Beginner's epoxy question...

[ewomack]

As I start to think about transitioning to HPR, I realize that I have little to no knowledge of what kind of epoxy to use to make larger rockets such as Madcow's Super DX3 or something on that scale.

Is there a good source around for learning the ways of epoxy? Or is it all a lot simpler than my beginner's mind is thinking?

Thanks!

 

[ebruce1361]

There are tons of different kinds of epoxy out there that have their pros and cons to each. If you just want to familiarize yourself with epoxy in general and the characteristics of them, I suggest getting some scraps of wood and plastic and just gluing them together any which way and then try to break the glue joints after curing. A good place to start is with Loctite clear epoxy and JB Weld. Both of these are available at most stores and are pretty affordable. Personally, I like JB Weld for high heat applications like where the ejection charge could do the most damage, but it is heavy. Also, I can vary the consistency of it by mixing it with a bit of acetone to thin it out if the application demands it. Loctite clear epoxy does well anywhere wood glue performs well, but has the added benefit of being able to bond plastic. However, it doesn't grip smooth surfaces very well, so I have to scratch up anything plastic that I glue with it first.

Also, keep in mind the curing time varies from one epoxy to another. Generally, the longer the cure time, the stronger the bond. The shorter cure times are great for tacking fins or parts that don't experience much structural stress, but be aware of heat! Epoxies cure in an exothermic reaction, so the shorter the cure time, the hotter it gets. This can be a problem for vacuumform plastic parts like textured wraps and nosecones.

Anyway, once you try out a few varieties, you'll likely land on a favorite pretty quickly that you are most comfortable with and will have great results. It's really not that much more complicated than regular glue other than the mixing aspect. All you really need for that is a scrap of cardboard and a toothpick (or popsicle stick for larger batches) to mix the parts on. Most epoxies are mixed in an even 50/50 mix, but some of the specialized ones are different. As for the stuff at your hardware store, that should all be easy 50/50 stuff. Some even come with single-use mixing tips that attach to a double-barrel syringe so you don't have to do any mixing; just attach the tip and squeeze it out like cake frosting.

 

[Jim Hinton]

Hey ewomack;

There are various makes and formulae of epoxy, some are pretty simple, others get more involved. The most common error made with epoxy is inadequate mixing. Opaque, colored epoxy such as JB Weld is mixed until a consistent color is observed. I mix the tinted transparent epoxies until they develop a milky appearance. Inadequately mixed epoxy doesn't harden or cure properly.
For a first excursion, I would recommend that you try the Bob Smith epoxy, the 15 minute cure time is a good general use formula. The Bob Smith adhesives are usually sold in hobby shops. Bob Smith offers a deal where the shop's name will be printed on the bottles if they buy an adequate quantity. They offer both CA and epoxy adhesives. The epoxy is the tinted transparent type.
Epoxy does have handling issues, repeated exposure can lead to one developing a sensitivity to the product which you want to avoid. Disposable gloves, mixing sticks, and application brushes are frequently needed with epoxy. I usually mix it on scrap cardboard, but mixing cups are also available.
More advanced epoxy, such as Aeropoxy or West Systems are not based on equal part mixtures and that complicates the issue. Equal parts can be adequately determined by eye. Two to one, three to one, etc is a lot harder to estimate. One usually is required to buy much larger quantities of these types as well.
I hope this helps. Epoxies are a subject that a lot can and has been written about. Most of what you really need to know can be found on the Forum. Denatured alcohol is excellent for thinning and cleanup.

Jim

 

[dr wogz]

Epoxy is usually a 2-part mixture. You either mix by volume (1:1) or by weight (1:1. 5:1, 25:1, etc..)

The more common "hobby" epoxy comes in bottles or a syringe, and you dole out equal parts. BSI is the more common one you'll find at the hobby shop. Another popular brand you'll hear is West Systems, and it's a 5:1 mix ration (1 part hardener to 5 parts resin) And is usually measured out on a small scale. But it comes in a quart.. it'll last a looong time! Other popular choices are Aeropoxy & HYsol. these can be considered 'speciality' epoxies.

The longer the cure time, the more chance the epoxy has to seep into the cracks, crevasses, voids, etc.. to make the bond. (and why epoxy putty is a no-no!)

You can get fillers for epoxy, to make it stiff and stay put where you put it (otherwise it'll run & drip) popular are colloidal silica, faring filler, and some have used balsa dust or baby powder to thicken it. (I like West Systems 407 faring filler for my fillets..)

Wear gloves. Clean up is usually with methyl hydrate / alcohol. ventilate, as some / most will develop an allergy to it at some point. It is also exothermic, so pooling a lot of it will generate heat, enough to melt & deform NCs..

The hobby grade epoxies don't stick to plastic. Others do, but to a varying degree. With that, you can use an old margarine container lid as your mixing surface, then break it off once cured.

I also use Popsicle sticks to mix, but I squrare off one end to get a good mix; scrape the bottom. I also fin it's easier to add to the parts with a square end..

Some consider epoxy overkill for paper & wood construction. a few of us have built 'HPR' with regular yellow carpenter's glue, and they've survived quite well.

Clean well fiberglass parts.

 

[Nytrunner]

There should be some reseources on this in the HPR and Techniques forum

Wear gloves. Exposure to the resins and hardeners can lead to sensitization and allergic reaction with cumulative exposure years later. There are folks that can no longer tolerate the presence of raw epoxy. The period until sensitization is different for different people. Don't take a chance, keep it off your skin. Fresh air or well ventilated area is highly recommended.

A rule of thumb is the longer the cure time, the stronger the bond. That being said, I only used Loctite 5-min HD epoxy from home depot on my L1 rocket, and it's help up nicely.
If you're laminating fiber fabrics onto tubes or laying up composite tubes, you want to use a thin laminating epoxy. For bonding structural components, you'll use either a thicker structural epoxy, or add thickeners to a thin epoxy.

For the wood/cardboard type rockets, titebond II woodglue is plenty strong. It's designed to bond wood fibers after all, and paper tubes are highly refined wood product
Both wood glue and epoxy will be stronger than the materials they're bonding together (fins will break, tubes will delaminate).
You should use epoxy for anything contacting composite materials, plastic, or metal. JB weld is recommend for metal retainers on the motor mount (the original steel weld, not the

 

[Steve Shannon]

As I start to think about transitioning to HPR, I realize that I have little to no knowledge of what kind of epoxy to use to make larger rockets such as Madcow's Super DX3 or something on that scale.

Is there a good source around for learning the ways of epoxy? Or is it all a lot simpler than my beginner's mind is thinking?

Thanks!

No matter what epoxy you end up using, get the West Systems User Manual and study it:

https://www.westsystem.com/instruction-manuals/

 

[BMcD]

John Coker made a video on types of epoxy that is informative.

 

[ebruce1361]

You should use epoxy for anything contacting composite materials, plastic, or metal. JB weld is recommend for metal retainers on the motor mount (the original steel weld, not the

Not the...Not the WHAT?

GAAAH! I absolutely HATE cliffhangers! Will he finish the sentence? Find out in the next exciting episode!

 

[Steve Shannon]

Not the...Not the WHAT?

GAAAH! I absolutely HATE cliffhangers! Will he finish the sentence? Find out in the next exciting episode!

There are two kinds of people, those who can extrapolate…

 

[Nytrunner]

Not the...Not the WHAT?

GAAAH! I absolutely HATE cliffhangers! Will he finish the sentence? Find out in the next exciting episode!

Oop, I had to go back to real work at that point.

The original steel weld is what you want, not the other JB products like water tight, plastic weld, JB Qwik, etc.....

(I had to try real hard not to cut off the sentence again and say Oh NO! Coronavirus has got me!)

 

[AfterBurners]

Another option would be "Fix It" epoxy clay. It's easy to use and not as messy. It allows you a 3 hours windows and you can do all the fillets at once. It doesn't stink, put off bad fumes or make a mess. You should check it out. It's as easy as playing with play doh.

 

[ebruce1361]

Another option would be "Fix It" epoxy clay. It's easy to use and not as messy. It allows you a 3 hours windows and you can do all the fillets at once. It doesn't stink, put off bad fumes or make a mess. You should check it out. It's as easy as playing with play doh.

The fixit clay (sold in sticks, you just cut off a chunk of what you need, and knead it to mix) as well as the epoxy putty/paste (like PC-7) are great for fillets or shaping pieces (I've seen fin pods and scifi spaceship gun barrels sculpted from the stuff), but aren't well suited for actually attaching one thing to another because it won't flow into the material to create a solid bond. Also, when it comes to fin fillets, a little bit of the clay or putty epoxy goes a long way. Roll skinny snakes of it to pack into the joint and spread it smooth and you'll find quite a bit is left over. I know, I tried fillets for the first time some fifteen years ago with some PC-7 on an Estes Stormcaster and ended up with globs 3/4 in wide. Yeah, it can be sanded, but that was a ridiculous amount. I could have done fillets for three more rockets for how much I put on there. But then again, the world will come to an end before those fins ever snap off!

 

[AfterBurners]

You live and learn. Also with the clay I still outline fillets with tape and make them as uniform as possible. Using denatured alcohol to smooth them and get rid of the "edge" when you pull the tape back. If you make the fillets and you are building rocket that's not card board you can get pretty aggressive with sanding the fillets. I start with 150 and work my way down. That's the advantage of not building card board. No spirals to fill and you can sand with almost any grit paper.

 

[John Taylor]

+1 on Bob Smith. Readily available and works great for most applications.

 

[GlenP]

For the MPR Estes PSII E2X models, like the Majestic, E and F 29mm black powder powered, maybe 29mm composite F or G power, for plastic fin to cardboard and plastic centering ring and engine retainer to cardboard engine mounts and body tubes, is there any suitable alternative to Epoxy for those plastic to cardboard joints?

 

[BABAR]

There are two kinds of people, those who can extrapolate…

There are three types of engineers, those who can count and those who can’t.

 

[ThreeJsDad]

As I start to think about transitioning to HPR, I realize that I have little to no knowledge of what kind of epoxy to use to make larger rockets such as Madcow's Super DX3 or something on that scale.

Is there a good source around for learning the ways of epoxy? Or is it all a lot simpler than my beginner's mind is thinking?

Thanks!

I wish !!!! I have been working with Epoxy and Epoxy based resins for over 20 years and much of that time I have been doing in professionally. I have had my own shop doing composite work and I worked in an Aerospace R&D shop. When I started out there was very little in any information that was easily accessible. I learned a lot through filling garbage cans, maybe we can save you that step.

There are a few "basic" rules to understand with epoxy and epoxy based resins.

The faster they cure the hotter they get as they cure. They all exo-therm but I have used some that will burn if you get some on your gloved finger. Slower curing epoxies give off less heat and are normally less brittle when cured. This is important to those building HPR's because of the stresses the rockets endure during launch.

Thickening agents such as micro balloons, flour, or Cabosil accelerate curing which causes more heat. I mention heat again because it can be enough to deform a nose cone. If you are filling the tip of a nose cone put it in a bucket of ice.

Most good epoxies have a very long shelf life but they do not respond well to thermal cycling. Once mixed you have what ever working time your resin allows.

Post curing in a hot box or curing oven always helps. This is for after the initial cure is done.

Even a 30 minute epoxy is not up to full strength for at least 24hrs. I have used lay-up resin that was "cured" in my hot box for 24 hrs and was basically done but would not reach full hardness for another 7 days.

Latex clothes will not stop the chemicals that cause the allergic issues. I now have a bad allergy to epoxy because I did not know this 15 years ago. Now if epoxy gets on my hands I have to pour water that is close to boiling to stop the itching. Nitrile gloves are the key here.

The key to working with epoxies is prep. make sure EVERYTHING is laid out and ready. I suggest you even move through the motions of the process just to make sure you are not putting something where it can get bumped, knocked over or contaminated.

If you are doing a decent sized mix, pour it out on a paper or foam plate. This will give you more working time because it will slow the cure. Leaving it in the cup accelerates the cure. I had a buddy skip this step and melt a plastic cup because the epoxy got so hot sitting in the cup while he worked on something.

For most of us the 30 minute Epoxy from Hobby Lobby works great. If you want to get into fiberglassing tubes and fins or even rolling your own tubes get in touch with me as there are some more tricks I can share. If you looking for a serious Epoxy and want to step things up take a look at Resin Research. Their resins as as good as any and better than most. They even have a hardener that is comparable to hobby epoxy for curing time but the mechanical values surpass anything we can find in a hobby shop.

Oh, the BIG TIP...Vinegar will clean up un-cured epoxy.

 

[ThreeJsDad]

For the MPR Estes PSII E2X models, like the Majestic, E and F 29mm black powder powered, maybe 29mm composite F or G power, for plastic fin to cardboard and plastic centering ring and engine retainer to cardboard engine mounts and body tubes, is there any suitable alternative to Epoxy for those plastic to cardboard joints?

Not really. If it was wood and cardboard you could use wood glue but for gluing two different materials epoxy is tough to beat. Now that I think about it, you could try the non-foaming Gorilla glue. Their CA is the best I have used.

 

[ThreeJsDad]

Epoxy is usually a 2-part mixture. You either mix by volume (1:1) or by weight (1:1. 5:1, 25:1, etc..)

The more common "hobby" epoxy comes in bottles or a syringe, and you dole out equal parts. BSI is the more common one you'll find at the hobby shop. Another popular brand you'll hear is West Systems, and it's a 5:1 mix ration (1 part hardener to 5 parts resin) And is usually measured out on a small scale. But it comes in a quart.. it'll last a looong time! Other popular choices are Aeropoxy & HYsol. these can be considered 'speciality' epoxies.

The longer the cure time, the more chance the epoxy has to seep into the cracks, crevasses, voids, etc.. to make the bond. (and why epoxy putty is a no-no!)

You can get fillers for epoxy, to make it stiff and stay put where you put it (otherwise it'll run & drip) popular are colloidal silica, faring filler, and some have used balsa dust or baby powder to thicken it. (I like West Systems 407 faring filler for my fillets..)

Wear gloves. Clean up is usually with methyl hydrate / alcohol. ventilate, as some / most will develop an allergy to it at some point. It is also exothermic, so pooling a lot of it will generate heat, enough to melt & deform NCs..

The hobby grade epoxies don't stick to plastic. Others do, but to a varying degree. With that, you can use an old margarine container lid as your mixing surface, then break it off once cured.

I also use Popsicle sticks to mix, but I squrare off one end to get a good mix; scrape the bottom. I also fin it's easier to add to the parts with a square end..

Some consider epoxy overkill for paper & wood construction. a few of us have built 'HPR' with regular yellow carpenter's glue, and they've survived quite well.

Clean well fiberglass parts.

I used Baby Powder as thickener for some molds once. They did smell nice when it came time to polish them.....

I agree with wood glue for paper and wood construction. In some cases I think it hold better than epoxy.

 

[ewomack]

All I can say is wow. Everytime I ask a question here I get more than plenty of extremely helpful responses and information. This thread has shown me the true complexity of epoxy. I have a lot to process and think about. I do like the recommendation of "practicing" so I don't mess up an actual rocket kit (especially a higher cost HPR one), so I may try something out and see how it goes.

I'm planning on ordering a MadCow Super DX3 to fly for certifications and some fly-highing electronics experiments. It sounds like one can get away with using wood glue on this kit as long as the plan is to stay under I engines, but for engines of higher power, from what I've read, epoxy is probably required. I'm hoping to use this rocket as a HPR experiment so, assuming all goes well, I would like to fly it beyond the wood glue threshold. So, epoxy it is.

 

[Nytrunner]

It sounds like one can get away with using wood glue on this kit as long as the plan is to stay under I engines, but for engines of higher power, from what I've read, epoxy is probably required.

Darn i must have missed the "under I" memo when i flew this K750

Jokes aside, its the thrust and speed of the flight more than the power of the motor thats the issue. A wood glued 4" rocket with a 38mm mount can take most anything except "maybe" the hardest hitting Warp-9 or V-max motors. Cuz you can butt the thrust ring and centering ring up against the fin tabs.

Flutter and coupler steength becomes rhe weakness

 

[Speaknoevil]

View attachment 408487

Is that an Exocet?

 

[Nytrunner]

Is that an Exocet?

Sport scale tomahawk CM. L2 from my sig vv

 

[Speaknoevil]

Sport scale tomahawk CM. L2 from my sig vv

Cool, thanks.

 

[ewomack]

Darn i must have missed the "under I" memo when i flew this K750

Jokes aside, its the thrust and speed of the flight more than the power of the motor thats the issue. A wood glued 4" rocket with a 38mm mount can take most anything except "maybe" the hardest hitting Warp-9 or V-max motors. Cuz you can butt the thrust ring and centering ring up against the fin tabs.

Flutter and coupler steength becomes rhe weakness

View attachment 408487

Thank you! That's one reason that I'm posting things that I read (and maybe misunderstand), because my head is spinning over this new vast landscape of epoxy. To make sure I understood what you just posted, does that mean that I could build a DX-3 with wood glue and, as long as I don't exceed certain thrust levels, still fly it with J engines? If so, I'm a happy hedgehog because my space is limited for building, not to mention my well-ventilated space. To top it off, I live with a bird who has a fragile respiratory system, so anything high chemical and stinky could cause him nasty lung damage. But wood glue is perfectly fine to use indoors even with the bird.

 

[Nytrunner]

To make sure I understood what you just posted, does that mean that I could build a DX-3 with wood glue and, as long as I don't exceed certain thrust levels, still fly it with J engines?

Yes, mainly because of the great variety of J motors. You can reach great altitudes with a Long burning J that doesnt put a ton of stress on the airframe. Or you may shred it on the H999 or I1299.

Using openrocket or thrustcurve you can see the max velocity you'll reach. The clipped triangle fins on the DX3 are a very strong shape: long root, small tip, but still good working area in the airstream.

Start with H's move up in power/strength of motor as you get comfortable and observe how it performs.

If you want a data point, that tomahawk has flown 500 mph (so far).

 

[bmonagle]

After 45 years of building model airplanes and rockets with wood glue, CA and epoxies, there was no question that I would build my first HP rocket, a Super DX3, with epoxy. Straight Bob Smith 30 minute epoxy for actual joints and filled with microballoons for all fillets. I used single deploy motor ejection on my Level 1 cert (H180) and dual deploy electronic with motor backup for my Level 2 cert (J350). The picture is the same rocket on its 20th high power flight. These days there are very few cases where I would use 5 minute epoxy. In my experience, it never sets nearly as hard or strong as the longer setting formulas.

I have never noticed much of an odor from epoxies, but then again my wife says I can't smell anything.

The only thing I regret about building this rocket is that I used a Madcow motor retainer instead of an Aero Pack (trying to save $17)

Blair

 

[jlabrasca]

is there any suitable alternative to Epoxy for those plastic to cardboard joints?

I've used Elmers ProBond Advanced or Loctite Go2 for attaching Estes 24mm and 29mm screw on retainers. Both seem to work. When I had a forward closure failure on my 40-120 casing -- blowing the motor out the back of the rocket -- the plastic retainer cap failed before the ProBond glue joint.

 

[ewomack]

Madcow's Super DX3 instructions refer to "5 minute epoxy" in the "you'll need these items to complete this kit" section. It sounds like some people have gone this route, while others have gone the 30 minute route and still others have used simple wood glue to make this HPR kit.

I'm now leaning towards using epoxy because I'm hoping (hopefully not in vain) to get a lot of flight time out of this rocket. I want to keep my number of HPR giant rockets to a minimum, so I want to optimize each one's performance. Given that, it sounds like epoxy is probably the safest bet.

Thanks everyone for the excellent responses and discussion in this thread. I've definitely learned that this topic could probably serve as a doctoral engineering thesis... and it probably has! But I'm still overall confused by the variety and complexity of epoxy. But it doesn't sound like I'm the only one.

 

[Jim Hinton]

Madcow's Super DX3 instructions refer to "5 minute epoxy" in the "you'll need these items to complete this kit" section. It sounds like some people have gone this route, while others have gone the 30 minute route and still others have used simple wood glue to make this HPR kit.

I'm now leaning towards using epoxy because I'm hoping (hopefully not in vain) to get a lot of flight time out of this rocket. I want to keep my number of HPR giant rockets to a minimum, so I want to optimize each one's performance. Given that, it sounds like epoxy is probably the safest bet.

Thanks everyone for the excellent responses and discussion in this thread. I've definitely learned that this topic could probably serve as a doctoral engineering thesis... and it probably has! But I'm still overall confused by the variety and complexity of epoxy. But it doesn't sound like I'm the only one.

Hi ewomack;
Five minute will probably get it done, but that isn't much work time. I generally don't use anything faster than 15 minute.

Jim