Howdy Gents, For those of you who either make lutes, or adjust your own lutes, I've just found a good tool for working on the grooves in the nut. I had been using the little 4" Swedish craftsman's files, and some on this list have suggested strings coated with an abasive. Tonight I was trying to lower the action on my old guitar and didn't want to go too far. It dawned on me that the "spiral blades" for a scroll saw might work. They do, they are perfect. I've been using them on my scroll saw for a year, but hadn't thought of using them for this (they are relatively new, but available in the US at Sears Hardware - and should be available some where for all of you). It is a round blade with a spiral cutting edge. and using the blade as a "soft file" works perfectly for deepening the "nut slot" gradually (one does have to widen the top of the groove with a small file).
The procedure is to relax a string enough to move it aside. Then take the round saw blade in your fingers and take a few cuts, open the top if necessary, then bring the string back "into battery" and try it. The cut is perfectly round, and easily controllable. It is a slow process, but a safe one. Best, Jon To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
