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Old Sep 18, 2014, 07:28 AM
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Taxus812's Avatar
United States, CT, Windsor
Joined Apr 2014
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Question
Taping wing joints

Morning I am looking for some advice on the best way to tape a wing joint.

I am building an AlienAircraft Arrowmaster 55. (I'm blogging the build here http://www.rcgroups.com/forums/showthread.php?t=2244104). It basically is my first kit build (two when I was young)


There is a step where you tape the wing joints with cloth and secure it with thin CA. It comes out nice enough but it took a lot of filler work to make it smooth.
http://www.rcgroups.com/forums/attac...mentid=7103094


I have two more joints to do on the top wing. I was wondering if there is a better way to finish this joint (speaking with Tom Herr the tape is needed)
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Last edited by Taxus812; Sep 18, 2014 at 08:08 AM.
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Old Sep 18, 2014, 11:08 AM
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rcav8r2's Avatar
United States, PA, Beaver
Joined Sep 2001
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I typically just feather the joint with some joint compound. Get the stuff at the hardware store that the tub feels empty when you pick it up. Significantly less $$ than the hobby store stuff, and IMO works better.
Work in thin layers for best results. I don't worry about finishing the part that will not be exposed. I.E. the part of the wing that is hidden by the fuselage.

A tip to keep the joint compound from drying out. Take a paper towel and wet it with rubbing alcohol. Then place it on top of the stuff before closing the lid. Just don't let the paper towel interfere with the lid making a seal. Don't use water as it will start to mold before too long.
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Old Sep 18, 2014, 11:50 AM
Life is a Hobby
Canada, ON, Delhi
Joined Aug 2012
956 Posts
Use a fibreglass strip, not nylon. Nylon frays when sanded. Fibreglass does not.

Bill
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Old Sep 18, 2014, 12:53 PM
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mrittinger's Avatar
United States, MI, Roseville
Joined Dec 2000
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I lay it in place and tack on each end w ca, then run masking tape about 1/2" outside of it. Use finishing resin applied w a credit card and remove masking tape. Feather edge w sanding and a little filler if needed.
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Old Sep 18, 2014, 01:00 PM
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Taxus812's Avatar
United States, CT, Windsor
Joined Apr 2014
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Quote:
Originally Posted by mrittinger View Post
I lay it in place and tack on each end w ca, then run masking tape about 1/2" outside of it. Use finishing resin applied w a credit card and remove masking tape. Feather edge w sanding and a little filler if needed.
Because I'm a novice

What is finishing resin ?
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Old Sep 18, 2014, 05:51 PM
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United States, NJ, Woodstown
Joined Sep 2011
131 Posts
another vote for finishing resin....here's one readily available

http://www.lmii.com/products/finishi...inishing-resin
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Old Sep 19, 2014, 12:57 PM
ARFs make me BARF
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United States, MI, Roseville
Joined Dec 2000
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Pacer (zap) makes an epoxy finishing resin. Its a 2 part epoxy resin used primarily for finishing fiberglass. I like to use it because it dries slower and penetrates the wood. Once I have it spread through the reinforcing cloth, I hit it with a heat gun and it thins nicely and soaks in.
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Old Sep 19, 2014, 01:24 PM
The Junk Man
Jacksonville, Florida
Joined Jul 2006
1,678 Posts
I use the same resin I use to build with... ADTECH 820 resin with whichever hardener fits the job.

Any laminating resin can be used as a "finishing" resin. I like ADTECH because of its thin viscosity.

Tom
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Old Sep 19, 2014, 02:15 PM
David
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United States, TX, Houston
Joined Mar 2012
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We've all seen the guy at the field with a patch job that remains sticky forever and he claims he got a bad batch...

Certain resins will not cure in the presence of air. This doesn't matter much when used in lamination since it is sealed between layers of wood - nor if it will be used in multiple applications because the next layer will seal it allowing the cure to continue. The final coat, however, will be exposed to air where a finishing resin is used. The difference is that they add a small amount of parafin wax to the formula which rises to the surface to seal it from the air.

I've heard that you can seal off your work with saran wrap to keep the air out if you must use regular laminating resin.

I'm no expert and if what I'm saying here is wrong, I don't mind being set straight.
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Old Sep 19, 2014, 02:22 PM
Life is a Hobby
Canada, ON, Delhi
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Never had a problem with Bob Smith finishing epoxy curing when exposed to air. It is colourless and sands easily to a finer powder.
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Old Sep 19, 2014, 02:31 PM
The Junk Man
Jacksonville, Florida
Joined Jul 2006
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Quote:
Originally Posted by dmarusa View Post
We've all seen the guy at the field with a patch job that remains sticky forever and he claims he got a bad batch...
If he was using epoxy he almost certainly did not mix it properly.

Quote:
Certain resins will not cure in the presence of air.
Those cautions are for polyester resin, which is seldom used in modeling now.

All standard epoxies, ADTECH, Pro-Set, WEST, System Three, etc. will cure just fine in the presence of air.

Tom
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Old Sep 19, 2014, 02:39 PM
David
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Thanks. Like I said, I appreciate being set straight when I've got something wrong. - David
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Old Sep 30, 2014, 09:48 PM
Registered User
United States, NM, Hobbs
Joined Oct 2011
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Finishing resins typically have a lower viscosity and slower cure time than 5/15/30 minute epoxies. They are still epoxies, though. Epoxy can be covered with polyester resin and the polyester will cure. Most epoxies will not cure if put over polyester resins.

That said, I have had good luck with WEST epoxy repairing or modifying fiberglass boats. I had a sailboat with a hull thickness of about 7/8" in the spot where I wanted to eliminate a through hull fitting. I ground the area around the hole to a thin edge and laid up MANY layers of cloth and mat and it cured just fine. It even held through Katrina. Can't say the same for the rest of the boat, though.

David
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Old Sep 30, 2014, 11:11 PM
The Junk Man
Jacksonville, Florida
Joined Jul 2006
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Quote:
Originally Posted by David2011 View Post
Epoxy can be covered with polyester resin and the polyester will cure. Most epoxies will not cure if put over polyester resins.
Um, David... ya got that backwards mate. Epoxy will cure just fine over polyester.

Tom
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Old Today, 07:09 AM
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Tucson
Joined Nov 2009
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Yeah, I just built that same kit, and the nylon tape that comes in it sits up high for all to see, when it is painted.

Another comment - I don't that a 15cc OS GT-15 gas engine is going to fly this biplane. I should have used a GT-22 22cc gas engine.
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