Fillet question - is epoxy necessary on outside Fin-BT for G,H?

[Mike Helm]

When I was building and flying low power I observed that wood glues would shrink and sometimes pull the fins out of alignment due to shrinkage. This shrinkage also caused some dimpling in the fillets. I started using slow cure epoxy and never looked back. 30 minute is fairly common but you can sometimes find 45 minute which is even better. The longer cure times allow the epoxy to better wet and penetrate with the added benefit of self leveling for very smooth and consistent fillets. Just make sure your rocket is level and let gravity do its thing. Use a finger dipped in alcohol to remove any excess. You will save time and weight in the long run.

 

[Weldo]

I finally picked up some Titebond Quick and Thick. It does indeed make a nice fillet! It goes on smoothly and it's got a nice silky texture that makes a very nice even fillet. It does loose some volume upon drying but not as much as regular yellow glue.

I've used Titebond III for fillets before but it shrinks so much when it dries that it will sometimes leave tiny gaps and voids in a fillet that looked perfect when wet. Quick and Thick is definitely better in that regard.

 

[rharshberger]

Is that all you use it for? I guess there's no reason to use it over regular wood glue for general assembly?

The reason not to use TB Q&T for general assembly is that TB, TBII, TBIII penetrated the wood and paper better providing a stronger bond. TB Q&T will bond the two materials, but the thinner glues are better, I use TBII (its what I use in my shop) for all initial bonds on cardboard and wood rockets even the first layer of fin fillet is usually TBII, then I start building my fillets with Q&T on top of that.

 

[Weldo]

Makes sense.

 

[MoreCowbell]

Interesting thread, and timely for me. I have flown only HP for many years, but am in the midst of a trip down memory lane. The first model rocket I built back in 1972 was an Estes Astron Sprint. I have always had a soft spot for that kit. Anyhow, I bought and am building the Astron Sprint XL, and I am about at the point to attach fins and create fillets. Having built dozens of Estes kits in the distant past, I am well familiar with the "shrinking fin fillet" when using wood glue, and this thread has helped me decide that I will attach the fins with 5-minute epoxy, then fillets with 30-minute epoxy and microballoons.

 

[AfterBurners]

Was watching the Zephyr build video, will be starting that build in a week or so. Tim puts epoxy fillets on the outside fin -> BT.

For my 29mm builds I epoxy the inside parts (CR-MT, Fin-MT, CR-BT) but use wood glue fillets on the outside Fin-BT joint. Basically just faster, less messy, easier.

Is there that much stress on TTW fins for G,H motors that epoxy fillets are necessary on the outside BT-Fin?

No it's not necessary. Since the rocket is wood and card board you are better off using wood glue. Two reasons it is stronger than the materials itself and it will save you weight plus it's non toxic. What you bedd to know us epoxy is most commonly used when bonding non like materials. E Tyrone on here overbuolds their rockets. Don't follow their build techniques including TVM. They're complete idiots!!

 

[Alan R]

No it's not necessary. Since the rocket is wood and card board you are better off using wood glue. Two reasons it is stronger than the materials itself and it will save you weight plus it's non toxic. What you bedd to know us epoxy is most commonly used when bonding non like materials. E Tyrone on here overbuolds their rockets. Don't follow their build techniques including TVM. They're complete idiots!!

Those were my thoughts. I know what glue works on different materials. It's just the instructions call for epoxy everywhere on this rocket (my first HPR) and so I was specifically asking the question regarding fillets. I don't believe they need epoxy.
Rocket is completed now with Titebond fillets, just waiting for a paint job btw.

 

[heada]

Epoxy will work but it's way overkill. Wood glue is ideal for gluing wood like substances (plywood and paper) together. Sand or score the paper, sand the plywood to rough it up, use wood glue. If all you have is epoxy, you can use that but it's not required.

 

[ChicagoDave]

I'm doing a build thread on a LOC 2.26" Sandhawk. I'm using mostly wood glue (I will use epoxy for some applications). I have some photos of how I prepare the body tube for wood glue application. https://www.rocketryforum.com/threads/loc-sandhawk-2-26-build-thread.159170/

In my experience the wood glue fillets perform as well as or eve better than epoxy on the plywood to cardboard joint. In either case the failure point is always the cardboard delamination, so the more contact area you can get with the cardboard the better.

 

[Alan R]

Epoxy will work but it's way overkill. Wood glue is ideal for gluing wood like substances (plywood and paper) together.

I believe, from my own personal experience and research, that for midpower stuff epoxy should be used for motor mounts, and for fin attachment (TTW) to the MMT. The rest - not much else really, Titebond is fine. And Titebond would actually work for all the motor mount things because it just plywood and cardboard. Epoxy is just for peace of mind.

 

[neil_w]

I'll try some Q&T for fillets for sure! I like one part stuff! Lately I've been using Titebond Polyurethane to coat my balsa fins in a fin press. It works pretty well. Makes a nice flat, hard and smooth surface with no epoxy to mix.

Good opportunity to put in a plug for my Q&T Fillets thread: https://www.rocketryforum.com/threads/doing-fillets-with-titebond-quick-and-thick.148632/

In general, because the Q&T is so... well, "T", it won't soak into joints the way regular TB will. So I have adopted the habit of doing one small, quick-drying fillet with TBII, and then using Q&T on top of it for the additional cosmetics.

I will also echo the benefit of removing or at least scuffing the glassine layer. These days I mostly just sand the area to scuff it up, and it soaks up the glue nicely.

 

[AfterBurners]

Those were my thoughts. I know what glue works on different materials. It's just the instructions call for epoxy everywhere on this rocket (my first HPR) and so I was specifically asking the question regarding fillets. I don't believe they need epoxy.
Rocket is completed now with Titebond fillets, just waiting for a paint job btw.

Not sure if the kit has a coupler but epoxy works best for mounting the motor mount within the airframe and the airframe coupler. Wood glue will almost always lock up on you unless you are quick about it.

 

[Weldo]

For you guys using Titebond II, does it dry faster than Titebond III? I've been using TBIII since I had some around but I'm almost at the point of needing to resupply. When I started building rockets I liked that TBIII was the strongest wood glue option, but now I'd surely trade some strength for quick drying. As others have said the cardboard tube will de-lam long before the glue fails in any case.

 

[neil_w]

I haven't used TBIII, but according to this chart: yes.

 

[HVArcas]

Parchment paper works great. Epoxies of all types and even CA peel right off... It is my go-to non stick for building.

Same, using west 105 and jbweld here

 

[Weldo]

Thanks @neil_w! TBII it is!

And I also have taken to using parchment paper. Truly nothing sticks to it! I have noticed though that after it gets wet with glue, the glue will peal right off when it's cured but the parchment I was using took on some waviness and wrinkles, so reusing it multiple times may not be possible if a smooth surface is required. Luckily it comes in a big roll!

 

[HVArcas]

I believe, from my own personal experience and research, that for midpower stuff epoxy should be used for motor mounts, and for fin attachment (TTW) to the MMT. The rest - not much else really, Titebond is fine. And Titebond would actually work for all the motor mount things because it just plywood and cardboard. Epoxy is just for peace of mind.

Flew K740s on a woodglue-exclusive 4 inch rocket, works great. Motor mount, fin attachment, whatever.

 

[Alan R]

And I also have taken to using parchment paper.

Oh another tip.. I use plastic oj jugs for my epoxy mixing. It has all these nice little "trays" built in. The epoxy "kinda" sticks, but you can bend the plastic and the dried epoxy can be peeled off if you want to reuse a section.

 

[jqavins]

Parchment paper works great. Epoxies of all types and even CA peel right off... It is my go-to non stick for building.

I don't know about West or some other epoxies, but for JB, PC7, various clay epoxies, wood and white glues, and CA wax paper works to. I have both in my drawer in the kitchen, and usually reach for the wax paper because it's a little cheaper (I think). Never had any trouble.

 

[HVArcas]

I haven't used TBIII, but according to this chart: yes.
View attachment 415108

is original/premium/ultimate same as 1/2/3 ?

 

[CalebJ]

Yes, respectively.

 

[Nytrunner]

I liked that TBIII was the strongest wood glue option, but now I'd surely trade some strength for quick drying.

What others have said about TBII locking couplers in place is true. I rely on quickness and occasionally a guide to get them into place before it locks up, but have had some close calls.
May want to keep a small bottle of TBIII around for motor mounts/couplers when you 1st start using TBII

 

[mbeels]

What others have said about TBII locking couplers in place is true. I rely on quickness and occasionally a guide to get them into place before it locks up, but have had some close calls.
May want to keep a small bottle of TBIII around for motor mounts/couplers when you 1st start using TBII

I use white glue (Elmer's Glue All) for couplers, it is still plenty strong for cardboard builds (especially couplers with all that surface area). The white is much easier than wood glue for sliding in and positioning a coupler.

 

[neil_w]

Glue All definitely is better than wood glue for couplers and such. Epoxy is better still if you need a bit of time to adjust positioning.

 

[Weldo]

I don't know about West or some other epoxies, but for JB, PC7, various clay epoxies, wood and white glues, and CA wax paper works to. I have both in my drawer in the kitchen, and usually reach for the wax paper because it's a little cheaper (I think). Never had any trouble.

Awhile ago I dabbled in balsa airplanes, like this one:

and when I glued up the wing framework I had them laying flat on a sheet of wax paper. I used some thin CA and I did experience some wax paper sticking to the balsa. I probably over applied the glue in those areas, but it did stick sometimes. I think the brand I had was Cut-Rite.

 

[Mugs914]

I build balsa airplanes too Weldo. In fact, I often found myself cutting parts off of a piece of wax paper after gluing them together with CA. I had a friend recommend parchment paper and I've never looked back.

Just finished this one up, BTW:

 

[Alan R]

Just finished this one up, BTW:

That's mighty pretty.

I've never had any luck with airplanes. I remember trying to build one of those balsa planes when I was a kid. I didn't have the patience for it back then. I thought it might be fun to attempt another. I built this one from instructions on youtube at the start of the lockdown with balsa sticks and CA, but it doesn't glide very well. I dont have any giant rubber bands to test it with the prop. It's also very fragile. CA didn't really glue the balsa well.

 

[CalebJ]

I bought a couple of balsa kits at the beginning of this mess. They're sitting on my build pile to hit soon. Hopefully I won't screw them up too badly.

 

[Alan R]

I bought a couple of balsa kits at the beginning of this mess. They're sitting on my build pile to hit soon. Hopefully I won't screw them up too badly.

I can design a rocket that will fly. I can build a rocket that will fly. I can even screw-up while building the rocket and it will still fly.
Airplanes... if you screw up ANYTHING they don't fly. They require much more finesse.

 

[CalebJ]

That's what I'm afraid of! With a little luck they'll at least look decent. It's the Guillow Javelin and P-51 kit - both look reasonable to construct and were cheap enough that I won't lose a ton of sleep if there's a miserable failure involved.

The one I'm really afraid to screw up is a plastic model of a Lear 23. I bought that after my grandfather passed - it was the plane he flew towards the end of his career and the only one I have any memory of (I was 5 when he retired). I had enough trouble finding that several years ago, it's long out of production. Probably even harder to locate now if I need a replacement.