Fin Beveling Jig

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By Mitch Marchi II

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!

GUEST's OPINION:
"11/07 "I have Just used this tip on a few rockets I'm working on. This has to be one of the most ingenious ideas I have seen in a while on this subject. One change I made was to use light aluminum angle for the brace instead of the wooden ones. The angle are washable if glue gets on them and can be used for other things as well. or in conjunction with a fin jig. Grand idea from a great mind." (C.C.N)

1. Fins
   Sand fins to an airfoil shape. Also, sand them so they are thickest at the root, and thinnest at the tip. Again, this will help reduce drag.
2. Fins
   I used a belt sander chucked into my bench vise as a flat bed sander of sorts. Be careful and use proper eye protection when using a belt sander. Always make sure the direction of travel of the belt is away from you which will attempt to pull the fin from your fingertips rather than embed it in your palm. Use double stick tape to stick all similar fins together for sanding as a unit to ensure uniformity. Bevel the leading and trailing edges of the fins using the laminations in the plywood as a guide. Mark where the fins enter the body tube and do not bevel edges below this mark otherwise the gap will have to be filled later on.
3. Fins
   Featured Tip: Fin Beveling Jig - This article describes how I made a fin beveling jig for a standard vibrating floor/surface sander. To build and use this jig, you will need:... more