I've posted this before, but unfortunately I could not find the link. It's a very simple fin sanding jig that has produced excellent results on fins from 3/16 up to .3". (Of course you need a jig for each fin thickness.) The design is easy to reproduce- simply create a rectangle and subtract the triangle that forms the interior (with 15º sides or whatever angle you want). Subtract a rectangle just slightly larger than the fin thickness (I do some very small test prints to find the right value. Then subtract cylinders to form the screw holes. I use wet/dry sandpaper and started with 80 grit and then worked up to 220. I wet sand in a big utility sink to help eliminate any dust.
Of course you need to have a 3D printer or know someone that does.
A word of warning though, you can create a leading edge that is sharp enough to cut, which I learned the hard way - at least twice!
Tony
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