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Old Jun 19, 2011, 09:57 AM
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30 min vs 5 min epoxy?

Is there any advantage to using 30 minute versus 5 minute epoxy besides the obvious working/parts positioning time that 30 minute allows? In terms of holding strength for the housebrand stuff I use frequently from Ace Hardware, they both seem to be relatively close in numbers.
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Old Jun 19, 2011, 10:07 AM
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It is the strength and open time. On porous materials the 30min will soak in much further and create a stronger bond.

Open time as you point out is a biggie too 5 min just does not allow much. I use 5 and 15 minute for most everything however. 15 mins gives me the open time for larger jobs and as you point out the strength is FAR above that of the materials generally being glued.

Mike
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Old Jun 19, 2011, 10:38 AM
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The reason I'm asking is this...

I'm looking at joing two wing halves together for a sailplane that incorporates a wing joiner that is 1/4" ply sandwiched between aluminum plates. Studying the construction of the wing joiner mostly has me convinced that it alone will keep the wings from folding. All of the parts fit together like a glove and there will be minimal, if any, alignment efforts needed once the wing halves are pushed together. I'm thinking 5 minute epoxy would be fine in this application with the addition of small holes drilled into the mating surfaces to allow for epoxy "fingers" to form once the surfaces are pressed together. I'm practically out of 30 minute and am quite a ways from the nearest source (1 hour drive).
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Old Jun 19, 2011, 10:44 AM
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Your issue there is open time. When joining wings I want lots of time for alignment. 5 min does not give that.
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Old Jun 19, 2011, 11:05 AM
Guz
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The other issue is that faster epoxy can be more "rubbery" than slower epoxy (depending on brand). Don't ask me how I know
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Old Jun 19, 2011, 11:37 AM
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I consider 5 - 15 minute epoxy field epoxy, epoxy for field repairs. (and in most cases THICK CA will work just as well).

Otherwise use 1 hour epoxy for shop work. Time shouldn't be an issue and you will love the extra working time, for adjustment, and wiping up the excess epoxy.

I would wait and get the 1 hour+ epoxy. You would hate for the 5 minute stuff to kick in after 2 minutes, which it sometimes does after you ALMOST have everything set.

J
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Old Jun 19, 2011, 11:37 AM
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Originally Posted by Guz View Post
The other issue is that faster epoxy can be more "rubbery" than slower epoxy (depending on brand). Don't ask me how I know
I have had similar results. Over time I've had 5 min. epoxy parts just peel off. If I need a quick bond I use CA, otherwise 30min epoxy. Also, I've been getting better, more consistent results using a .1 gram scale to measure out the epoxy mix.

- Norm
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Old Jun 19, 2011, 04:22 PM
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The slower the epoxy set up time, the stronger it is. When epoxy cures it builds a molecular chain and the slower the cure, the longer the chain which increases strength. It has nothing to do with the soak in bit as that is a function of viscosity, the lower the viscosity the more apt to penetrate deeper into a medium. The strength is not a matter of penetration but of the molecular adhesion between the molecules of the glue and the structure it is binding to.
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Old Jun 19, 2011, 07:33 PM
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The strength is not a matter of penetration but of the molecular adhesion between the molecules of the glue and the structure it is binding to.
Really - source please?

To be honest Epoxy is well stronger than the materials we generally bond with it so likely a bit irrelevant. But I taught it had to do with penetration in the material.

I have read a number of woodworking sites and your the first to have that position.

Mike
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Old Jun 19, 2011, 11:15 PM
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5-15min for minor repairs & uncritical "epoxy" work. EX fuel proofing the firewall & engine bay

30-45-60min for anything requiring "epoxy" strength. EX wing halves & fiberglass/CF wing wraps, firewall installation, anything having anything to do with wing bolts/rubber bands, landing gear (from mounts to wire wraps).
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Old Jun 20, 2011, 10:25 AM
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Really - source please?

To be honest Epoxy is well stronger than the materials we generally bond with it so likely a bit irrelevant. But I taught it had to do with penetration in the material.

I have read a number of woodworking sites and your the first to have that position.

Mike
One of the better sources is "Handbook of adhesive technology" by Antonia Pizzi & K.L. Mittal. Adhesives can be a lot of different things so there is a gigantic amount of data to try to describe all types. The epoxies are one of the ones more dependent on molecular structure and attraction than many of the others.
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Old Jun 20, 2011, 01:58 PM
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Quote:
Originally Posted by silentsoar View Post
The reason I'm asking is this...

I'm looking at joing two wing halves together for a sailplane that incorporates a wing joiner that is 1/4" ply sandwiched between aluminum plates. Studying the construction of the wing joiner mostly has me convinced that it alone will keep the wings from folding. All of the parts fit together like a glove and there will be minimal, if any, alignment efforts needed once the wing halves are pushed together.......
It sounds to me as if this wing is meant to be left as two parts which slide together each time you want to fly the model.

If so you don't want to glue the wings together at the joiner. The wings are intended to come apart for easier transportation.

Perhaps post a picture of the parts and re-read the instructions?
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Old Aug 19, 2011, 08:58 AM
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I have started a build with Gorilla 5 minute epoxy. (An ARF)

It does set a might quick, and it does seem to dry with a skosh of give vs. being rock-hard, what's interesting is it has a quick 'set' but a 90-minute cure.

It does have a nice few minutes where it is 'gummy' and you can scrape the excess off.

Well, if you see 2 wing halves from a Flightstar 40 fluttering down a few moments after hearing "Crap! ... THUMP" you'll know what happened.

Dave
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