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Old 11-08-2019, 11:34 PM
vulcanitebill vulcanitebill is offline
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Join Date: May 2011
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Default my latest fin fillets

I wanted to relate my experience as a beginner in nicer finishing.

I'm completing a rocket I started a long time ago. This uses a 2.6" Phenolic tube and plywood fins with 29mm motor mount. I extended the fin tabs and attached them to the motor mount, then I slotted the airframe to match and glued the fin can unit inside. I put small epoxy fillets on the outside of the airframe, not intended to be the final pretty fillets.

I've read a lot about how to create good fillets, most of the methods required an epoxy and/or a filler that I didn't have. I didn't want to spend a lot of time and cost hunting down special materials and I wanted to use a method that I could have faith in getting reasonable results from. I had just finished doing a repair of one of the doors of our house with JB Weld epoxy wood putty and had some left so I thought I would try it.

I had already done measurements to determine the fillet radius that I wanted and found a 7/16" socket in my tools that was the right size. I rolled a small snake of the putty, pushed it into the fin root with my fingers, then dragged the end of the socket across the snake from front of the fin to back of the fin. I had to push pretty hard but this squeezed out the excess putty as it went and tooled the shape of the fillet into the epoxy. Once cured the fillets were a good shape but not completely smooth on the surface. I wrapped sandpaper around a smaller socket and used it to sand the putty, then I used some olf Elmers Fill-n-finish to smooth out the surface and then put on many coats of primer. The surface so far looks amazing to me. I'll do a bit of finish sanding with high grit sandpaper and then it will be ready for paint.

I won't say that this method didn't take a lot of time but it wasn't too bad.
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Old 11-09-2019, 06:58 AM
mojo1986's Avatar
mojo1986 mojo1986 is offline
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Join Date: Mar 2005
Location: Kingston, CANADA
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Default

Quote:
Originally Posted by vulcanitebill
I wanted to relate my experience as a beginner in nicer finishing.

I'm completing a rocket I started a long time ago. This uses a 2.6" Phenolic tube and plywood fins with 29mm motor mount. I extended the fin tabs and attached them to the motor mount, then I slotted the airframe to match and glued the fin can unit inside. I put small epoxy fillets on the outside of the airframe, not intended to be the final pretty fillets.

I've read a lot about how to create good fillets, most of the methods required an epoxy and/or a filler that I didn't have. I didn't want to spend a lot of time and cost hunting down special materials and I wanted to use a method that I could have faith in getting reasonable results from. I had just finished doing a repair of one of the doors of our house with JB Weld epoxy wood putty and had some left so I thought I would try it.

I had already done measurements to determine the fillet radius that I wanted and found a 7/16" socket in my tools that was the right size. I rolled a small snake of the putty, pushed it into the fin root with my fingers, then dragged the end of the socket across the snake from front of the fin to back of the fin. I had to push pretty hard but this squeezed out the excess putty as it went and tooled the shape of the fillet into the epoxy. Once cured the fillets were a good shape but not completely smooth on the surface. I wrapped sandpaper around a smaller socket and used it to sand the putty, then I used some olf Elmers Fill-n-finish to smooth out the surface and then put on many coats of primer. The surface so far looks amazing to me. I'll do a bit of finish sanding with high grit sandpaper and then it will be ready for paint.

I won't say that this method didn't take a lot of time but it wasn't too bad.



Interesting approach. Got any pictures?
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