Estes Mercury Redstone #1921 Build, Part 5, Fins D

I couldn't see the pencil line at the 1/4" taper width so I set down some masking tape.
I don't always do this. It can help you to not sand over the high point.

The fin rudder squares will be shaped first.
Sand the top knife edge thickness (1mm) first. Just concentrate on the top edge width for now.

You won't get good results by running the fins over a sheet of sandpaper taped to your workbench. Use a sanding block with 220 grit for initial shaping.
Go slow. Sand a few passes and check, sand a few passes on the other side and check.
From the side, right now the taper almost looks rounded.

After the blackened leading edge is the right thickness, then work down to the masking tape at the 1/4" width. Still keep an eye on the black inked leading edge thickness.
Try to flatten the area between the sharp tip and the 1/4" width at the top of the masking tape reference.


Here's the shaped rudder piece.
The inset picture shows two pieces with the ink still on the leading edge.
The two on the right had the ink lightly sanded off with 400 grit.