New nut not 90° at fretboard

[dannyg1]

Originally Posted by mirwa

Post a photo, we will tell you.

A nut overhanging the side edges of the fretboard, is just a representation of average workmanship / attention to detail, it does not however, affect the intonation.

Intonation is affected by the relationship of the nut to the ned of the fretboard and the substructure it sits on.

Steve

Ok. Posted the photo, ready for your comment.

[mirwa]

Originally Posted by dannyg1

Ok. Posted the photo, ready for your comment.

I did

Originally Posted by mirwa

It is hard to assess the fit of the nut to slot, with the shadow that's falling over that area in your photo.

Steve

[charles Tauber]

Originally Posted by dannyg1

I'm also considering buying some luthiers tools from stew Mac, 1st the intonator and then the saddlematic, to confirm. Seems like a lot of money to spend on something a good luthier might be able to sight spot though.
Quick plea for an actual luthier to comment please?

Don't waste your money on those: they aren't the right tools for your situation.

First, it isn't clear from your description if you took your guitar to a luthier or repair person and had them make you a new nut and saddle. If so, I suggest you return to him or her and have him or her rework what was done to improve the intonation.

If you prefer to do it yourself, here's an overview of what needs to be done ...

Start by looking closely at where each string breaks over the nut. Each string must break at the fingerboard-face of the nut. If it does not, it can have repercussions on the intonation. If it does not, file each slot so that it does.

Next, do as was previously suggested by others to ensure that the strings in the nut slots do not sit too high relative to the height of the first fret. Based on your description, they likely do. If they are too high, the notes in the first few frets, in particular, will sound sharp. If they are too high, file them to the correct height - the same height as the first fret, or a few thousandths of an inch higher.

Next, accurately determine the scale length of the instrument. Measure to the nearest mm or 1/64". Measure from the end of the fingerboard/face of the nut to the 12th fret. Double that measurement is your scale length. From the end of the fingerboard/face of the nut, measure the distance to where each string breaks over the saddle. This should be MORE than the scale length. The amount by which it exceeds the scale length is the amount of compensation each string has. The amount of necessary compensation depends upon several factors including string gauge, string type, string height, scale length and pitch to which the strings are tuned. Consequently, each string requires its own vibrating string length.

Next, using your tuner, determine by how many cents - 100ths of a semitone - each string is out when the 12th fret fretted note is compared to the open string or 12th fret harmonic. Write it down. You state that the fretted notes are flat at the 12th fret. That means that their vibrating lengths are too short: increased compensation is required until they play in tune. A "typical" ball-park amount of compensation is about 3 mm on the high E and about 5 mm on the low E: typically, the B string will require more than its neighbouring high E and G.

If the saddle position and saddle thickness allow, file the breaking point of each string so that it plays in tune at the 12th fret. This should give you "acceptable" intonation. How "acceptable" depends upon your ear, how accurate your adjustments are and other factors beyond this discussion.

A more detailed description can be found here, under Basic Guitar Setup 101: http://charlestauber.com/luthier/Resources.html

[MC5C]

This actual luthier says can't tell from a photo but sharp near the nut and flat by the 12th fret says it needs a setup and suggests the string height at the nut is too high. FWIW, both times I had new nuts put on by professional guitar technicians (before I started building guitars) I had to adjust the slot heights. They were set up too high, and in one case indeed caused the instrument to play sharp on the first fret.

There is also the whole concept of compensated nuts (which applies more to electric guitars with short scales and light strings than a typical acoustic, depending on the expert you choose to believe) and how you are tuning. The whole inharmonicity of equal temperament can come into play if you are tuning to open chords.

[John Arnold]

If the nut is leaning over the fretboard end (shortening the distance from the nut to the first fret), that would cause flat intonation near the nut, not sharp. As Charles indicated, either the nut is too high, or the slots are not angled enough to cause the break point to be at the end of the fingerboard.

[Bruce Sexauer]

While it is possible that the end of the fingerboard is cut a degree off 90, looking at the picture, it is extremely unlikely. Even if it is, few to no people have hearing good enough to pick up the difference in intonation that would cause. As others have said, any discrepancy in the nut slot height would make more difference that a mildly angled fingerboard end/nut, and is the most likely issue.

By the way, this answer does not actually need a luthier in order to be accurate, any decent guitar tech understands this stuff just fine.