I am still perplexed as to why the floor of the nut slot needs to be .5mm higher than the plane of the tops of the first two frets, which is what I assumed you meant ( ignore the fretting at the third and measuring the gap at the first fret ... that wasn't what I was talking about )
When you do a fret dress and crown on a classical guitar (which I have never done, although hundreds on steel string guitars) I assume that you set the neck straight first of all, by whatever method you choose (I use a specialized jig when doing steel string guitars) then dress the frets level (ie the tops are all in the same plane) and then crown them, and you then rely on string tension to pull the neck into correct relief (since classical guitars do not normally have adjustable truss rods).
But the nut slot floors are not in this plane, they are .5mm higher, and this is to prevent buzzing. So the question arises, why don't the strings buzz when they are fretted at the first fret ... take it one step further , if you used a capo to hold the strings down at the first fret, would the strings then buzz? And if not, why not?
The nut, after all, is in essence only another fret which has the additional function of maintaining string spacing.
So if you built a classical guitar with a zero fret, are you saying that the zero fret would have to be .5mm above the level of all the other frets? By that logic, the second fret should be .5mm below the level of the first fret, and the third fret .5mm below the level of the second fret, und so weiter.
I am quite sure that there is something I am missing and I eagerly await elucidation. Specifically about the zero fret question.
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