Extreme Air Mail! Mailing Tube Rocket Project!

[rwm]

Interesting. Can you get a smooth hard finish with that epoxy? I have never used it.
Robert

 

[Dhal22]

Interesting. Can you get a smooth hard finish with that epoxy? I have never used it.
Robert

Sure you can. A large percentage of 'painted' model airplanes use an epoxy/fiberglass finish. Paint the Evercoat finish with finishing epoxy, lay your 1/2-3/4 oz cloth over the epoxy, use playing cards to scrape the excess epoxy and let dry. Lighten your next coat of epoxy with talcum powder, let dry and sand smooth. Now you switch to sandable primer, prime and sand, prime and sand. The primer fills any remaining voids. Then paint, then seal with automotive clear coat paint. Clear coat will require sanding as well but use 2000, 3000, 8000 grit sandpaper. After 3 coats of clear you should be at a mirror finish.

 

[Weldo]

So before all these replies about fillers I did some searching around and it seems lots of guys in the R/C airplane world use common lightweight wall spackle on balsa with good results. So I found some drywall joint compound in my basement. I know it's not exactly the same but it must be close right?

I should have known better! There's a lot of water content in joint compound and after I spread a bit on my nose cone the grain raised a lot under the mud. D'oh! Shouldn't have done that. Luckily I wiped/sanded most of it off and after a few hours I was able to sand the raised grain back to normal.

Next time I would fill the holes before the final sanding.

This is great advice! I should have applied filler before removing the dowel so I could do a final sanding of the filler on the lathe. Next time for sure!

For now I think I'm done with body work. There's still a few divots in the wood but they're small and I'm not gonna worry about it. I'm not going for a super nice finish for this project.

 

[Weldo]

Next up is fin making.

I was planning to make them out of 0.080" acrylic since I have some. I'd have to glue them with CA. Not sure if I'll bother with fillets.

Maybe in lieu of fillets I'll try slotting the tube for the fins. I've never done that, even in a kit build.

The idea is to cut a slot in the body tube and make a tenon on the fin that extends through the main body tube and glues to the motor tube, right?

The extra strength of such a configuration should make fillets unnecessary?

 

[rwm]

I am not sold on the acrylic idea. It's heavy and hard to bond. I have some acrylic cement but I don't think it would bond well to cardboard. What about ABS or thin plywood?
Robert

 

[Dhal22]

So before all these replies about fillers I did some searching around and it seems lots of guys in the R/C airplane world use common lightweight wall spackle on balsa with good results. So I found some drywall joint compound in my basement. I know it's not exactly the same but it must be close right?

I should have known better! There's a lot of water content in joint compound and after I spread a bit on my nose cone the grain raised a lot under the mud. D'oh! Shouldn't have done that. Luckily I wiped/sanded most of it off and after a few hours I was able to sand the raised grain back to normal.



This is great advice! I should have applied filler before removing the dowel so I could do a final sanding of the filler on the lathe. Next time for sure!

For now I think I'm done with body work. There's still a few divots in the wood but they're small and I'm not gonna worry about it. I'm not going for a super nice finish for this project.

Sanding sealer help help prevent the water absorption by the balsa. Any balsa filler, spackling, sheetrock mud, etc will work. Even epoxy and milled fiberglass mix............

 

[Weldo]

Sanding sealer help help prevent the water absorption by the balsa. Any balsa filler, spackling, sheetrock mud, etc will work. Even epoxy and milled fiberglass mix............

So I guess you would typically seal the balsa before applying filler. I hadn’t thought of that. Maybe I will try some filler again after I seal/prime.

I am not sold on the acrylic idea. It's heavy and hard to bond. I have some acrylic cement but I don't think it would bond well to cardboard. What about ABS or thin plywood?
Robert

To be honest I’m not sure about it either. I’m assuming CA glue will bond well between acrylic and cardboard, and that’s why I was going to add a tenon. Really I just want to use it because I have it. Probably 1/8” balsa is the right material here, it then I’d have to go to the hobby shop again and spend more money...

I’ll do an experiment and glue a piece of acrylic to the cut off from the tube. See if it holds well enough. Maybe try some different types of glues/epoxies.

 

[Dhal22]

Perhaps G10 sheeting would make good fins. McMaster Carr will hook you there.

 

[Weldo]

I am not sold on the acrylic idea. It's heavy and hard to bond.

Looks like you were right. I tried a small test piece on the cardboard with a water thin CA and it didn’t hold very well at all.

The right thing to do is get some balsa sheet. It’s nice there’s a local shop that carries lots of it. Hopefully I’ll have some time this week to pick some up.

Perhaps G10 sheeting would make good fins.

I don’t know much about G10. It’s a type of plastic, right? But if I’m have to buy something anyway I think I’ll use 1/8” balsa.

 

[Dhal22]

Yes, fiberglass sheeting.