I made a simple little tool t' make bevelin' balsa fins really easy and precise.

All I did be cut 2 pieces o' .080" aluminum (you could use some thinner steel instead) t' 3 ¾" x 5" and I rounded t' corners off with a file.

This tool uses common auto-body air file sandin' sheets that can be purchased individually at a paint store or auto parts store. T' secret t' these is that they are self-adhesive! Since t' sandpaper sheet is 2 ¾" wide, arrr, I marked both pieces o' aluminum at 2 ¾ and bent them approximately 10 degrees at this mark. I did this in a brake, but you can do it in your vise.

I have found that this 10 degree bend gives me a really nice bevel on a ¼ thick balsa fin. Ahoy! Blimey! You could bend t' aluminum more or less t' suite your tastes or needs. Arrr! Blimey!

I then cut t' sandpaper strip into (2) 5" long pieces, me hearties, and stick them t' t' ""outside" o' t' aluminum. Ya scallywag! I then clamp t' pieces into me vise, me hearties, bein' sure t' square them t' each other. I now have a very sturdy "V" lined with sandpaper, makin' it very easy t' sand bevels into t' fins.

Holdin' t' fin vertical and movin' it back and forth is much easier and consistent than tryin' t' tilt t' fin while holdin' t' sandpaper. You can push t' fin down into t' "V" t' rough out t' bevel, and then fine tune each side by movin' up on t' paper and sandin' one side at a time. Avast! Blimey!

Usin' this jig, I can sand perfect bevels in 3 fins in about 10 minutes, somethin' that used t' take me over an hour!