Beyond glue fillets

[BBowmaster]

I’m starting to move from low-power to mid-power. I’m also trying to make my low-power rockets (mostly exotic space-themed) more professional. Lastly I want my scale models to look clean.

Is Rocketpoxy too much for lpr and mpr fin fillets? Is there a step beyond wood glue or elmer’s I should investigate. The big problem I have with the glues is that they run and shrink.

 

[mjstech]

I'm gonna say overkill. There is titebond wood glue in a thick and quick formula. Then after that, there is hobby style 2 part epoxy...in 5, 6, 15, 30 min times.

 

[Amsterdam]

Titebond makes a trim and molding glue that does shrink like all wood glues but you can lay in on thicker than normal wood glue. It won’t run if applied with care, and allowed to dry probably. I believe laying the rocket flat is the proper way, albeit the most time consuming as you can’t do all the fillets at once

 

[GlenP]

Definitely give the Titebond Quick & Thick a try. You might not want to make one single heavy fillet all at once, but apply a very thin one at first, let it totally dry, then apply more thin layers on top to build it up. Hard to tell how well it turned out, since it dries clear, until you paint it.

 

[Wallace]

I do love Rocketpoxy but it is pretty heavy. If you're looking for something you can "shape" Aeroxopy Light is an epoxy based filler that won't add tons of weight and does have some structural properties. It's not technically an adhesive but if you have things properly attached it'll be your friend..

 

[Murdnunoc]

Theres nothing overkill about epoxy, even in very light and simple things.
Epoxy is very commonly associated with brute strength, but it has many other benefits. It can be mixed with fillers to any viscosity. It can also be applied thick without worry of incomplete cure.
Skip the Rocketpoxy.
Get either Z-poxy or finishing epoxy from the hobby store. They are very thin, but you can mix in microballoons to get a peanut butter or even thicker consistency that makes great fillets that are lighter than any other glue.
Rocketpoxy has fillers to make it thicker, but it's still too thin for fillets. They make up for this with the instruction to let it partially cure till it's thick enough to apply. But that leaves you with a very short working window and a weaker bond. A little silly when you can just make it the right viscosity in the first place and get better results that are very light and sandable.
Good luck and good building!

 

[BBowmaster]

Thanks for all the tips. I’ll try the z-poxy and microballoons first. I’m used to using stuff straight out of the package so I imagine proper mixing will be a bit of a learning curve.

 

[Wallace]

Thanks for all the tips. I’ll try the z-poxy and microballoons first. I’m used to using stuff straight out of the package so I imagine proper mixing will be a bit of a learning curve.

If you're using micro balloons the mix is easy (basically get the mix to desired constancy by adding small increments of filler) and very easy to work with. Strength/toughness will be "probably" good enough.

 

[Wallace]

It will set up quicker though so be ready for that..

 

[Murdnunoc]

Thanks for all the tips. I’ll try the z-poxy and microballoons first. I’m used to using stuff straight out of the package so I imagine proper mixing will be a bit of a learning curve.

See if you can get a hold of some little graduated mixing/medicine cups. The runny epoxy can get tough to dose out evenly.
Like Wallace said, microballoons mix easily. Just don't be surprised when you end up adding a lot. It can triple your volume by the time it mixes up really stiff.
Peanut butter thickness works about right for me and fillets. You can pull up a point with the mixing stick that then slowly falls over.

 

[mjennings]

If you are new to epoxy make sure to minimize skin contact you can develop a bad sensitivity to it. I'll second the Tite-bond quick and thick as well. A kitchen scale is good for epoxy too if the brand you're using has the information available. It's easier to hit a number on a gram scale than eyeballing a measuring cup, some epoxies can be very unforgiving if your ratio is even slightly off.

 

[Murdnunoc]

If you are new to epoxy make sure to minimize skin contact you can develop a bad sensitivity to it. I'll second the Tite-bond quick and thick as well. A kitchen scale is good for epoxy too if the brand you're using has the information available. It's easier to hit a number on a gram scale than eyeballing a measuring cup, some epoxies can be very unforgiving if your ratio is even slightly off.

I do like weighing on a gram scale for small batches.
I did find out, after much time, that my hardener is more dense than my resin! So weighing out the ratio actually yields less hardener than optimal. Now I adjust with 8% more hardener by weight.
If you weigh, check your weights of a known volume.
Epoxy mixes by volume.

 

[Steve Shannon]

When mixing in fillers of any kind, such as microballoons, add the fillers to the separate resin and hardeners first until they are the consistency you want. That way you’re not working against the working time.

 

[afadeev]

Is Rocketpoxy too much for lpr and mpr fin fillets? Is there a step beyond wood glue or elmer’s I should investigate. The big problem I have with the glues is that they run and shrink.

From strength perspective - yes.
From the perspective of sculpting great looking fin fillets - not at all!

All wood glues (Titebond II, etc) are plenty strong for the structural construction of paper/wood airframes and fins. But they shrunk a lot while drying, and thus are a poor choice for creating a cosmetically pleasing convex fin fillet.

I never found anything that creates beautiful, sculptable fin fillets, other than epoxy.
Rocketpoxy may be an overkill, but it certainly fits the bill. So do many other peanut-butter consistency epoxies.

Rocketpoxy has fillers to make it thicker, but it's still too thin for fillets.

That is completely inconsistent with my experience.

Rocketpoxy is fantastic for both strength, and longish cure time that gives you a margin of error of time to sculpt fillets, then go back to fix the mistakes. The latter part is especially helpful for the first dozen times OP will be learning the art of sculpting/"pulling" fillets - it's an acquired skill that takes practice and time.

Get either Z-poxy or finishing epoxy from the hobby store. They are very thin, but you can mix in microballoons to get a peanut butter or even thicker consistency that makes great fillets that are lighter than any other glue.

When mixing in fillers of any kind, such as microballoons, add the fillers to the separate resin and hardeners first until they are the consistency you want. That way you’re not working against the working time.

Adding fillers to epoxies (Z-poxy, or BSI, Great Planes, West system, Proline, MAS, etc) also creates the challenge of getting the mix just right, usually something that is learned by trial and error:
https://www.rocketryforum.com/threads/mixing-ratio-for-microballoons.29778/

Frankly, I would advise OP AGAINST learning both the fin fillet sculpting and filler mixing all in one step.
It's doable, but creates unnecessary complexity, failure, and frustration points.

Rocketpoxy is a great structural and sculptable epoxy.
Learn how to "pull" fin fillets with Rocketpoxy, THEN move onto mixing your own epoxy ingredients to achieve the desired viscosity for your preferred cure-time window.

For instructions, go here:
https://wildmanrocketry.com/pages/downloads

The only way to find out what works best for YOU is by doing.
Good luck!

a

 

[Murdnunoc]

[QUOTE="afadeev, post: 1869171, member: 26986"

That is completely inconsistent with my experience.

Rocketpoxy is fantastic for both strength, and longish cure time that gives you a margin of error of time to sculpt fillets, then go back to fix the mistakes. The latter part is especially helpful for the first dozen times OP will be learning the art of sculpting/"pulling" fillets - it's an acquired skill that takes practice and time.





Adding fillers to epoxies (Z-poxy, or BSI, Great Planes, West system, Proline, MAS, etc) also creates the challenge of getting the mix just right, usually something that is learned by trial and error:
https://www.rocketryforum.com/threads/mixing-ratio-for-microballoons.29778/

Frankly, I would advise OP AGAINST learning both the fin fillet sculpting and filler mixing all in one step.
It's doable, but creates unnecessary complexity, failure, and frustration points.

Rocketpoxy is a great structural and sculptable epoxy.
Learn how to "pull" fin fillets with Rocketpoxy, THEN move onto mixing your own epoxy ingredients to achieve the desired viscosity for your preferred cure-time window.

For instructions, go here:
https://wildmanrocketry.com/pages/downloads

The only way to find out what works best for YOU is by doing.
Good luck!

a[/QUOTE]

You can mix up rocketpoxy and then directly apply to form a fillet?
I've always read you mix it and let it set till it starts to cure and stiffen up.
If that's the case, that tells me the epoxy doesn't have enough filler to use as a fairing compound.
You can get a lighter, more sandable epoxy by mixing in more microballoons to achieve the correct viscosity as soon as it's mixed.
Mixing epoxy isn't that hard.

 

[afadeev]

You can mix up rocketpoxy and then directly apply to form a fillet?

Yes, that's exactly what I do, and it works like a charm.

I've always read you mix it and let it set till it starts to cure and stiffen up.

The reality of the actual application is that it takes time to lay and spread the fin fillets on larger rockets.

I usually crank open RP containers for bigger rockets, with bigger/longer fins. Between mixing the RP, adding and mixing-in the color pigment, then spreading the epoxy into two side-by-side fin galleys of 5-15" long each, I easily burn 5-10 minutes before I am ready to pull the first fin fillet. By that time, the RP is at the perfect viscosity for the job. It also stays readily pliable for another ~10 minutes if I need to go back and fix a mistake, or smooth the transition edge after the tape is pulled off.

Then you have another ~10-15 minutes when you can "massage" fillet's shape with ample application of alcohol (to the fillet, not the user), or remove bubbles with a heat gun, or even scrape everything out, if you just placed the fin backwards (not that THAT ever happened to any of us - don't ask).

If the epoxy was curing any faster than RocketPoxy does, I would be in trouble.

You can get a lighter, more sandable epoxy by mixing in more microballoons to achieve the correct viscosity as soon as it's mixed.

I don't have any data to compare the cured Epoxy weight between different brands, but assume they are all similar. Does anyone know any different?

w.r.t. to being sandable - I don't see that as a consideration.
Once properly pulled, fin fillets are done. You should not be going back to sand anything.

And yes, you can mix your own viscosity with fillers added to thinner epoxies. So far, I had to do that a few times: just for fun, and one time to repair damage on a dinged driveway paving stone (don't ask).

Mixing epoxy isn't that hard.

True.
Then again, hardly anything in this hobby are really "hard", unless we make it so by stacking one level of complexity and uncertainty on top of others.

If the OP has never applied epoxy fillets before, asking him to also learn to mix just the right viscosity of epoxy for the job is an overkill. How would he know what the right viscosity is? Or how much filler is required to achieve it?

It's far simpler to start with a known fin-fillet ready epoxy, like RocketPoxy, and once mastered, move on to mixing your own, if necessary.

IMHO,
a

 

[mjennings]

Has anyone experimented with fillers in other glues? White glue shrinks less than wood glue and could be a place ro start. Maybe mix in some balsa dust .

I know Dr Zooch used "funky glue putty" for some details. FGP was semi dried wood glue.

If you are not trying to derive strength from the fillet you could use a wood filler as well.

Also small triangle stock and a little sanding can make very pretty fillets.

 

[dhbarr]

Dollhouse coping.

 

[Flyfalcons]

You can make excellent fillets with BSI 30-minute epoxy. I find it a bit easier to work with than Rocketpoxy.

 

[lcorinth]

I've made some really pretty fillets on LPR and MPR rockets with just Bob Smith Industries epoxy and microballoons. If you mix enough filler in, it barely adds any weight. They turned out really pretty . The only issue I've had is that at that mixture, it's pretty brittle, and I've come home with some cracked fillets after even really soft landings.

I've switched to Titebond Molding and Trim Glue with an Elmer's cap for LPR rockets, and two or three layers looks pretty good. Makes a small radius round fillet if allowed to dry well between layers. I even use it to fill gaps on larger rockets before laying down epoxy fillets, so I don't get epoxy sinking into the crevices between the fin and the slot. I've recently hear about this Quick and Thick stuff mentioned above, and it sounds pretty intriguing.

 

[OverTheTop]

I would vote for epoxy with microballoons. Relatively easy to sand and much lighter than straight epoxy. Don't use epoxy that too short cure time .

 

[shanejohnson2002]

I'm in the same boat as you. I have successfully used both Titebond Quick/Thick and DAP PlasticWood for fillets on LPRs...and both turn out very nice. I think I like the DAP a little better, because it sands almost exactly like wood. The DAP actually sets up and feels like it adds considerable strength....more than I would expect from a simple fillet.

Now that I'm putting together larger rockets, RocketPoxy is going to be my go-to.

...I've recently hear about this Quick and Thick stuff mentioned above, and it sounds pretty intriguing.

From what I understand, Quick and Thick is just the new brand and label for the Molding and Trim glue. Basically the same stuff.

 

[Wallace]

I've made some really pretty fillets on LPR and MPR rockets with just Bob Smith Industries epoxy and microballoons. If you mix enough filler in, it barely adds any weight. They turned out really pretty . The only issue I've had is that at that mixture, it's pretty brittle, and I've come home with some cracked fillets after even really soft landings.

I've switched to Titebond Molding and Trim Glue with an Elmer's cap for LPR rockets, and two or three layers looks pretty good. Makes a small radius round fillet if allowed to dry well between layers. I even use it to fill gaps on larger rockets before laying down epoxy fillets, so I don't get epoxy sinking into the crevices between the fin and the slot. I've recently hear about this Quick and Thick stuff mentioned above, and it sounds pretty intriguing.

Totally agree, Bob Smith 30 minute and micro balloons make fillets that almost shape themselves. Real easy to form, and smooth to boot. I'd never consider 'em structural though. Way to brittle..

 

[jqavins]

We're still talking LPR and MPR here. As some have noted, Tightbond N is plenty strong enough. For cosmetic fillets (and I've posted this elsewhere a couple of times) I like either DAP or 3M lightweight spackle. It's whipped into a foam, rather like stiff cake frosting. It can be applied and shaped with a finger as easily as with a dowel, and it stays put so you can do all the fillets at once. 24 hours later it's hard enough to sand and soft enough to sand very easily with 320 grit. And it weighs practically nothing. I've used the DAP version extensively (on walls too) and I've relatively recently diacovered the 3M version with primer mixed in; that seems to be working great, but I have not used it as much yet.

 

[dr wogz]

you can also use balsa dust (sand a lot of balsa to get some! ) or baby powder to thicken up your epoxy..

 

[neil_w]

I've recently hear about this Quick and Thick stuff mentioned above, and it sounds pretty intriguing.

It’s the same stuff, just renamed.

 

[lcorinth]

you can also use balsa dust (sand a lot of balsa to get some! ) or baby powder to thicken up your epoxy..

I recently got a ton of balsa dust in one go, when I made my own nose cone.

Didn't know what I might use it for, but it seemed a shame to throw it out.

 

[dr wogz]

I also use balsa dust to remove epoxy from my fingers. Dip, rub, the dust balls up and pulls it off you!