Fillets

[jcb]

Can anyone tell me if they have used 100% silcone caulk for Fillets? This would be used for low powered to mid power only. And for nothing else but cosmetic pourposes. I saw one thread where spackle was used so I thought why not caulk. Any response would be great. Thanks!

[rcktnut]

Can't paint over it!!!!! Harder to work with than most other options!!!

[NjCo]

Paint will not stick to silicone caulk as mentioned above. Also, with a product like silicone, which stays flexible rather than hardening up, you will get dirt and grim building up on your fillets. Almost anything that touches that fillet will stick to it.

I imagine you could use painters caulk though. It wouldn't be any harder to work with that epoxy. It would make a much weaker bond between the fin and body tube than any type of glue. I personally wouldn't do it because of that but I imagine that for most low power applications it might work.

[jpaw33]

Tite bonds molding and trim glue ,grey label,available at any Lowes,is what to use.I've been using this with great results,won't shrink and stays real smooth.It has been recomended many times on this forum. Good luck J.P.

[Micromeister]

Why on earth would anyone use a product that not only can't be painted over but also has no real stiffening ability. Silicone adhesive sealants are made by design to remain flexable.
Fin Fillets are intended to strengthen and streamline the joint. I wouldn't use spackle either but at least that product hardens to a someway rigid mass, that could be painted over.
Personally I prefer 5 or 30minute epoxy fillets, as they add strength to the joint, remain slightly flexable to absorb a little flex on hard landings and can be sanded, polished and/or painted over.

[jcb]

My thought was to use GLUE as I always use then aply a paintable caulk over that to make a nicer fillet. If it is not a good idea then I will scrap that idea. Thanks for the input.

[luke strawwalker]

Use the Titebond Moulding and Trim Glue and it'll turn out beautiful fillets that won't require anything over them but paint to look terrific.

Epoxy makes nice fillets, but it's overkill for model rockets, heavy, and difficult to work with. The Titebond Moulding/Trim Glue makes fillets just as pretty while being water soluable and not requiring gloves, wasted materials, mixing/etc.

Good luck! OL JR

[powderburner]

My thought was to use GLUE as I always use then aply a paintable caulk over that to make a nicer fillet.

That's the right idea.

The glue at the base of the fin is what makes the structural joint. If you don't have a good tight fit of fin-to-BT then adding gobs more glue on the outside of the root is not going to restore the joint quality. In the mean time, excessive amounts of glue can warp the parts (especially model rocket cardboard-type BT materials), can dry into ugly shapes (especially most white glues and some yellow glues, when applied thick), and adds weight at the wrong end of the rocket.

Make a good structural joint and then (if you want) cover with anything you like that works well with your primers and paints. But keep in mind that unless you are super-polishing the entire rest of the airframe (for laminar flow) and airfoiling your fins and polishing them smooth also, and removing the launch lug (or button) and using a tower, then adding fillets is NOT GOING TO DO A DARN THING for streamlining or any practical improvement in performance.

It might look cool, that's a matter of personal choice, but don't fool yourself that fillets are "necessary"