Thank you for the kind words. I get good results on nut setups because I spend what some might consider an inordinate amount of time on them. I know nobody would want me on their production line :laughing7:
Of course, slot width is important. Too narrow, even by .001", or exactly the size of the intended string, and you'll get string hangups. In other words, you don't want a .009" slot (or smaller) for a .009" string. The nut will tend to "grab" the string and you'll have intermittent tuning issues. You can lubricate the slot, but like contact cleaner on scratchy pots/switches, you're just putting lipstick on a pig. The problem hasn't been solved.
The depth of the slots is another thing, and something that's tough to get right without going too far. Nobody wants to start over (which is often your only choice if you do go too far), so the natural tendency is to leave them a bit shallow. The vast majority (I'm guessing 95% or better) of guitars out there are this way, so there's little kickback from the user base. It's what they expect. This causes a different kind of tuning issue because the farther you have to push a string down, the more you increase its tension, so you end up sharping notes. You usually can't hear it on individual notes, but it's enough to cause dissonance in chords that's fairly easy to hear and will aggravate the hell of sensitive ears. Then you end up chasing your tail trying to adjust intonation at the bridge and never getting happy because that's not the problem.
Then there's the slot shape, which is critically important regardless of depth. Any time you get a "singing" or "sitar" sound on open strings, it's a slot shape problem. The exit end of the slot facing the speaking length of the string has to be square to the string, or the string will bang against the slot as it vibrates. It's usually a very tiny anomaly physically, but for as small as it is it has a surprisingly loud effect. It also has a tendency to reflect harmonics differently at different frequencies, which is why it often sounds like a "sitar".
You can get a similar effect on wider nuts like you see on Gibsons if the slot is cut too square, or more accurately, square all the back to the exit end of the nut on the headstock side. Here, headstock angle can hurt you as the bend in the string causes a "hump" as it moves through the nut, making the pressure at the exit end to the speaking length too light and allowing it to vibrate in the slot. Same symptoms as described above.
Of course, you also want the bottom of the slot to be round so you have good contact with the string, and you need enough sidewall on the slots to keep strings in place, but not so tall that they become garbage collectors.
Get all that right, and string trees aren't necessary.
