What happens when a fret wears down?

Question

So I'm playing on a very old Harmony baritone ukulele. It has not been treated terribly well, and it is probably from the 50's. I'm having two problems.

First, the lowest string (I play plectrum tuning, so its a wire-wound string tuned to C3) will be in tune when open. Gradually it gets more and more sharp as I go up the fretboard. By the time I get to the 12th fret, it's so out-of-tune that it's unplayable. +30 cents at least. I suspect this may be some degree of warping of the neck.

The more pressing problem is that the second fret alone is very sharp. The first, third, fourth, and fifth are pretty close but fret 2 is way sharp. Is this due to the fret being worn down? I do use it a lot as I play, considerably more than the others in that neighborhood.

The higher strings don't have this issue. In the second picture, the arrow is pointing to the second fret. The issue is on the gold string, which appears lowest in the picture.

Answer 1

When a fret wears down, it does affect the tuning, as the string's new witness point may no longer be in the center of the fret wire. The fret's width is roughly 8% of the distance between frets in that picture, so we'd expect this effect to push it out of tune by up to 8 cents. Typically flat.

On top of that, the string now has to be depressed further to contact the fret. It's hard to give a number on how sharp this will push the string, as it depends on the fret location, string composition, string tension, and action at that fret. On guitars, this generally doesn't overcome the flatness from the first factor, but a ukulele has lower tension strings which will go sharp more easily.

If you want to get this uke back into playing shape, you should probably get the frets dressed. But if that's too much of an investment, there are some easier steps to tuning better, which you should do anyway. You already know it's intonated sharp, so adjust the bridge. Check your action and neck relief. Check if the nut slots are too shallow (or have someone experienced to this for you), this can make the first few frets play sharp. They probably are, since the frets wear faster than the nut.

Answer 2

What happens when a fret wears down? Pressing on that fret makes the string sound from the fret above - the next highest point on the fretboard. Making the note played usually a semitone higher than the one anticipated.

But, as the tuning goes out progressively, it's more likely that the bridge is in the wrong place. It should be exactly the same length from fret 12 as the measurement nut to fret 12. Best way to check is to play the 12th fret harmonic, and compare it with the fretted note. If the fretted note is sharp, then the bridge needs moving away, so that it's further away from the end of the fretboard. It's called adjusting the intonation, and there are many videos online showing this better than I can explain.