Difficulty tuning the middle string on my Cedar Creek dulcimer is driving me crazy, and I'm beginning to think it's due to binding in the nut. Does anyone have any tips for lubricating the nut, I've read a guitar tip that "scribbling" in the groove with a graphite pencil prior to putting a new string in works, but don't really see how to get a pencil into that little space
Alternatively, is it a risky thing to make a few swipes through that slot in the nut with extremely fine grit sandpaper to slightly enlarge the slot?
FYI, the symptom is that when I get the string under tension it no longer raises in pitch smoothly. Sometimes it will stop rising for a partial turn then jump in pitch, most often right when I'm getting close to my target pitch (the string is mocking me, I know it)
. Occasionally the "release" of the binding is significant enough that it makes an audible creak/ping, so I'm pretty certain that's what's going on. Another symptom is that if I get on pitch and then play for a while the middle string slides sharp, which I suspect means that as the string vibrates it helps distribute the tension that was "bound up" between the tuning peg and the nut across the length of the string, resulting in the note going sharp.