I posted earlier about needing to glue the bridge back onto my classical guitar. I have a different issue, though it might be kind of related.

The guitar had intonation problems since I bought it a couple years back. If the low E is perfectly in tune while open, it'll be noticeably sharp by the fifth fret, and get worse down the line. Other strings had similar issues. I think maybe from the fifth to 12 frets, they are off by 10-20 cents. Since it's been broken for a couple months, I don't recall exactly.

Anyway, I was reading on bridge repair and it said how placement of the bridge can affect intonation. Which makes me wonder, if instead of gluing the bridge back where it was, maybe I could glue it a little closer or further from the neck, and that might fix the intonation issue? I don't know, it sounds like a crazy idea now that I type it.

The follow up question is, how the heck do you fix intonation on a classical guitar? There's no truss rod. Since the guitar appeared in mint condition when I got it, I can only assume the bad intonation resulted from the frets originally being laid in the wrong positions. Is there an alternative explanation (note, it's a 40 year old guitar)?

If the frets were laid in the wrong position, then it would seem the only fix is to take up all the frets, fill them in or otherwise smooth out the neck, then calculate the correct location for correct placement of the frets, and then place them there... Is that right? Seems a lot of work on a $200 guitar.

Oh, it occurs to me to wonder if there are other ways to change the intonation, to fix it, like what if all the frets were just a bit higher? Would that do it? Or lower? Maybe the intonation is off because the frets have sunk, or been pushed higher by wood expansion, over the years, and the placement is fine so long as I fix the height?

On a related note, could the height of the nut affect intonation since it could theoretically change the proportionate distance from nut to bridge? Could there be some other adjustment to make on the bridge that might help with intonation other than gluing it down in a different place than where it was?

Bernie Sanders for President!
measure from your nut to your 12th fret, then make the distance from your 12th fret to your saddle that same distance, that is HUGE part of intonation.
Quote by R45VT
The height of both the nut and the bridge can affect intonation on stringed instruments as when you fret a note the string has to stretch to reach the fret. As Viban pointed out, start with the break point of the bridge at the theoretical scale length and adjust from there. Its probably helpful to use some double sided tape to hold it in place while you experiment with the best position for it.

The one piece saddles on classical and acoustic guitars are always a compromise across the strings, you will have to decide on the best placement by averaging out the errors. For example, you may be able to get the first and sixth string perfect but the rest could be sharp. In that case I would allow the E's to intonate slightly flat in order to get more of the strings closer to perfect.