Glue Question

I have what I think are a few simple questions about the different glues people use.

First off, is this list correct in the strengths of glues going from weakest to stongest?

1. White glue (Elmers)
2. Yellow glue (Elmers Wood Glue)
3. CYA glues
4. Epoxy (5 min)
5. Epoxy (5+ min)

I have been doing LPR and have been using only yellow glue with CYA used in tacking on fins before fillets of yellow glue.

I have started using CYA to "paint" balsa fins. I am building a Fat Boy w/ a 24mm MMT now and will start my first mid-powered bird soon. (Aerotech Tomahawk). The instructions say to use medium thick CYA.

When should I upgrade to stronger glues? The yellow glue is obvioulsy very easy to work with. Should I use CYA on the Fat Boy? Can you do fillets with CYA or epoxy? Should I use CYA on the Tomahawk? Or go to epoxy? I've never used epoxy and am a little leery of it. I've read about fillers for use with epoxy like micro balloons. When do you need to use filler and what filler do you suggest? Where do I buy filler?

There might be some threads about this but I haven't been able to find them.

Thanks in advance for everyone's help!

Color me eager to learn...

bmhiii

well, that's why we're all here...

to learn and, when we can, to teach...

You list is fairly basic, but seems to be correct. Understand, however, that there is more to consider than just strength. You have to consider the materials being glued as well as the stresses that they are subject to.

For example, testing that I have done shows that CYA's are great for tacking fins in place, but that's about it (as far as fins go). Launch and boost vibration is too much for such a brittle glue and plain old white glue is, therefore, FAR stronger (overall) than any CYA for that application.

Also, as you point out, mixed properly the longer the rated cure time the stronger the epoxy (this is a generalization). Also, most all epoxy glues avail at your local hobby/hardware shop are considered low grade adhesives (even the best ones). Epoxy rated as "aircraft grade" are some of the best, but are very hard to fine and rather expensive.

I have never used fillers with epoxy as they tend to weaken the bond (but others may have more experience with newer fillers). Also, (unless there are new approaches...) the only time you *need* a filler is when you *want* to use less of the expensive epoxy. Although I imagine fillers also change the way the epoxy can be finished.

Hope this helps...

You in general have the right order in terms of strength. Here are some additional points to consider.

Like Jim said, the materials you use makes a big difference. A well reinforced joint useing carpenters glue can be very strong. There is a dude who is doing formal testing of HPR materials (link at bottom). The results are interesting.

Epoxy is an interesting animal as you have to worry about mixing, etc. Mix it wrong, and it might not be ast strong as yellow glue. If you use G10 fins, then epoxy is the only choice. When you use commercial epoxies such as West Systems, the epoxy is thin, and you may need fillers. For instance, using a thickening agent such as a silica thickener will keep more epoxy where you need it. System one recommends you first coat the joint with unfilled epoxy to let it soak in, and then thicken it and apply it to the joint. Structural fillers such as chopped fibers will add strenth to epoxy structures, and thus may make fillets stronger. Microballoons fill the epoxy, make it easier to sand, but weaken it. All this is somewhat moot with the Bob Smith epoxies, which aren't that thin, and are fine for most applications. I use these for a majority of my work. If you want to buy the 'better' epoxies, you can get them online and they are available from boating stores. Although the investment is higher, the cost of the epoxy is lower. On problem I've found is that it is impossible to mix 5:1 epoxy without pumps. Most of my jobs require a lot less that what is dispensed, so I find the Bob Smith more convenient.


follow this link to the strength of materials testing

Originally posted by rstaff3
On problem I've found is that it is impossible to mix 5:1 epoxy without pumps. Most of my jobs require a lot less that what is dispensed, so I find the Bob Smith more convenient.

Click to expand...

One way I've found to use less West Systems epoxy is to dispense each of the 2 components into 2 different graduated containers. Then I mix how much I need (in my case, half) into a 3rd container. Any leftovers, I pour back into the original containers.

The problem I've see is that the volume of one squirt of hardener is fairly small. With the graduated containers I have, cutting this even in half isn't that easy. This could be fixed by the right sized container, I suppose. Or even by going for my L3

Instead, I just try to arrange my work so I can glue multiple things. (or use Bob Smith epoxy and use my calibrated eyeballs).

As for CA, I've had great luck with the black rubberized CA (IC2000 is the name...I think). I use this and thin CA exclusively. It is far less brittle than regular CA and seems to work ok on many plastics. I know people who pretty much use this exclusively for LPR birds. Wouldn't use it in place of epoxy tho.

Another glue that is a little out of the mainstream is Liquid Nails. I've used this off and on for special purpose jobs, quick jobs, and on plastics. Never built a whole rocket with it and it would make UGLY fillets There is a guy in MDRA that has built L3 rocket(s) using only Liquid Nails.

concerning epoxy mixing, has anyone had the chance to use "static mixers"?

These are nipples that you attach to the front of your epoxy glue gun that mixes the epoxy as it dispenses. For very small applications, it can get expensive, but if your doing filets on a HPR bird, it can be quite cost effective because there is no waste and the mix is always perfect, no guess.

i;ll see if I can find a website that supplies these, and post

I thought the large tube dispensers mixed as you squeeze. Still, I use pumps that fit on the West cans. Hmmmm, maybe West sells other dispensers?

you might want to take a look at a polyurethane glue like gorilla glue......much stronger than white and yellow glues, almost as strong as expoxies but no mixing..

https://www.gorillaglue.com


shockie B)

Here is some input from my site:

Elmer's ProBond Polyurethane Glue. It is called "The Ultimate Adhesive", "Bonds Virtually Everything", "Super Strong", "Sand Easily", "Water Proof", and "Stainable/Paintable". The outside cover said that it is the strength of epoxy without the mixing.

In general, I found the glue easy to work with exception for one primary issue. It expands somewhat in volume after being applied. This has not been a problem for attaching centering rings to the motor tube and to the inside of the body. It has been fine for attaching nylon straps to the motor tube and to pistons (if used).

Once dry it appears porous, but it does sand easier than epoxy and I had no primer interactions.

CLICK HERE FOR MORE

-Nick

Nick,

Does the polyurethane glue lose all its volume like the wood and/or white glues do when they cure? I'm thinking of fillets for ttw fin mounting. How flexible is it when it cures? Also, how does it rate for weight as opposed to epoxy and/or the white/yellow glues? It sounds like a great alternative as the more I look at what we do, the more it looks like we tend to overbuild. I have yet to see a joint fail due to glue breakdown. It appears to occur either where the glue adheres to the tube (flexibility?) or below the joint out on the fin, where the glue tends not to be an issue either way.

No, actually, it expands while it cures and stays built up. Look here:

CLICK

This is wet applied on left and fully cured on right.

See more on this subject in this review:

CLICK

It is not flexible when it cures. It is not real brittle either, but does break.

It dries slow and expands all the while. Again, I think the best place for this is internal Bulkheads and centering rings and internal fillets (let it run down the length of the joint) and piston straps.

Here is how I used it on centering rings:

CLICK

I also used it on the Nose Cone and have since lost my nose cone!

- Nick

I originally bought Elmers ProBond to glue together large slabs of 2" foam to make a nosecone core. This was early in my second BAR phase and hadn't had access to may on-line resources. I put on too much, and found the foam would expand enough to lift several large cinderblocks (only about 1/2 inch, but that was still too much!). Lesson: use it sparingly!

As EMRR mentioned, I also used it for centering rings and internal fillets and it seems to have worked fine for that. In a tight space it fills the gap just like foam would. Finally, I used it like foam to hold weight in the end of a large plastic Easter Egg. People complain about glues not adhering to plastic, but after a significant larn dart, this weight was about the only thing left where I put it

My main gripe is the shelf life, once opened, is lousy. The glue reacts with moitsture in the air and doesn't last long.