Fiberglass Fillets

[Mao_Zedung]

Hey all! How do you guys do fillets for your fiberglass rockets ? For external fillets I do rocket poxy then smooth out the imperfections with a healthy layer of filler. This being said, I’m getting into fiberglass and filler seems to adhere poorly to phenolic/fiberglass. Was wondering how maintain a smooth finish to your fillets!

 

[David Schwantz]

Any good epoxy will make nice fillets. Some people use tape to outline the fillet. You can use anything to pull them. I have some cut off PVC tubing. But I like using my finger the best. I use a syringe to lay down a bead and then pull it out with finger. If I want a bigger fillet, I use a fatter finger. Very seldom do I need to fill a fillet with bondo. A little sanding to remove the gloss before primer and paint.

 

[Banzai88]

Some pretty good videos on YouTube.

That said, I vary between West Epoxy with filler and 4500. Both work very well and produce smooth, shiny fillets with a single pass.

 

[David_Stack]

This being said, I’m getting into fiberglass and filler seems to adhere poorly to phenolic/fiberglass. Was wondering how maintain a smooth finish to your fillets!

Are you adequately preparing your phenolic/fiberglass surfaces prior to laying down your fiberglass and fillers? Fiberglass surfaces need to be cleaned to remove release films and the like that were the result of manufacturing. In addition it is recommended that the surface be scuffed/sanded to provide a substrate for the epoxy to better adhere to.

Suggested reading: https://www.rocketryforum.com/threa...our-government-doesnt-want-you-to-know.58389/

 

[bjphoenix]

If you really have imperfections to fill you could use auto glazing filler, the red stuff that you might have seen on cars. My dad's shop used the 2-part mix that doesn't shrink. When we had some paint work done in our house our painter used some single part that he would put in the dents on door frames.