Best Method for Getting "Clean" Edge on Fiberglass Canopy Fairing

[tx_jayhawk]

OK...I have sanded and filled and sanded and filled the front canopy fairing to where I think it is in pretty good shape.

My quesiton is this....what it the best method for getting a nice unoform edge at the plexi transition? The instructions say to sand it done with 150 grit until it is about the same thickness of the 1st layer of tape, but that seems to result in "fraying" the fiberglass edge so that it is not uniform. If I build it up with epoxy/micro or smooth prime, it looks better but will be much thicker (can't get it down to one tape layer.

Should I...

- Not worry about getting a "thin" ledge at the transition and focus more on consistent edge with approrpriate filler?
- Sand through all the tape at the edge and fill back up and resand filler only?

Any other thoughts?

Thanks,
Scott
7A Finishing

[kentb]

I had two layers of tape (black electric tape). I sanded until I was removing black from the first layer. Then I removed that one and sanded some more until is was just starting to remove more black using about 200 grit paper. I removed the last layer of tape.
When I masked for painting I taped so that the edge would get paint on it and just a little on the plexi.

Kent

[Norman CYYJ]

I use two layers of electrical tape at the transition. Sand the glass till it is smooth with the second layer and then after you have everything sanded the way you want remove the second layer and very carefully sand the transition again lightly. Remove the first layer of tape and the paint will fill the small edge remaining. Use two different colours that way you can tell if you are too agressive with you sanding if you break thru to the second colour.

[f1rocket]

Cover the area with plastic, make the layups, and then remove the entire assembly from the airplane and finish it on your workbench. THEN, use some proseal to glue it back in place.

You'll get a perfect finish, won't screw up your plexi, and you won't have to spend days or weeks applying bondo to your airframe to smooth the transition. I even applied mine with rivets so it looks like a piece of aluminum.

[tx_jayhawk]

OK, it sounds like others are relying on the paint to make a "clean" edge? When carefully sanding down to the 1st layer of tape, you start to get into the fiberglass esge and there is some natural fraying that occurs.

Maybe I shouldn't worry about it and the paint will hide it? Or, am I being too picky?

Scott
7A Finishing

[scard]

Originally Posted by tx_jayhawk

OK, it sounds like others are relying on the paint to make a "clean" edge? When carefully sanding down to the 1st layer of tape, you start to get into the fiberglass esge and there is some natural fraying that occurs.

Maybe I shouldn't worry about it and the paint will hide it? Or, am I being too picky?

Yeah, what you have found is that you can't perfectly feather a fiberglass layer. A little bit of filler beyond the edge of the fiberglass does the trick. That is how to bevel down from the thickness of the last layer of glass to a near smooth edge.

[DanH]

Lotta ways to skin a cat.

3M blue vinyl masking tape resists sanding better than anything else I've seen. Sand the fiberglass edge down flush with the tape using a small (2") block to keep things flat. When you have it like you want it, pull the blue tape and replace it with 1/4" 3M fine line tape, which you can pull to a nice straight-edge line. Lay it down just a fuzz away from the existing glasswork, which you might need to do anyway to get your edge really straight and even. Now mix about ten grams of West System with slow hardener and add cabosil to thicken. Use a narrow squeegee to wipe it on, filling the sanded glass surface and the tiny gap between the tape and the glass. When done, immediately pull the tape while the epoxy is uncured. You'll get a nice edge. After cure again lay down some blue tape to protect the plexi and you can lightly block sand the area. It should now be ready for paint prep, and probably won't have any pinholes.