I made a simple little tool to make beveling balsa fins really easy and precise.

All I did was cut 2 pieces of .080" aluminum (you could use some thinner steel instead) to 3 ¾" x 5" and I rounded the corners off with a file.

This tool uses common auto-body air file sanding sheets that can be purchased individually at a paint store or auto parts store. The secret to these is that they are self-adhesive! Since the sandpaper sheet is 2 ¾" wide, I marked both pieces of 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. You could bend the aluminum more or less to suite your tastes or needs.

I then cut the sandpaper strip into (2) 5" long pieces, and stick them to the ""outside" of the aluminum. I then clamp the pieces into my vise, being sure to square them to each other. I now have a very sturdy "V" lined with sandpaper, making it very easy to sand bevels into the fins.

Holding the fin vertical and moving it back and forth is much easier and consistent than trying to tilt the fin while holding the sandpaper. You can push the fin down into the "V" to rough out the bevel, and then fine tune each side by moving up on the paper and sanding one side at a time.

Using this jig, I can sand perfect bevels in 3 fins in about 10 minutes, something that used to take me over an hour!