

Whenever I need a one-off bag, I use cloth core carpet tape which is sticky on both sides. I keep rope caulk handy for stuffing a little pinch into any wrinkles, and around where the hose passes through the film.

On really large projects, I find it easier to do the glue-up right on top of the bottom half of the bag, then just peel the tape and stick the top and bottom halves together. I have not had any problem holding 25" Hg. on projects over 20' long. I usually use epoxy for my adhesive for this kind of work because of the longer open time and lubricity for bending.




From the original questioner:
I have come up with a few more questions. Contributor B: Is what you抮e calling ? mil polysheeting?the same as what抯 marketed as 揤isqueen??The reason I抦 asking is that people have told me certain thicknesses of Visqueen are waterproof, but actually would be air-porous in a vacuum bagging situation, which may explain why your pump ran continuously. Does anyone know of a membrane that is somewhere between thin poly and expensive vinyl? What tape works best for a one-off bag?


From contributor K:
To the original questioner: I have used other types of plastic films just taped together with carpet tape, as described above. If there are any gaps between parts or edges of pattern and high stack of parts where the bag has to really stretch across a span, you should expect an implosion if the PSI on the surface of the bag exceeds the strength of the chosen film, but you could use film as thin as a laundry bag from the cleaners if it totally conforms to the surface.

Some of the poly films that I have used had to be cleaned with acetone to get the tape to stick, then it seemed barely adequate, but by the end of the cycle, it could not be removed. Also, use cautions or dull any sharp corners.



The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor T:
I use clear shower curtains for a vacuum bag. They come in 60 x 72 inch sheets. I trim off the brass rings and stick the suction cups on the outside of the bag. I seal the edges with swimming pool liner repair cement. The only drawback is the bag tends to seal very quick around the valve stem before the entire bag is under vacuum. 30 x 24 areas are no problem, though. Since the bag is so cheap, I have several made and have 4 or 5 bags under vacuum at one time. Just pinch off the hose with a "C" clamp and remove the hose from the pump. My bags hold vacuum overnight. Larger bag can be assembled from several curtains. They are only 10 mil vinyl but seem to last a few years for me.

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