Applying fins after primer

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AtomicStorm

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Is it possible to apply fins on a regular estes lpr kit after painting with primer? I like to get rid of the spirals with primer and sanding but it takes sooo much longer if the fins are attached and you have to sand in-between and all around. The fins would not be ttw, im sure if they where then it would be ok to put them on after primer but im talking about glueing fins to a primered surface here.
 

rklapp

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I guess that’s one way to do it. I just cover the spirals with CWF and sand the whole tube, glue fins with TB2, fillet with Q&T, then apply primer.
 
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Steve Shannon

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I suspect you already know the answer to your question, but gluing something to a primed tube results in two different weak bonding layers. One is the strength of the primer to tube and the other is the strength of the glue to the primer. Usually that’s not a good thing. Maybe you’ll end up with a combination that’s strong enough, but maybe not. Usually you want the glue to be absorbed into the porous body tube.
But you’re right, it’s easier. 🙂
 

Scott_650

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CFW is Carpenter’s Wood Filler?
Yes.
...but im talking about glueing fins to a primered surface here.
Either mask of the “stripes” where the fins attach or sand the areas clear of primer before you glue on the fins - wrap a small piece of sand paper around something like a Sharpie marker to make a mini sanding block works pretty well. Glueing fins onto a primered surface means you’ll get plenty of practice reattaching them after they pop off on during landing 😉
 

Funkworks

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I like to get rid of the spirals with primer and sanding but it takes sooo much longer if the fins are attached and you have to sand in-between and all around.
At this stage, I found out that finger-spreading Bondo grease, Tamiya putty, or CWF in the spirals works much better than trying to fill them with a primer. Then I sand the grease/putty/filler (without the fins). Then I glue the fins, then I prime. Sanding the primer, even if the fins are in place, is much easier than sanding the grease/putty/filler.
 

Spitfire222

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Just take some sandpaper or files and remove the primer and glassine prior to gluing the fins on. I'll be honest, I find it unusual that most people glue/assemble LPR rockets and then begin finish work. If I'm going to fill and prime the fins and body tube, I do it all when they are still separate. As mentioned, it's much easier to do it that way.
 

neil_w

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Is it possible to apply fins on a regular estes lpr kit after painting with primer? I like to get rid of the spirals with primer and sanding but it takes sooo much longer if the fins are attached and you have to sand in-between and all around. The fins would not be ttw, im sure if they where then it would be ok to put them on after primer but im talking about glueing fins to a primered surface here.
Of course you never want to actually glue to a painted surface. However, contrary to some of the response here, priming the components before assembly is quite common, for exactly the reason you propose. However, we must distinguish between two types of primer: filler/primer, which has a high solids content and for most folks functions *mostly* as a filler, and what I'll call "plain old primer", which functions primarily as a foundation for paint and doesn't really do much filling.

It is filler/primer that would most often be used before assembly, and then sanded mostly off. You can either mask off the areas where the fin roots will go (or other attachment points) or else just sand off those areas. It's no problem. Normally, for spirals, some type of filler (CWF and Bondo are the two most common) would be applied first, because you'd need a *lot* of filler/primer to fully fill spirals (although that's what some folks do).

This is the method that Chris Michielssen uses, as documented extensively on his blog, which I highly recommend you read (http://modelrocketbuilding.blogspot.com/). It works great. For simpler rockets, lately I lean towards just doing the whole rocket at once, after assembly, but that's not practical for more complex designs (impossible to sand).
 

AtomicStorm

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I guess that’s one way to do it. I just cover the spirals with CFW and sand the whole tube, glue fins with TB2, fillet with Q&T, then apply primer.
I got some of the red bondo stuff and it works ok, just alot of extra sanding. I also got some of the 2 part epoxy clay that tim Milligan recommended but it doesnt stick well to estes tubes at all so I'm left with the thick auto primer.
 
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Antares JS

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Cfw? I got some of the red bondo stuff and it works ok, just alot of extra sanding. I also got some of the 2 part epoxy clay that tim Milligan recommended but it doesnt stick well to estes tubes at all so I'm left with the thick auto primer.
CFW = Carpenter's Wood Filler

Epoxy clay has some uses, mostly for gap filling, but TvM really oversells it. It's too thick to be easily used for spiral filling, and I would never use it for anything structural. It can't seep into material and form a really strong bond like liquid can.
 

neil_w

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Epoxy clay has some uses, mostly for gap filling, but TvM really oversells it. It's too thick to be easily used for spiral filling, and I would never use it for anything structural. It can't seep into material and form a really strong bond like liquid can.
+1000
 

AtomicStorm

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The last few rockets ive built, i sprayed a coat of primer then i put the red bondo filler on top of it. That way, i will hit the primer before i sand to deep into the body tube causing fuzzies. Ive also taped the body tube to the end of my impact drill so i can turn the sanding spirals part of the build into a 3 minute job instead of 30 minute or 1 hour tiring job. Saw a guy on youtube do it like this except he does all of the coats (primer, base, clear) and polishes it with steal wool all while spinning the bt on the drill.
 

AtomicStorm

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Glad i got the cheap version of the epoxy clay off of ebay. Weve already used it for shark tooth necklaces and a couple other projects. Great for many little projects, just not rocketry lol
 

prfesser

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I have strengthened the attachment of surface-mount fins by drilling a series of 1/16" holes in the body tube where the root edge will be. Wipe glue into the holes then glue the fin in place over them. Should improve the bond even with primer on part of the surface.
 

neil_w

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The last few rockets ive built, i sprayed a coat of primer then i put the red bondo filler on top of it.
Bondo works well on top of primer; CWF is better applied before hand, although it can still work after.
 

aviserated

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I sand the primer down to paper before supergluing fins on. The thin superglue sets really quick, so fins better be aligned correctly. Be sure to draw lines to be sure. I use JB weld for fillets, very easy to smooth with finger tip.

I have superglued the launch lug on after priming and it is really stuck on there. Scuff primer before gluing.
 

rklapp

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I got some of the red bondo stuff and it works ok, just alot of extra sanding. I also got some of the 2 part epoxy clay that tim Milligan recommended but it doesnt stick well to estes tubes at all so I'm left with the thick auto primer.
You want stuff that somewhat flexible. I find that epoxy easily cracks because it doesn't dry, it cures so only use it on TTW fins. The CWF(!) has some flexibility and is relatively easy to sand. Plastic wood also works well for fillets but haven't tried it yet.
 

icyclops

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Is it possible to apply fins on a regular estes lpr kit after painting with primer? I like to get rid of the spirals with primer and sanding but it takes sooo much longer if the fins are attached and you have to sand in-between and all around. The fins would not be ttw, im sure if they where then it would be ok to put them on after primer but im talking about glueing fins to a primered surface here.
Next time put some thin tape on the fin Lines you drew on the body tube before prime. That way the glue on the root edge of the fin will soak into the paper tube when you are ready to attach them. Then when you apply your fillets the glue should be close to level with the primer....so when you lightly sand the fillets and prime it should be close to the same level.
 

rklapp

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Next time put some thin tape on the fin Lines you drew on the body tube before prime. That way the glue on the root edge of the fin will soak into the paper tube when you are ready to attach them. Then when you apply your fillets the glue should be close to level with the primer....so when you lightly sand the fillets and prime it should be close to the same level.
I did that with the Estes Shuttle main body. I was too impatient to order the Tamiya hobby tape so made my own out of masking tape. Seemed to work fine. Too bad I lost the glider.

B7874D3D-9972-4701-9395-059FE226FCA6.jpeg
IMG_E7032.JPG
 

aviserated

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Gorilla superglue is flexible and takes slightly longer to set.

Hobby lobby sells Estes rockets cheaper than most anywhere. If you screw up you can always buy another to replace it. OR just rebuild it by removing fins and resanding.
 

Nathan

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I tried this long ago on a two stage Estes CC Express. I completely finished painting, then carefully ground the paint off the body tube where the fins attach with a Dremel before glueing on the fins with wood glue. Looked great but most of the eight fins fell off on the first flight.

So my recommendation is to do it the old fashioned way and spend some quality time with sandpaper.

If you want to have nice looking rockets you must transcend space and time until you become one with the sandpaper.
 

afadeev

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I got some of the red bondo stuff and it works ok, just alot of extra sanding.
You can't get away from sanding, no matter what you end up doing with this hobby.
Unless, of course, you don't bother painting at all, and don't care how your rocket looks.

3M Bondo 907 sands way easier than either epoxy or CWF, and dries quicker than both of those. So that's what I use 99% of the time these days.

I also got some of the 2 part epoxy clay that tim Milligan recommended but it doesnt stick well to estes tubes at all so I'm left with the thick auto primer.
TVM's epoxy clay is only good for, and sticks well to, inside of trash cans. It is an absolute crap of a product (there are always better alternatives for every single use case where TVM pitches it). I speak from experience for haven fallen for the sales pitch myself, many years ago, and having junked it.
It must be a pretty high margin product, given how hard he pushes it.

Is it possible to apply fins on a regular estes lpr kit after painting with primer?
As other have correctly stated - absolutely yes!
Just scrub off the areas of the body tube and the fins (you did prep and paint fins as well, right?) where the glue will be applied, and the glued joint will be perfectly strong.
If you want to be a perfectionist, sand off some extra areas around the fin attachment points to leave room for fin fillets as well!

For example (picture below):
- airframe had spirals filled with Bondo 907, sanded, sprayed with sandable primer, sanded. Then areas where fins were going to be glued in were sanded back down to bare paper layer.
- front fins below have been papered, soaked in CA (for extra strength), sanded near smooth, sprayed with sandable primer, sanded (cycles repeated until I got them perfectly smooth).
- aft fins were constructed out of balsa frame and paper skins, then "painted" with epoxy (for serious extra endurance), sanded, etc.

fins and airframe.jpg


Once I attach the last FWD fin, I will move onto applying (epoxy) fin fillets.
Then goes another layer of sandable primer to fill any imperfections (maybe some more Bondo 907, if necessary).
Then paint basecoat (color TBD).
Then paint highlights (colors TBD).

HTH,
a
 
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