Jigs to Crown the Fretboard
I use two very simple, shop made jigs to crown my fretboards to a 12" radius. In the beginning I used a Stew-Mac 12" radius block and lot of elbow grease. That was OK but the primary problem was keeping the radius block centered on the tapered fretboard. Quite a bit of material had to be removed and it was difficult to keep the fretboard from moving. As a result I resolved to try to figure out a way to do this tedious job quickly and precisely.
I came up with two simple jigs to do the job.
The first job was to roughly get the fretboard to the 12" radius without a lot of elbow grease. I came up with jig #1. Jig #1 is simply a piece of plywood with a 3/16” strip glued to one side ONLY. Put a strip of sandpaper on the top so the fretboard will not move. Center the fretboard on the jig and send it through your drum sander. It will take material off of one side only. Reverse the fretboard and send it through. Do a little per pass through the thickness sander checking the board with your radius gauge as you go. When it is close to the radius stop.
This jig is designed to keep the fretboard secure and to center the Stew-Mac radiusing block on the fretboard as you sand. Again, it is a very simple jig. Just a piece of plywood with two thin strips of wood (less than the thickness of the fretboard) glued to the plywood at the same taper as your fretboards. You can use the fretboard as a pattern to glue these strips. Lastly, lay the Stew-Mac Radiusing block centered on the fretboard. Now glue a strip of wood on one side that will track the lay of the radiusing block. Once dry, it provides a straight edge which keeps the radiusing block centered on the fretboard. If you did step one correctly, a couple of minutes with the radiusing block by hand will give you a perfect radius with a minimal amount of work.
Note that this works with any radius you wish to use!