How To Check Nut Slot Depth
If the buzzing sounds like it's coming from the 1st fret side, I suppose that your correct about nut slot depth being too deep. I've got one guitar that has that problem. I haven't gotten around to fixing it yet, but it buzzes when the the action is the way I like it and it's no fun to play when I raise the action.
Action and a badly shaped nut: That’s the situation with the nut on this old May Bell guitar. Dan Erlewine lowers the nut slots wh. If backlash is more than.012', loosen right-side adjusting nut one slot and tighten the left-side adjusting nut one slot. If backlash is less than.003', loosen left-side adjusting nut one slot and tighten the right-side adjusting nut one slot. Re-check backlash with the dial indicator as above.
The third and final step of setting up your guitar is to cut the slots in the string nut to a depth where you get the optimal first fret clearance for each string. Rather obviously, you want that clearance to be as low as possible, because the higher it is, the more your fingers will hurt when fretting the strings at the first few frets. Moreover, the intonation of your guitar will suffer (that is, your chords will be off even with perfect tuning) when the strings are too high above the first fret. So if we want the strings to be as low as possible on the nut, then what is the lower bound? One constraint is of course that the open, unfretted strings should never buzz on the first fret. However, there is another thing to be kept in mind: raising the strings at the nut will also prevent the behind-the-fret buzz that I mentioned earlier. Therefore, your ideal first fret clearance is usually a tad more than what you would absolutely need to prevent the open string from buzzing. That is true especially if you prefer less neck relief. My preferred values for the first fret action are .022' for the sixth string (that's the deep E, the wound string) and .018 for the first string (that's the high E, the thin unwound string), with the rest of them pretty much evenly spaced in between.
How To Check Nut Slot Depth Charts
How To Check Nut Slot Depth Machine
When you buy a new guitar, you can almost be guaranteed that the nut slots are not deep enough. I have seen expensive guitars that came with as much as .035' of first fret clearance, truly a finger killer. To cut the nut slots deeper, get yourself a good set of nut slot files, e.g. from Stewart-MacDonald. For each nut slot, select a file that is as wide or a tad wider than the diameter of the respective string. (Making the slot too narrow will cause the string to bind in the slot, with very unpleasant consequences.) To work on a particular slot, take off the respective string, but make sure that all the other strings are on and tuned up, so that the neck is pretty much in the same position as it is normally when you play. Then cut the nut slot deeper with your file, angling it downward a bit towards the headstock.