Fret Leveling Tool DIY

That makes it very hard to maintain the fretboard radius.  I use these.  www.stewmac.com/luthier-tools-and-supplies/tools-by-job/tools-for-sanding/8-radius-blocks.html

They also sell expensive aluminum sanding beams.  I could tape (2) 8" blocks to a piece of 2x4 and do the same thing.  But I find the 8" blocks works fine.  Many times only have sandpaper on 4" of the block and tape on the other end.  Then I can spot sand high spots.  The taped end of the block keeps it from tipping and causing waves in the sanding.  I check the fret level often with a straight edge.