I've got 3 strings riding too high in the nut causing sharp notes on the first 3 or 4 frets. Don't really want to invest in a professional set of files for this one time need, although the local Harbor Freight sells a couple different sets of cheap needle files. Have no idea about the size/gauge of these files. I understand the string should rest on the nut opposite the headstock side, which requires a slight downhill cut. Any tips on how deep one should cut? A little at a time until the notes ring true? As donepearce has mentioned before, luthiers often leave slots a bit high because they're one stroke away from cutting too deep. What if filing the slots gives me perfect notes but cause an open string buzz.....the action of my guitar is quite low. Raise the bridge and/or adjust relief?