This is the most useful jig I ever done for guitar building. Putting a radius into a fretboard is not only very time consuming, it's one of the most difficult tasks to get right. It requires keeping an even pressure on the sanding block. Not impossible (I've done most guitars with a block) but nerve breaking.
The idea is simple: A frame made out of steel tubing, an adjustable swinging arm mounted on an axis, and a sturdy block that holds the fretboard over a sanding belt (which is another custom machinery I've made out of a treadmill).
I can't stress enough how faster it is than manual sanding, and much more accurate.
This jig was also hosted on homemadetools.net .It won the tool of the week and those awesome dudes even sent me a homemadetools T-shirt back then!