TOMMYSTA

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Hi guys
If some of you could please talk me through how to do a at home vacuum bagging system I would appreciate. Here's what I got, I made a foam male plug of a wing. I haven't glassed it or anything yet. What I'd like to do is to make a top cover from this plug, the center section of an AT6 wing where the front wheel wells are integrated with the airfoil. I've been reading stuff on the internet and frankly I dont understand anything about a release film, breather layer. I have access to a vac pump with a regulator. I thought I could just cover the foam plug with a plastic shrink covering to act as a barrier and release layer, lay up my layers of cloth/mat and put in a bag and pull about 16-18"'s of vac and let it cure. But after reading a bit it sounds a bit more invlolved.
Any help would be greatly appreciated.
Thanks
Tom

Wazmo

I haven't bagged before, but have done some reading.
Release film, usually mylar, is used to prevent the skin from sticking to the vacuum bag. Often you lay out your glass and resin on the release film before applying it to the core (film side out, of course).
Breather layer is a section of porous cloth used to allow the air to travel out of the bag through the vacuum port (where you attach the vacuum source). If you don't do this, the bag can get sealed around the vacuum port, preventing the uniform removal of air from the bag.

What is it you're trying to accomplish? Make a stand-alone skin replicating your airframe shape? Make a female mold? Usually you would just make a core, skin it, and bag it.

davidfee

There are lots of different ways of applying the basic technique of vacuum bagging. Different applications will require different materials. "Release" is a very broad term which applies to several different materials. Basically, it is something which the resin will not stick to, allowing you to separate the finished part from something else. The release can be wax, a plastic film, a porous layer such as film with a bunch of holes in it, or even a woven nylon or Teflon coated fiberglass release fabric. Breather material is generally a bulky synthetic mat, which provides a clear path for the air inside the bag to be pulled out through. Breather also absorbs any excess resin which is pulled through the release film. Even paper towels can be used for the breather (cheap).

It sounds like what you're trying to do is use your foam plug as a male mold and just lay the glass on the outside of that. This will work fine, and you should not need vacuum for this. In fact, it is rather difficult to vacuum bag extreme compound shapes, as the bag isn't all that stretchy. There are stretch bag materials available, but it is still limited.

If you can cover the foam plug with a low-temp iron-on film, then wax it, you should be good to go. Use small pieces of fabric to go over the compound areas. You will need to fill and sand the outer surface, but the only way around that is to make a full female mold.

-David

rraimonfl

David, I think you may have the answer to my problems. Actually as you suggested to Tom, I have a male mold to which I will lay the glass over. I was also looking for bagging, but I guessed just what you also suggested, that it will not be easy to obtain good results when having compound shapes, as I have. Now, here is my nightmare: How can I make the fiberglass to "stick" to the compound shapes? FYI, I am working in an XF35, and I have split the fuse in upper and under sides. Although the F-glass cloth can stretch to the shapes, it tends to "short cut" to a more straight shape (cross section view).
Richard

davidfee

Richard,
There are maybe 3-4 "tips" I can give you right off, for you to try out. The first is to use the cloth on the bias. That means the fibers are running +/-45 degrees rather than 90. The fabric is cut diagonally, in other words. The fibers will be much more able to conform to compound curves this way. (also maybe try the "crowsfoot weave" fabrics) Second, try smaller/cut pieces. Lay smaller pieces into the really difficult areas, then lay a bigger piece in on top to make up the rest of the shape. Another idea is to thicken the epoxy with some colloidal silica to make it more sticky, but this can impede wet-out a bit. A fourth idea is to lay in just a surface layer of very light glass (3/4 oz or so) and let it cure most of the way, or even all the way. Then spray a very light misting coat of spray adhesve like 3M-77 and stick the heavier glass to that. Then wet out with epoxy and blot up the excess as usual.

good luck,
-David

rraimonfl

David, Thank you for your suggestions. The idea of using lighter cloth seems extremelly interesting. In reference with the idea of running the fabrics at 45 deg., it worth to lay the fabric and see what happens.

Richard