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Epoxy Question

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Old 09-10-2004, 10:03 PM
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-pkh-
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Default Epoxy Question

This is a real newb question for ya...

I've just got 6min epoxy... my Avistar ARF kit specs 6min and 30min epoxy for different things. In all cases, it seems to me that I can get the parts together and positioned properly before the 6min epoxy sets... is there any reason to use 30min epoxy instead? Is it supposed to be stronger or something??
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Old 09-10-2004, 10:12 PM
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gus
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Default RE: Epoxy Question

Yes, 30min is stronger, for a number of reasons but the two principal ones are:
1) (I "know" this) the glue can "seep" deeper into the wood grain in 30 minutes than 6 minutes, giving a bond over a greater depth in the joint.
2) (I have "heard" this) the chemical reaction is cooler, slower, and the resulting chemical structures tend to be stronger because the chemical chans are longer.... (the person who told me this might have been talking from the wrong end....)

Regardless, it is generally acknowledged that 30min gives a better bond than 6 min. It is always recommended for more critical joints (Wing joining, firewalls, etc), wheras 6 min is mostly recommended for leass critical joints (servo trays, etc)..

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Old 09-10-2004, 10:24 PM
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Default RE: Epoxy Question

Ahhh... I see... Thanks, Gus!

I'm getting me some 30min epoxy, then...
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Old 09-11-2004, 07:55 AM
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Default RE: Epoxy Question

I have found that the wood will break before a good glue joint does when using either 5 or 30 min. epoxy.
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Old 09-11-2004, 09:40 AM
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Default RE: Epoxy Question

I'm not a highly experienced builder. I use only 30 minute, or slower, epoxy because I like the extra working time. I'm building a Tower Hobbies Uproar 60 and the instructions specifically say to use 6 minute to attach the firewall to the fuselage (every step that calls for epoxy recommends 6 minute). So far I have ignored the manual and used the slow stuff.
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Old 09-11-2004, 10:58 AM
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Rodney
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Default RE: Epoxy Question

Yes Gus, the slower epoxy form longer molecular chains and are stronger than the slower. I shy away from the fast epoxies (5 minute) for a number of reasons unless the repair is not structurally important and brittle joints aren't a problem. 5 minute has its place, it is just very limited. In case you do not know it, the fast epoxies take nearly as long as the slow ones to gain full strength, usually a matter of hours--not minutes. It is just that the tack period is shorter.
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Old 09-17-2004, 10:27 AM
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Default RE: Epoxy Question

HI GUYS, I thought I'd add my 2 cents. I Had 2 avistars, now I have 2 avistar wings. I flew them for 2 1/2 years and never had any problems with the wings. Both had the ply wing joiner and I used 15 min epoxy. I agree that 30 min is stronger and would even suggest using it but one thing I think needs to be mentioned is not so much how much or what epoxy but how you apply it. Maybe this goes without saying but when I glue critical joints like this I " double glue" In other words you apply an even coat to both surfaces. This may not be necessary with the new epoxies but I've been building for 30 years or more and these types of joints have never been a problem for me. I also let them set for a few minutes before joining. Both of my avistars gave me a lot of flying time. I made many great landings and enevitably, more then enough mistakes to put them in a trash bag but both wings survived. good luck with yours. Feep
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Old 09-17-2004, 10:36 AM
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Default RE: Epoxy Question

Well said Feep. The intent of using longer curing epoxy and / or applying it to both surfaces is to get it to soak into the wood a little bit. You can also use mill fiber to help with bonds.
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Old 09-17-2004, 10:50 AM
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Default RE: Epoxy Question

Use 30 minute whereever you need, work time is better for joining the wings and alligning the stab, but 45min -1hr will be even better. As the room is hotter in summers it cures a lot faster with 30 min, my working time is about 10-12 minutes now, and not enough for alligning things.

For proper allignment and cleaning things something more than 30 min will be better, 30 min or 45 min.
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