whats the difference between 6 minute and 30 minute epoxy as far as the strength

30-minute is definitely stronger than 5/6 minute epoxy. 30 minute epoxy has more time to work into the pores of the material that you are joining than 5 minute epoxy, and therefore will give you a stronger bond. I very rarely use 5 or 6 minute epoxy for anything I do. I use the 30 minute epoxy almost exclusively because it's stronger.

Ken

Night and day sometimes.

A great amount of the strength of a joint is from the glue penetration. The glue will be as strong as it'll get no matter what, but the joint is only as strong as how deep the glue gets before it quits penetrating.

I mix my glue on note cards. The 6 minute can be peeled from the card when cured. The 30 minute penetrates a couple of cards and no way to peel it off. Both blobs are just as strong. But the glue joints they make are as different as night and day.

I use NHP 30 minute for building, and I find that it sets up a lot faster than advertised. I'd say I get a working time of 5 minutes or less, which is perfect for most of what I do. I mix it in medicine cups, which may lead to the quick setup - a lot of heat builds up. When you spread it out, like for 'glassing a wing joint, it takes much longer to setup.

I got some NHP 5 minute to throw in my box for field repairs. The first thing I noticed is that it smells terrible. The 30 minute has no odor, the 5 minute smells like crap. I have only used it for small repairs, but it has held pretty well.

24 minutes..

Ok... i'm serious now

I bought a whole lot of 5 min. epoxy and it is super strong. The joint is actually stronger than the material you are glue together.

I don't know about 30 min. epoxy.....I can't hold it for that long.

da Rock's got it. The 30 minute is more penetrating into wood and other porus materials. It "wets out" better. It also has longer to link before it kicks and you get a more consistant result. Epoxy worls because the molecules form long chains. The longer it is "free" the longer the chains and the stronger the bond. I don't use anything faster than 30 minutes. Some of the West System epoxy I use is "120 minute". At that rate the amine waxes have a chance to float to the surface and you get a glassy result when hard.

And if you're going to epoxy a joint and have to hold it while the epoxy sets, you're screwing the strength of that joint from what it could be.

If you want a strong joint in a very short time, use CA. It's also lighter buy a huge margin. And is going to be stronger than 5minute by a huge margin.

One of the other benefits of 30minute epoxy is that after you've glued the joint and stabilized the pieces (masking tape for example, is a wonderful building tool) you can wipe the excess epoxy that's squeezed out of the joint. That reduces the weight added by the epoxy to usually less than half it'd be if you left the worthless excess. Very, very seldom are fillets of epoxy worth the weight penalty.

The main reason for the added strength of the slower epoxys is NOT that fact it soaks in further but because the molecular chains formed as it cures are longer in the slower curing mixes. This is what increases the strength. Of course, if you tried to put 5 minute epoxy that is already starting to cure in a joint, it will be weaker because of how well it binds with the material being joined so (it soaks in better) is partially true but not the full story.

That is the reason for the epoxy being stronger, not the joint.

If any glue soaks twice as far into the wood and then hardens like epoxy, you've really got an excellent joint. Because very often the exterior area surrounding the epoxy is a function of how far it penetrates. And if you can double the area being held (by the epoxy in this case) you've more than doubled the strengthened area around the joint. The epoxy in the immediate joint area is going to be massively stronger than the wood whether it's 5minute or 30minute. What you're gaining from the extra penetration is a significant area of strengthening of the wood that supports the joint or the joint supports.

Truth is, epoxy isn't the best choice for the majority of joints in our models. However, the places it's good for are areas that benefit from area strengthening, like firewalls. and that brings another point.........

so let me ask this im glueing together the wings on a sky raider m 1 would i be better off to get 3 hour epoxy to be sure of a better hold also is it a good practice to always put milled fiberglass in your epoxy? and lastly do you always mix your epoxy 50/50 or a little more hardner or a little more resin? starting to build my first plane so sorry for the kinda simple questions but i just want to be sure!!!

The firewalls in what might be all of the ARFs nowadays is liteply. Yeah, LITEPLY, which is actually plywood in name only. It's a somewhat strong, light wood layer with a veneer layer on either side. You can usually break it with your hands. It often has weak grain running through the single thickness of the center wood. And ARFs nowadays use two pieces sandwiched together for firewalls. Hey, it works ok for awhile if nothing much happens to it, right.

Stick something to it with 5minute and the epoxy might not even penetrate the veneer. It'll stick to it no problem, but 30minute often penetrates and sticks the veneer to the center better than it was glued in the "plywood" plant.

Penetration is one of the huge reasons to use epoxy. It does more than stick two pieces together.

First of all, you don't have to use 3hour to get excellent results from epoxy. It's kewl to use it and ought to penetrate better than 30minute, but that's about it. Somewhat better. But both are hugely better than 5minute.

As for putting milled fiberglass into epoxy to give it a better hold, it doesn't. Glass, kevlar, carbon fiber, and the likes are used to produce structural support or provide additional surface thickness. The glue is what holds things together.

You mix epoxy exactly the way the instructions say. As well as you can, get the proportions sized according to the instructions. Anything else wastes epoxy and can cause problems. The two parts are two different materials that are produced at the factory to cure perfectly if you get their proportions close. They won't do better mixed incorrectly.

It's good stuff. Use it the way the instructions say and it'll do wonders for you.

Very often, epoxies are made for somewhat specialized purposes.

If you've got some 3 hour you might read it's label or enclosed literature to see what it was made to do specifically. You might find that it was for layups or glasscloth molding. Or as surfacing resin, also called finishing resin.

For our models, 15 and 30 minute are excellent. And are usually made to be glue for assembling structure. The 30 is really good for reinforcing cowls and such with glasscloth, as well as doing a great job of gluing firewall bracing and such, or joining wing halves.

30minute is often the best value for the expense. I just used up the last of some I bought a year and a half ago, and in that time have built over 15 ARFs. And repaired a number of them. And doubled about half the cowls in that bunch.

As you get experience using it, you'll get good at squeezing out just the amount you need. And won't be wasting any, and certainly not wasting the blobs that kick on you before you can get it all applied.

as far as applying the epoxy to the wing halves what is your method and so you are saying there is no good reason to use the milled fiberglass?

Milled fiberglass will add shear strength. Colloidal silica will make it thixotropic (a fancy word for syrup-like so it stays where it is put). Wood dust (aka wood flour) and microballons will also thicken and lighten it - for used as a filler or fillet. And also usually cause the epoxy to "kick" faster. Mix the epoxy plain first and then mix in the fillers before applying.

Gererally, anything you add should be for a specific reason. As a cement epoxy doesn't need anything. A better idea for wing halves is to bridge the seam with 1 oz. fiberglass cloth.

PS - don't clamp epoxy tightly as in white and yellow glues. You want a thickness between the parts, not mushed out. That's called a "starved" joint.

As Charlie P. suggests, there is a good reason to use it, but not in order to glue wing halves more securely. They won't glue together any better with milled glass filler.

Specific to joining two wing halves together, it is unnecessary to use any filler as the joined area is very, very large. And getting a perfect mating of the two root ribs is actually unnecessary. It's good to try for, but not at all required. Most center wing structures do benefit from the perimeter of those ribs being attached directly and that's where epoxy gives excellent performance. So when you're joining wing halves, don't labor over getting the two ribs perfectly covered overall. Just make sure the outer edges are completely painted. And have the ribs around the spars and LE decently painted as well. But it's really unnecessary to work at getting 100% coverage.

One thing to always keep in mind when using epoxy for mostly balsa to balsa joints, is that even if you were to get a perfectly uniform 100% epoxy rib created between the two wing root wing ribs, that bulletproof new epoxy rib would simply be attached to balsa sheeting etc about 1/32" away. And if the joint has ply or aluminum or whatever in it, those materials are there in perfect amounts to provide all the strength the structure can handle, and the epoxy is just bonding agent.

So don't stress over laying in the epoxy. After all, every day people glue those same wings together with elmers and such. And those last excellently well too.

thank you very much for the detailed replies i understand epoxy pretty good now of all that was said the last sentence said all i need to know!!! i will for sure have more questions i know before i get the sky raider completed!!