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Old Nov 29, 2012, 06:14 PM
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Congress, AZ
Joined Sep 2001
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" stuff cures hard as a rock AND resilient"

Well, that would require a rock be flexible right? None of those rocks out west

On the subject of thinning: Mark Drela suggest thinning epoxy with Denatured alcohol when using it to repair delaminated wings. He said the DA will evaporate and there is not apparent loss of strength. To each their own, I guess, but if the epoxy is used in a thick layer, maybe it doesn't let the DA evaporate.

For what it's worth.

Gary
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Old Nov 29, 2012, 09:48 PM
Hey was that a Thermal ????
Joined Nov 2009
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Gary,

OUR rocks are flexible.....they can go liberal or conservative.....and in the end they are still dumb as a brick.

Mark normally knows his stuff. I really didn't see how the thinning would hurt anything because in the end you still have just the epoxy once it cures.

Paul
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Old Nov 29, 2012, 10:03 PM
It's a mere flesh wound!
Buddy Roos's Avatar
Woodstock,Ga.
Joined Jun 2004
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Quote:
Originally Posted by The_Builder View Post
I know of folks, not me mind you , who have used foam safe CA to wet out the glass on the center wing joint. Don't get so hung up on the shaft we miss the point.

PaulLuap ( I don't know whether I am coming or going)
I've used Thin Foam Safe CA to wet out the glass on the center wing joint on more than 20 DLGs without any problems. I do lightly sand the area of the wing where the center joint glass is going to go.

Buddy
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Old Nov 29, 2012, 11:21 PM
Hey was that a Thermal ????
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See I told you I knew someone....

Paul
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Old Nov 30, 2012, 02:32 AM
Ride, Surf, Fly, Sleep
Joined Dec 2007
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Originally Posted by The_Builder View Post
Gary,
I really didn't see how the thinning would hurt anything because in the end you still have just the epoxy once it cures.
You're right as if used properly there shouldn't be any thinner left after cure.

The slight loss of strength when using thinners is all to do with the chemistry (at least it was with circa 2000 systems on the A380). Hardener and resin molecules react to form a long "twisty" polymer chain, the longer and twistier the better. Stick in anything that increases the distance between molecules during the cure and they won't be quite as long and twisty as they have less chance of coming together. Before someone says "what about polyforms and dynamic curve cures", yeah I know, but unless you have an programmable oven that's the simple explanation.

So additives do change the properties of the resin whatever they are and whether they are left behind or not (Thinners, whitener etc.). I've noticed many manufacturers claim this is not the case, but I can't see why the basic chemistry will have changed.

Got to say though in all practical applications (i.e. you're not making a real missile or A380) there is no difference. Using the correct cure temp curves (do any of us use temp curves?)and very accurate mixing (+/- 0.1 g) are far far more important for maximum strength- both of which as home builders we can't do well.

Bottom line - forget it and use a thinner or whitner if you want to!

Quote:
Originally Posted by The_Builder View Post
Gary,
OUR rocks are flexible.....they can go liberal or conservative.....and in the end they are still dumb as a brick.
Love the idea that you can grade the stupidity of masonry - rocks (dumb as bricks), bricks (dumb), Portland cement (some learning difficulties)
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Old Nov 30, 2012, 02:39 PM
Hey was that a Thermal ????
Joined Nov 2009
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Eventually my people will return for me. For the time being I just keep trying to fix stupid......banging my head against a brick wall made with Portland cement and set in bed rock.....
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Old Nov 30, 2012, 02:44 PM
Father of Fr3aK, DLG Pilot
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USA, OH, Worthington
Joined May 2002
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Brandon, the MGS stuff is quite a bit thinner than RR but it's also 3x the price shipped. I use both and love them both I also probably have 10 different epoxy blends in my shop at any given time.

(guess I'm wierd like that)

Most of the Fr3aK wings were joined at the center using CA rather than epoxy. Not all but most. It's fine.
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Old Nov 30, 2012, 03:19 PM
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Reno Nevada
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Eventually my people will return for me. For the time being I just keep trying to fix stupid......banging my head against a brick wall made with Portland cement and set in bed rock.....
When you "called home" you probably got a busy signal! they know better!
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Old Nov 30, 2012, 04:05 PM
Ride, Surf, Fly, Sleep
Joined Dec 2007
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Arrrgh - disaster!

Well it's not that bad really, but I got too cocky today and creased my FF's vert - missed the hand catch in a gust and had to put her down in the 'mole patch'.

Anyhoo - there's a small crack on the vert's LE and the skin has delaminated in a bubble to the TE. The thing is still rock solid and the spar's held fine. It doesn't look bad enough for a patch, but that delamination's a pain - anyone know whether CA will wick through the skin or am I going to have to inject it?

Damn those moles and their plane traps...one day I gonna fix 'em but good
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Old Nov 30, 2012, 04:55 PM
Father of Fr3aK, DLG Pilot
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USA, OH, Worthington
Joined May 2002
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CA will go right through unless the resin content is high or they're clear coated. I don't believe either to be the case with Pauls stuff. Check with Paul to ensure you can use regular CA. You may have to use foam safe.
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Old Nov 30, 2012, 05:28 PM
G_T
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Joined Apr 2009
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Though if you have some laminating resin you can do a better, lighter job. Generally you can rub (gloved finger) some epoxy through the skin. Rub gently! Then wipe and buff off all that you can. Do something to hold the skin in contact with the core, and wait. That's about it. Enough will go through to do the job, unless as Tom said it is epoxy rich or clear coated. Epoxy is lighter than CA and easier to control. It just takes more time.

If there is a clear coat or the original layup was wet (unlikely), then use a small straight pin to poke a grid of holes in the delam area. Then epoxy can get thru due to the rubbing.

Gerald
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Old Nov 30, 2012, 05:44 PM
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United States, GA, Atlanta
Joined Feb 2011
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Quote:
Originally Posted by tom43004 View Post
CA will go right through unless the resin content is high or they're clear coated. I don't believe either to be the case with Pauls stuff. Check with Paul to ensure you can use regular CA. You may have to use foam safe.
How bout it Paul? Can I fix a delamination by working it through the surface or do I need to use a needle to inject under the skin. Don't ask me why I need to know . Rich
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Old Nov 30, 2012, 09:03 PM
Hey was that a Thermal ????
Joined Nov 2009
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It will go through the skin just fine. If you are using CA use foam safe.

How about a game of Whack a mole ???!!!!

Paul
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Old Nov 30, 2012, 09:16 PM
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Will epoxy go through? Just want to clarify I was not going to use CA.
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Old Nov 30, 2012, 09:22 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
3,785 Posts
FWIW....

In the Balsa Builders forum there was a discussion about different glues. Some of it directed at edge joining balsa sheets. Just wait I'll get to the point Anyway the discussion was how hard it is to sand a CA joint and get a smooth surface. One MFG suggested you sand as soon as the joint is cured as as the CA continues to cure becoming harder and MORE BRITTLE over time.

My point is, maybe CA isn't all it's cracked up to be?????? No pun intended It may be, epoxy though slower, is really the better material for long term building and repairs. Yes I know in the heat of a contest you may have no choice but to use CA.

Ken
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