Epoxy for dummies

[Rich Holmes]

Ted, I certainly understand what you're saying. And at the risk of repeating myself, when and if I use up the BSI I'll certainly at least consider Aeropoxy ES6209 or Rocketpoxy or West Systems or something else, and I think it's likely I'll prefer one of them to BSI. I might even do so earlier, if I'm sufficiently fed up with BSI. But for now, until I've got a better picture on how much I'm likely to use epoxy, I'm not about to toss out the ten bucks I already spent on BSI in the name of saving money.

 

[Rocketjunkie]

It took over a gallon of epoxy to build this

 

[Cyril's Scribe]

It took over a gallon of epoxy to build this <img src="https://www.rocketryforum.com/attachment.php?attachmentid=141179"/>

And a gallon of Resin and Hardener West Systems at Fawcett's Marine Supply is only...$232. I wonder how much it would be for Bob Smith? I am glad even my big fiberglassing jobs don't need that much!

 

[JeromeK99]

I think a lot of our epoxy aficionados build a higher ratio of HPR birds, forgetting just how little glue a BT-50 coupler takes!

There is nothing wrong with buying BSI or Pacer epoxies at your local hobby shop. It works just fine for LPR and MPR.

Now if you get into glassing your rockets with heavy cloth, or making tubes and nose cones.. then sure.. that is what the larger quantities are for. They also require fillers to make them better for bonding parts together.

I sometimes glass my LPR birds for strength, to make them last longer in the harsh Southern California desert. I use mostly .75 oz. glass cloth and it doesn't take much epoxy. I mainly use BSI 20min. finishing epoxy. I started going through a few sets in a year during my last building frenzy so I bought some U.S. Composites 3:1 1/2gal+21oz. for around $50 shipped. That is about 10 8oz. sets of BSI for less than half the price. It will probably last me a couple of years!


Jerome

 

[Jmhepworth]

I'm a fan of Aeropoxy. Even though it's thick, it still flows well to make injected internal fillets, and if there is any void between the fin and the coupler, it will flow where you didn't want it. On the other hand, I recently built an Apogee Aspire using wood glue. I had forgotten how easy wood glue is to work with and how much satisfaction there is to having a rocket completely built in less than an hour. For low and medium power rockets, I wouldn't use epoxy at all, unless you are using it to develop skills for high power.

Joe

 

[Onebadhawk]

I'm a fan of Aeropoxy. Even though it's thick, it still flows well to make injected internal fillets, and if there is any void between the fin and the coupler, it will flow where you didn't want it. On the other hand, I recently built an Apogee Aspire using wood glue. I had forgotten how easy wood glue is to work with and how much satisfaction there is to having a rocket completely built in less than an hour. For low and medium power rockets, I wouldn't use epoxy at all, unless you are using it to develop skills for high power.

Joe

+1.

 

[troj]

I'm a fan of Aeropoxy. Even though it's thick, it still flows well to make injected internal fillets, and if there is any void between the fin and the coupler, it will flow where you didn't want it. On the other hand, I recently built an Apogee Aspire using wood glue. I had forgotten how easy wood glue is to work with and how much satisfaction there is to having a rocket completely built in less than an hour. For low and medium power rockets, I wouldn't use epoxy at all, unless you are using it to develop skills for high power.

A lot of high power rockets can be built with wood glue, as well. I love it for its ease of use and easy of cleanup.

-Kevin

 

[Onebadhawk]

I think I remember reading in John Coker's study on adhesives
that on porous paper and unfinished, porous wood
yellow carpenters glue was stronger than epoxy.
Thats amazing ...........

Teddy

 

[Rich Holmes]

Yep. Currently the only things I use epoxy for are (LPR) motor mount and body tube coupler installations. Yellow glue grabs too quick; I've gotten burned by that once too often.

 

[jderimig]

Yep. Currently the only things I use epoxy for are (LPR) motor mount and body tube coupler installations. Yellow glue grabs too quick; I've gotten burned by that once too often.

Just dilute the yellow glue with a little water to give you more working time.

 

[JeromeK99]

Yep. Currently the only things I use epoxy for are (LPR) motor mount and body tube coupler installations. Yellow glue grabs too quick; I've gotten burned by that once too often.

You can solve this by putting a liberal amount on both sides of the bonding surface.

Jerome

 

[Rich Holmes]

You can solve this by putting a liberal amount on both sides of the bonding surface.

Jerome

I tested that (on scrap coupler and BT). Did not work for me. Froze up instantly.

 

[Balsa Bob]

I tried mixing the stuff in advance the night before so I'd have it ready to use the next day... only tried that once, though.

 

[blackbrandt]

I tried mixing the stuff in advance the night before so I'd have it ready to use the next day... only tried that once, though.

:cry:

 

[T-Rex]

I just completed a wood and cardboard 3" upscale of the Estes Citation Starship Vega. 95% of the build was done with Titebond II. Epoxy was only used to secure the recovery harness, an inner tube for the forward fins (which also anchors the recovery harness), the landing leg pads, and the upper portion of the airframe coupler. The epoxy I used was the 1:1 BSI like stuff from Hobby Lobby. It survived its only flight so far just fine.
As was already said, if you are only going to use a little here and there, the 9 oz hobby store / BSI epoxy is fine. If you transition into needing larger quantities, or fiberglass layups, then go after the quart/gallon sizes of the premium product.
Just my opinion.

Oh, and when people say that a liberal amount of yellow glue can be used for MMTs, that means lay a bead in the BT and slam the mount home. Do not spread the glue out, leave it as a bead. Works great every time for me.

 

[Charlee]

Using the correct ratio (yes, with a 10% leeway) and thorough mixing are very important, but the primary cause for incomplete curing is working in too low a temperature. 5 minute epoxy produces enough of it own heat so that this isn't usually an issue, but for the slower curing epoxies the temperature needs to be about 70 degrees F or above during the entire curing time to deliver optimum structural properties. Epoxies love 80 degrees F but above that temperature (which will also give good results) you lose working time.
My favorite mixing surface is a plastic top to a coffee can (or other food product). The lip around the circumference restrains the epoxy and once cured, the epoxy pops right off when the plastic is flexed, leaving a clean surface to use over and over again. Running two parallel equal length beads of the components next to each other gives the correct amount. Make sure the dispensing nozzles of the epoxy bottles are cut at the same spot so that the resin and hardener come out at the same rate.
This method doesn't work well for finishing epoxies like Finish-Cure, which are very thin. A graduated mixing cup or using a gram scale are your best options for these.

 

[BABAR]

Yep. Currently the only things I use epoxy for are (LPR) motor mount and body tube coupler installations. Yellow glue grabs too quick; I've gotten burned by that once too often.

Hmmm. These are usually paper to paper. Any reason plain old white glue wouldn't work? Cheap and does not set as fast as yellow.

 

[Rich Holmes]

Hmmm. These are usually paper to paper. Any reason plain old white glue wouldn't work? Cheap and does not set as fast as yellow.

In the test I did, a thin film of Elmer's Glue-All (the new "stronger formula") froze up immediately. A thick application didn't.

A matter of taste, but my preference is to use a thin application of something I know won't grab rather than a big glob of something that, if you don't use enough, might.

 

[GregGleason]

In the test I did, a thin film of Elmer's Glue-All (the new "stronger formula") froze up immediately. A thick application didn't.

A matter of taste, but my preference is to use a thin application of something I know won't grab rather than a big glob of something that, if you don't use enough, might.

I agree.

The problem in using blobs of wood glue is that you are adding excess weight to accommodate the characteristics of the glue. That problem is compounded for semi-airtight areas like motor mounts because wood glue requires air circulation to cure. No air movement means a long cure time. Which is why you can leave wood glue in the bottle with the cap on and it will still flow a year later. Because epoxy sets by exothermic reaction, it is relatively immune from this problem.

Another thing is that wood glues (perhaps the yellow glues more than the white glues) will tend to draw in the airframe, so you will notice a slight pinch where the MMT rings are.

Greg

 

[JeromeK99]

I agree.

The problem in using blobs of wood glue is that you are adding excess weight to accommodate the characteristics of the glue. That problem is compounded for semi-airtight areas like motor mounts because wood glue requires air circulation to cure. No air movement means a long cure time. Which is why you can leave wood glue in the bottle with the cap on and it will still flow a year later. Because epoxy sets by exothermic reaction, it is relatively immune from this problem.

Another thing is that wood glues (perhaps the yellow glues more than the white glues) will tend to draw in the airframe, so you will notice a slight pinch where the MMT rings are.

Greg

I really don't think weight is much of an issue unless you are building some gigantic rocket... in which case you have a gigantic motor that can lift a bowling ball! Most of the weight in "wood glue" is water that evaporates. Epoxy will retain more weight per volume. Honestly we are talking grams here on a LPR.

Yes, yellow glue shrinks....

I say use the glue that works the best for you! It takes experience to not have that fear of yellow glue grabbing.


Jerome

 

[Phil-AK]

I was in the marine supply store the other day and saw some West Marine emergency repair refill kits. They had two part envelopes with 101 epoxy. Would it work?

 

[4kids49]

I came up through low power, mid power, L1, and L2. Most of the finer points of high end epoxies are overkill for low power. I built my L2 Nike Smoke with 30 min Devcon epoxy that uses dual syringes. It probably was not that accurate. My rocket went past mach 1 to nearly 8000 ft, fell back to the ground on drogue only, and picked up a few scratches. I launched it two more times in the same day. I love Aeropoxy for higher end applications. There are West Systems and Proline epoxies. Yellow glue is very strong for paper / wood applications. I have had issues with motor mounts and wood glue, but I always managed to make them work. I probably sanded the parts so that they slid easily, and once glue was applied, I always kept the part moving when sliding. Once you stop, you can get into trouble. The easiest thing may be to figure out how to make the yellow glue work. When I went to mid power, I used a lot of CA glue. That is real unforgiving. If you want to go with an epoxy, your 30 min. Bob Smith should be fine in terms of cost per use, as you won't need much for your applications.

 

[troj]

I was in the marine supply store the other day and saw some West Marine emergency repair refill kits. They had two part envelopes with 101 epoxy. Would it work?

They'll work; that's typically 5 minute epoxy and it's going to be an expensive way to buy it.

If you only need small amounts of epoxy, you'd be much better off going to the local hobby store and buying bottles of Bob Smith epoxy.

-Kevin