Final post of today! - How to make a turn fin. My way anyway...
.063" (1.6 mm) thick 7075-T6 aluminium sheet. Printed out copy of the turnfin to be made, spray glued and attached to the plate.
The center of the holes are punched and the outlines are scribed with a hobby knife (that can be excluded also as you can make it ready with then paper still on the aluminium).
3.5 mm holes are drilled and the two bends are done. Now it can be cut-out. I do it in my band saw and then shape it with a disc sander and the Dremel with a sanding drum...
The disc sander is used to make the sharp edge. Make it almost sharp and make the last bit with a file. Its very easy to go too close to the edge so to speak with the disc sander. I also sand the turnfin with a sanding block and sandpaper making sure all edges are sharp that will be in the water.