Do you remember, a few postings back, when I put on the frets but forgot to put in the little marking dots? I had to install the dots between existing frets. They protruded a bit from the fretboard surface. Now I must sand them down level.
The challenge is sanding down the shell dots without sanding a trough in the wood.
the seacret weapon is plain old scotch tape. It is very thin. pretty tough. If you can sand the shell down to the thickness of the tape you have just about solved the problem.
Using a hole punch I cut a hole in the tape just a tiny bit larger than the shell dot.
The tape is put on the fretboard with the hole over the dot.
Now the shell is sanded down to the thickness of the tape and the wood is protected by the tape. It takes just a careful sanding with finer sandpaper on the sanding stick to make it perfectly flat. A MISTAKE CORRECTED !