Hi guys

I've got a guitar that was setup for heavier strings than the ones I'm using now. I've setup the guitar for these lighter strings myself so the action is great, but there are some tuning issues. I'm wondering if it could be the nut that's filed for larger strings? Can the nut be filed again for the lighter strings? Or do I have to buy a new nut every time I change to lighter strings?
errmmm i remember somewhere hearing someone (i believe it was paul gilbert) say that you shave bits of graphite of the end of a pencil into the nut as to fill it out slightly again i dont know if that helps or not though =/
I went from .42 to .56 (adjusted the truss rod, lowered the action), and i didnt need to do something to the nut
It stayes on tuning everytime