Here is another luthier tool,
It's a sanding block designed to sand the radius of a fingerboard.
http://www.labellenote.fr/file/Luthe...13.poignee.jpg
There are lots of different ways to make them, here is my personal approach, it is somewhat similar as 3D printing actually, but with wood :-)
See the article on my site explaining my process :
La Belle Note - Radius sanding block