Vacuum Bagging Long Slender Solid Wood Shapes

Advice on using vacuum-bag clamping to glue up a long turning blank out of slender wedges. September 29, 2010

Question
I am gluing up approx 3" diameter by 40" long turning billets using 10 "pie" shaped pieces (like a pizza) and I am using a two part epoxy. I would like to know if it is possible to clamp this assembly using a vacuum bag system. Has anyone had any experience with this? I am aware that vacuum bagging is usually used for veneers.

Forum Responses
(Adhesive Forum)
From contributor E:
The Knowledge Base article below may be of help to you. I had to redesign a pie shape top. Iím not sure you are in the same boat but itís worth a look.

Sunburst



From the original questioner:
Thanks Contributor E. The problems inherent in the sunburst would not come into play here. As I said, my pie is only 3" in diameter and epoxied and 40" long to boot. Movement is a non issue. Hopefully, someone has had some experience with vacuum bagging solid wood parts. The "staves" are just over .75" to 0" at the center.


From contributor A:
Vacuum bagging is not used only for veneer. We vacuum bag entire 60' boats in one suck. They sell vacuum bag socks for applications like yours. They are lengths of tubes of various diameters. The layup technique is glue the staves wrap them together with 3/4" fiberglass reinforced packing tape. Stick it in the bag or tube and suck it. Typically you can get adequate clamping force with several ratcheting band clamps - same method tape then clamp. We've got vacuum and clamps. I would try the clamps first.



From the original questioner:
Thanks Contributor A. That is what I thought but I wasn't sure. I assume that the vacuum would supply sufficient clamping force, right? I am now machining the stave that they will have sufficient epoxy (10 mils) in the joint regardless of clamping force. That was the problem with hose clamps, too much force and some starved joints. Can you tell me a resource on the tubes and vacuum supplies?


From contributor A:
Just for this one project you'll have to throw upwards of $400-$500. $300 plus for a small less expensive vacuum pump. A bunch of hose fittings, gauges, etc might set you back another $50-$100. The bag film, breather fabric, peel ply, and mastic tape will get you another $50-100. I often purchase these product from Jamestown Marine Supply or LBI.com. You will find uses in the future for these tools. You can also buy an actual vacuum bag instead of making your own.


From contributor R:
If clamps give you too much clamping force, try tape and then wrap with surgical tubing.


From contributor K:
I have vacuumed plenty of unusual shapes, and it should be fine for this, but I am not sure you need it here either. You could just wind around it with a stretch packing wrap. As for the pressure when vacuuming, you will get approximately one psi for each 2" of mercury. As for the plastic tube, there are some other options worth checking. Some of my suppliers keep a roll of the stuff, which can be used to make short bags for assorted small parts, also for the food industry.


From contributor B:
Check out www.joewoodworker.com. The site has a ton of useful info regarding vacuum bagging and offers instructions and supplies to build your own setup. I just built a vacuum press using a compressor and the thing works great. Pulls 21" which is more than enough for what you need.


From contributor F:
Yes this is possible. Use a polyethylene plastic tube like a freezer shrink bag. Stick a rubber band on one end and double it over a few times and put the vacuum generator tube into the other end. Think outside the box and a lot of neat forms can be done with free form poly bags and a vacuum.