Copyright © Thomas Fetter
The fixture simply holds the fin securely in a vertical position, so the disk sander table is tilted to provide the bevel as shown here. I typically use 10 degrees of bevel. A scrap of wood is clamped to the table at 90 degrees to the disk to act as a guide for the fixture.
Medium Fin Sanding Fixture
This shows the disk sander with the table adjusted to a 10 degree tilt
The fin is held in place by a section of 1/8" flat stock that is held in place by two bolts. The flat stock has been tapped for the two bolts. I draw a line on the fin where the bevel should end to act as a guide for sanding
This shows how to calculate where to draw the bevel line by solving for x.
The fixture is then pressed against the sanding disk. Sand a little at a time and check progress. If the bevel is making more progress on one end, just press a little harder on the other end. This will likely happen as the disk will sand more aggressively on the outer side where it is moving faster.
With a little care, the final result is very consistent. I use 80 grit paper on the sander, so final sanding is done by hand using sanding blocks, but all the heavy work has been done by machine!
The same fixture can be used to sand small model rocket sized fins as well. The disk sander would be way to aggressive, so I use a hand sanding block that has been cut at the desired bevel angle. The sanding block rides against the front of the fixture, and the fin is set at the proper height so the sanding block stops when it has sanded to the proper depth (half the fin's thickness at the tip).
The final result for these small basswood fins
I like the look of beveled fins. It's a lot of work to sand the bevel by hand, so this operation is a great candidate for a fixture to be used in conjunction with a stationary power sander. I happen to own a 12 inch Delta disk sander, but this would work well with a stationary belt sander as well. This fixture works for fins roughly up to 6" on a side.
The fixture is very simple. It holds the fin flat against the face plate so the fin can be held at the proper angle and position against the sanding disk.