15 Min Epoxy

[Capt Pete]

I'm building my Launch Pad Hawk and right now the rocket is almost complete. The fins have been tacked on with 5 min Epoxy. I was going to start the fillets and found that I only have 15 min Epoxy. I checked my local Lowes and Home Depot and they didn't have any 30 min. I checked with my local hobby store and they were out. I could order some online which I'll need to do anyway. But I was wondering if I should use 15 min on the fillets since I have it.

Pete

 

[Missileman]

IMHO that is a mid power kit. 5 min is plenty but 15 min should do you just fine.

 

[DynaSoar]

Originally posted by Capt Pete
I'm building my Launch Pad Hawk and right now the rocket is almost complete. The fins have been tacked on with 5 min Epoxy. I was going to start the fillets and found that I only have 15 min Epoxy. I checked my local Lowes and Home Depot and they didn't have any 30 min. I checked with my local hobby store and they were out. I could order some online which I'll need to do anyway. But I was wondering if I should use 15 min on the fillets since I have it.

Pete

I never use anything but 5 minute, for everything. Why would fillets a need slow cure?

 

[rocketsonly]

Has anyone done a test on the different strengths of different time curing epoxies? Such as 5 min. vs. 15 min. vs. 30 min. vs. 60 min.?

 

[BlueNinja]

I believe since the slow has more time to set up, it is much stronger... 24 hour is really strong, i think, but I dunno whether the West system "tropical cure" hardner is stronger, although it takes like 3 ddays to cure from what I've heard.

 

[Hospital_Rocket]

Originally posted by rocketsonly
Has anyone done a test on the different strengths of different time curing epoxies? Such as 5 min. vs. 15 min. vs. 30 min. vs. 60 min.?

Try this out

https://www.rocketmaterials.org/

 

[rocketsonly]

Cool! They have lots of neat tests. Thanks for the website.

 

[lalligood]

Originally posted by DynaSoar
I never use anything but 5 minute, for everything. Why would fillets a need slow cure?

So that you have plenty of time to make them nice & smooth & save you the hassle of sanding them to shape. There ain't nothin' like pretty fillets on a rocket

 

[Stymye]

you won't find less than 30 min on that site,,

5 minute epoxy is like the velveeta of cheeses
it looks like cheese but thats where the comparison ends

but it does make easy fillets

 

[DynaSoar]

Originally posted by lalligood
So that you have plenty of time to make them nice & smooth & save you the hassle of sanding them to shape. There ain't nothin' like pretty fillets on a rocket

They come out nice and smooth due to fluid settling for me. I don't do anything to them after putting it on.

 

[DynaSoar]

Originally posted by stymye
5 minute epoxy is like the velveeta of cheeses
it looks like cheese but thats where the comparison ends

I don't understand what you mean. It says it's epoxy. It works like epoxy. Is there something specific that maes it inferior?

 

[dr wogz]

Quicker setting epoxy has something in it to make it cure in a shorter time. Dunno what that is, but it compremises the 'holding' power. Longer set time epoxies have less of 'that' stuff in it, making a stronger bond. Also, slower cure epoxy tends to 'wick into' materials better, giving a stronger bond. The longer cure time alllows the stuff to remain runny longer, allowing it to get into all those little nooks & crannies..

At least, that's what I've been told, and that's what I'm sticking to!

 

[DynaSoar]

Originally posted by Hospital_Rocket
Try this out

https://www.rocketmaterials.org/

I hate to be pendantic, except, no I don't, or I wouldn't have become a scientist.

There's no comparison there of similar formulations differing only in cure time. There's only comparison of different formulations, and the cure time for only one of those is mentioned.

The testing done for that site is truly some of the best I've seen relating to rocketry. Unfortunately people read stuff into the results that aren't intended.

Frinstance, they'll look at the bottom line and see that he says Aeropoxy has a slight edge in a certain application. They'll incorrectly conclude Aeropoxy is better for everything, and say so, and so others will say so, and so we have the process by which overbuilding becomes the norm. (That, plus the fact that building is part of the hobby and so some people just build the heck out of everything and enjoy themselves).

What the site doesn't tell you, and it doesn't intend to, is whether the results presented are meaningful to any given application. Without an understanding of what the effect being tested actually is, AND without a measurement of the applicable stress forces placed on a given design to compare the results against, people will jump to the conclusion that Aeropoxy is better than West Systems without cause. They very well could be correct in the same sense that a daisy cutter is better than a cruise missile for getting rid of the mosquitos in your yard, or alternatively, that a steak knife is better than a pizza cutter for chopping down trees.

Also, the testing done there is comparitive testing only, and has no controls. These are demonstrations, not experiments, and so the conclusions only represent themselves, not something generalizable. This is not to say this is a bad thing; Feynman's "proof" that O-ring failure due to cold killed the shuttle is a spectacular example of this sort of conclusion. It's just important for people to recognize that the results there are only the results of those particular tests in those particular conditions and nothing else, and that it's up to them to figure out if those conditions have anything to do with their particular questions and needs.

 

[Stymye]

yea that didn't make much sense, now that I look at it...lol
I mean for construction purposes

Strengthwise, it's probably the worst epoxy you could pick.
and to get the convienent 1 to1 mix ratio, alot of unnecessary stuff is added to the hardner, thats why brands like west system and others are not 1 to1 and considerably stronger, they are pure epoxy, the "real cheese" so to speak

the main benefit I see of using 5min over anything else is the nice fillets,, and I use it for that as well.but why not use 30 minute for anything else if it's the same price?

if you could by any grade of gasoline for the same price , what would you use?

I know it will hold modrocs together. but there again, yellow glue is so much stronger and lighter for those purposes and much easier to deal with and clean up

epoxy merely forms a "plastic" bond,,whereas, wood glues soaks into and actually links with the wood and paper fibers.

I'm not anti-epoxy by any means , but judging from some of the things I read here some people think any epoxy is the strongest glue known to mankind and any epoxy will make a superior bond to anything else. but there are VAST differences, hense the velveeta comment.

bottom line is , please use what works for you, but it doesn't hurt to know the differences. oh....and I do like Velveeta.!

 

[OARJeepr]

I'm new around here but I figured I'd jump right in.

If we're talking wood and paper then no way is epoxy really necessary. Yellow glue will form bond stronger than the materials being bonded. In other words if the glue joint fails with yellow glue its your fault not the glue.

So while I never use epoxy to attach balsa/plywood fins I am a fan of using it to fillet. Epoxy fillets just end up looking better for me. Yellow glue shrinks and leaves voids that i always have to fill. Epoxy doesn't. Besides I view all my low/mid power builds as practice for high power so I try to incorporate as many high power build techniques as practical.

Most importantly though use whatever adhesives make you happy and work for you. Doesn't really matter as long as the rocket flys.

 

[Missileman]

Welcome to TRF Bill,
That is what I was going to say.
Yes yellow glue for this bird is plenty strong but epoxy makes a better looking fillet, not to mention the time savings.
I have waited in excess of 3 hours, when the humidity is high, for yellow glue to dry enough to turn the rocket and do the next set of fins.
5 min. epoxy you can have all your fillets done inside of an hour.
Add microballoons to the equation and you can do all your fillets in one shot and they are easy to sand.

 

[DynaSoar]

Originally posted by stymye
yea that didn't make much sense, now that I look at it...lol
I mean for construction purposes

Strengthwise, it's probably the worst epoxy you could pick.

The only data available so far doesn't have anything to say one way or another on the subject. You assert that 5 minute is the weakest. Is there any data that supports that assertion?

I've got same data that says this one particular epoxy has an adhesive tensile lap shear strength (that's what's most important when it comes to keeping fins on a flying rocket) of 1600 p.s.i. on a 0.005" bond line. That's some very tough stuff. Reckon that's strong enough? That's Devcon's 1 minute cure epoxy gel.

Their 5 minute is 1900 p.s.i., and their 10 minute is 2400 p.s.i.
We can safely assume that the slower cure = greater shear strength isn't only related to their brand; it's probably all epoxy. These data do support the assertion.

However, the question remains, is 1600 p.s.i @ .005" bondline enough? Dollars to donuts 99% of people who'll say the slower cure is "better" don't know enough about the meaning of the measurement used to be able to say what "good" is, much less "good enough". For all they know, 1600 psi may be greater than the strength of the tube their using, meaning the body would bust before the bond.

An example of how silly things can get when people use numbers alone without understanding where they came from: Some time ago computer video cards went to 32 bit color, making them able to display 16.7 million colors. There are now cards out that can display over a billion colors. They cost a lot. People buy them. Obviously a billion colors is better than only 16.7 million. But can they really display that much? Who knows. The human eye can only distinguish at best 4.5 million colors.

A point I didn't make in the thread I started in Scratch Built, about the cluster design I'm working on, I'm doing it all with Estes strength tube stock, balsa fins, and wood glue. The two stage version, with 3 E boosters starting 3 E sustainers is going to push over 170 n/s, into the H range. I'm betting they'll hold together because the data say what I'm using is good enough. Of course, learning how to use it right for maximum effect is important. For everything else, there's slow cure epoxy.

 

[Hospital_Rocket]

Keep one thing in mind folks

If the joint is stronger than rhe surrounding material, you probably just moved the failure point...

 

[lalligood]

My hat is off to everyone that has contributed to this thread. It easily could have subverted to a "Tastes Great! Less Filling!"--I mean "Epoxy rules! Yellow wood glue is the best!" brouhaha...but thankfully never did. Instead we almost waxed poetic on the benefits of various adhesives that are useful--and WHEN they are useful--while keeping it cool.

Man, I love this place

 

[Mad Rocketeer]

jcrocket:

I'd love to see a set of tests like that!

What would be perfect would be to see most of the major and commonly used adhesives tested side by side on similar materials, showing how strong the bonds are and what breaks first, glue, cardboard, or wood, etc. The combinations might get prohibitive, so you'd probably have to stick to the "reasonable" combinations of plywood or balsa to paper or phenolic and so on, leaving off stuff like balsa to glassed phenolic. But the closer one could come to doing every common adhesive against every common joint type against every common pair of materials looking at every common type of stress the better. Probably take a lot of money. We could pass a hat once an estimate of cost was made.

Just thinking (dreaming) out loud.

 

[airwolfe1]

For doing great fillets, find West Systems 406 Colloidal Silica. This is an epoxy filler which allows the epoxy to maintain it's bonding properties while thickening it up. Mix it into a peanut butter consistancy and spread it along the joint, then after dipping a plastic spoon, in denatured alcohol, run the spoon down along the joint. You will have perfectly smooth and consistent fillets that require virtually no sanding. This tip was found on Jon Coker's web site:

https://www.jcrocket.com/quicktips.shtml

I've also mixed this Colloidal Silica into other types of epoxy ie. Devcon 2 ton and had really good results.

 

[airwolfe1]

JCROCKET ....thanks for your very useful web site... I recently purchased a seal-a-meal to try out your vacuum bagging technique.

 

[lalligood]

Originally posted by jcrocket
And personally, I add milled fiber to epoxy for fillets. It strengthens as well as thickens.

I'm a big fan of milled fiber mixed in my epoxy too. I use MF when making external fillets. Before anyone tries using MF though, you need to be comfortable with making epoxy fillets. It adds enough strength--not to mention makes the fillets so hard--that you can all but forget about sanding the fillets to shape after the epoxy cures. Gotta make 'em look pretty while the epoxy flows

 

[Mad Rocketeer]

Would it make sense to do a fillet in two layers? First layer is for strength, and the second is for smoothness. Could use something like the additives mentioned above in the inner (first) coat and intentionally leave the surface rough or etch it with a carbide etching tool if it got too smooth to cover well and not smooth enough to use as a final finish. Then use a finishing epoxy with no fillers to go over the inner coat and provide a smooth finish.

I'm thinking this might just result in unnecessary weight and not add enough extra strength to matter for most cases. After all, once the fillet is tougher than the material joined, the rest is just wasted mass, right? Maybe with one of those tough new plastic tubes and fiberglass fins it could help.

What do I know? I've never used epoxy on a rocket. Yet.