In our Belite ultralight aircraft, we occasionally make and use a carbon fiber / plywood laminate. This makes a very nice looking and strong panel, yet is very thin. It is capable of holding a lot of load when suspended across a frame, for instance, a seat bottom. (Double sided applications would probably be used with other cores than thin plywood.)
I recently made some of this magic thin carbon fiber / plywood. I documented the production steps so you can see how we do it.
In order to do this, we'll use some thick beveled glass, tacky tape, a vacuum pump and some vacuum tubing, bagging film, peel & ply film, fluffy cloth padding, epoxy, and of course, -- carbon fiber and plywood.
Let's start with a nice sheet of beveled plate glass. We've cleaned it thoroughly (I mean it, thoroughly!!!) and have lined the edges with tacky tape. It has been waxed, then the glass has been sprayed with film release, and I've run some plastic vacuum tubing along one edge, secured with tacky tape as well.
Warning: carbon fiber and epoxy and glass can be nasty stuff -- always use breathing protection, along with protective gloves. Use these instructions, as always, at your own risk.
Let's get going...
|Plate glass, cleaned and prepared for use.|
|Mold release, special wax, and tacky tape|
|Vacuum tubing, with notches cut into it every few inches|
|Generic vacuum pump, attached to tubing.|
|Closeup of tacky tape in corner, holding vacuum tube down|
|Bag Film attached to tacky tape on one side, then flopped over side of table.|
|Second strip of tacky tape, along with peel ply film placed to tape|
We don't use fancy carbon fiber, just inexpensive industrial 3K weight and plain weave. The number of layers is dependent on the application. For seat bottoms, 2 layers work well.
|Carbon Fiber cloth (3K, plain weave) doubled over to correct size|
|Plywood, 1/8", 2' x 4' size|
|Carbon Fiber (doubled) placed over dry plywood.|
Now I mix up some epoxy. We use West Systems, with 'slow' or 'fast' depending on the temperature of ths shop, along with my patience. How much epoxy? Enough to thoroughly wet the carbon fiber cloth and leave puddles of epoxy; you'll have to figure it out as you try this process. I pour it on the cloth and move it around, gently, with a small paint brush. I am careful not to disturb the orientation of the carbon fiber as I brush in the epoxy. It will drag with the brush very easily, and is a pain to move back to a square orientation.
|A bunch of wet epoxy on the carbon fiber / plywood sandwich|
|Peel ply flipped onto wet epoxy.|
Now I take some puffy cloth and put two layers on top of the peel film. It's purpose is to allow epoxy to squeeze up through the peel ply and into the puffy cloth. (Puffy cloth == high fill, non woven polyester)
|Two layers of puffy cloth over the peel film|
|More Puffy Cloth near vacuum tubing|
|Bagging film pulled over the entire assembly.|
|The vacuum pump is then turned on. You can see it suck the bagging film down almost immediately.|
|This is how it looks after a few minutes. The epoxy is being sucked through the peel ply, into the puffy cloth.|
|The film had a couple of leaks. I fixed them with blobs of tacky tape.|
At this point, I left the vacuum pump on and left the whole thing setting and curing. When I came in the next morning, I removed the green bagging film. It was easy to do; it didn't stick to anything. All of the epoxy below is fully cured:
|Bagging film removed, revealing cured epoxy throughout puffy cloth|
|Removing the peel ply and excess cured epoxy|
|Closeup of carbon fiber, note white dots (from peel & ply holes)|
|The carbon fiber / plywood is nearly ready to use|
And then all I have to do is trim off the edges using a band saw. Here's the finished panel, ready to use:
|Carbon Fiber bonded to plywood|
I hope you found this helpful!
-- James Wiebe, 2011 EAA August Raspet recipient