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Building Tips and technical articles. => Building techniques => Topic started by: Martin Gallant on September 23, 2010, 11:27:52 AM
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Hello,
I'm new to dope finishes, and need help before I make a mess.
When I cover with Monokote/Ultracote and glue on the tail section after covering,
I need to cut back the covering down to the bare wood at the glue joint so the epoxy has something to bite into.
Do I need to do the same thing (peel back the covering) with Silk and nitrate dope?
Or will the epoxy penetrate through the dope and give a good joint?
Should I mask off this area when prepping for silk, and make sure I don’t dope that section of wood?
FWIW, I'm using 5mm habotai silk from Dharma, Randolph Nitrate dope and thinner, and West System epoxy.
I'm going to glue a test piece later today, but was wondering what the the accepted process is here.
Thanks in advance!
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Just like with the 'coats, the epoxy will stick just fine to the covering, and the covering will stick to the wood like, well, covering.
So yes, you need to strip back to bare wood where you're going to glue on flight surfaces. Even if it's just paint you need to do this, for the same reason.
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I guess I do it the hard way. I cover after the plane has been assembled. The epoxy and cloth go inside the fuselage/wing joint before the top/bottom blocks go on. On profiles I usually don't cover until the wing and stab are glued in. H^^
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Referring to my original question, I built a test piece and allowed the epoxy to cure 36 hours.
Cutting around, and peeling off the silk where the glue joint will be is the way to go.
The resulting joint was much stronger than the application would ever require.
When stressed to failure, wood gave way before the glue joint let loose.
Thanks to the responders for putting me in the right direction.
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There was an aticle years ago abut glue joints and glue. A lot depends on the type of joint and use. I can remember covering combat wings completely before gluing the tail booms on. Same with engne mounts. Of course the engine mounts usually had a dowel down thru the mount and leading edge. Never had one come loose from the covering.
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I guess I do it the hard way. I cover after the plane has been assembled.
That's certainly going to lead to a better looking plane. The last profile I built I put the wings in and made nice fillets, painted, then covered the rest of the wings and the tail, then glued the tail on.
But it doesn't look as good as if I'd designed the tail to be covered after the fact, and assembled all first. (In particular, the dribble of epoxy on the fuselage under the tail is kinda embarrassing.) Fortunately, the plane was mostly built for performance; I'll worry about looks when I can fly the whole pattern!
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That is the way I was told when I first started flying. Worry about finish after you can fly your best. Also concentrate on building light and straight. H^^