Are these indentations on the frets of my Acoustic for intonation? Can I apply this to the frets of my Electric?

Question

The questions are in the title, picture is below, but here are the (TL/DR) details.

About 9 months ago, I bought an electric guitar "kit" and assembled it (fun, highly recommended). This included fret leveling, crowning, and polishing. A guitarist friend of mine acted like I might as well go over Einstein's Theory of Relativity and see if I could find some mistakes—it's that difficult! But it went well, in my opinion.

I got the intonation pretty close at the 12th fret through normal saddle adjustment, but ran out of travel on the 2nd and 3rd strings, and had to reverse the individual saddles to get them spot-on. The only problem I still have is the intonation on the first few frets, not so much on strings 4-6, but it's pretty bad on G(3rd), somewhat bad on B(2nd) and merely noticeable on E(1st). They sound sharp, bad on the 1st fret, better as you go up until about the 5th fret is again spot-on. Google tells me that this is pretty common (though I have no explanation as to why G is an especially fickle string!).

I've come to appreciate that if you squeeze the crap out of (example) the G string on second fret that this causes A to become really sharp, and if you just barely touch the fret, it's not so bad, but even when I'm barely touching the fret, which is not gonna happen in normal play, it's still almost 25 cents sharp.

Some of the advice on the internet tells me to flatten the entire string slightly so that the G is slightly flat and the A is only slightly sharp, but, like, I mean, what the hell???? Other advice I've seen is that I'm probably being too critical; nobody else will hear the difference. Trouble is, I don't believe it. Barre chords sound fine, and when I'm playing at or above 5th fret, even perfect. In this case, every string is fretted, and any slight sharpness due to squeezing the string against the fret is equal across the board, probably unnoticeable. But, when playing open chords (especially, for instance, "D", as 1st - 3rd strings all are fretted at 2nd or 3rd fret, yet 4th string is open), it sounds bad. Even open chord "E" has a big problem of the G string fretted at 1st fret (worst string, worst fret, followed by two open strings).

I've been considering trying to shape the individual frets under 3rd string frets 1-3 slightly back (toward the nut), but this seems really scary (worse than the Einstein thing!), especially seeing as how I'm pretty close now.

THEN!
_{(cue dramatic orchestra hit)}

I was changing the strings on my Ibanez Acoustic I've had for about a year and a half. While cleaning the fretboard, the light caught the frets in such a way that I could see slight dents(?) under the 1st, 2nd and 3rd strings. Heaviest (dark red circles) on the 1st fret and getting lighter on higher frets until they seemed to completely dissapear on the 6th fret (green circles):

_{(click to enlarge)}

The flash obscured the similar dents under the 3rd string, but they're there.

Now the wheels are turning again: Are those indentations there on purpose for intonation? Can I apply this same technique to my electric, relatively* easily? Any other thoughts/methods I could try to help this?

Or is it more likely that I am completely, irreversibly insane?

_{* thanks, Einstein!}

Answer 1

That's fret wear. The strings have slowly eroded away some of the fret material, leaving those dents. Over a long enough time, they become deep enough to cause problems.

When the fret wear is bad enough, you can have your frets "leveled", which means sanding down the tops of the frets so that the dents are sanded out. Then the frets a re-crowned and dressed and polished and they will be good for a while. Eventually frets wear enough that they have to be replaced, which is called a "refret".

All guitars have compromises on intonation - it's a consequence of the construction and mechanics of the guitar. One thing you can investigate is a compensating nut, which is a nut which has tiny extensions so that the nut side of the strings has intonation adjustments made kind of like the saddle side of an adjustable saddle bridge.

Another factor in the intonation of guitars is the ideal placement of the frets, adjustment of the saddles, and the overall action.

Personally, I do like your friend suggested and I deliberately tune the open strings of my guitars slightly off from where the tuner would have me tune them in order to make a tradeoff for better intonation around the 7th - 9th frets, where I like to play the most. I don't do this on my acoustic guitars, but I do it on my electrics.

Another thing I agree with is that mainly listeners don't notice the intonation quirks of guitars, but in some ways they do but it doesn't matter because that's a part of how guitars sound. It's one of the little details that synths and sample libraries don't quite get right when they try to imitate guitars.

Answer 2

Those fret indentations are wear caused by playing. No manufactures would put them in on purpose.

My first move would be to consider that the neck is actually too close to the bridge. Maybe it could be moved, making it longer, by a few millimetres. Measure the distance between nut and 12th fret. It should be, give or take a couple of mm, the same as 12th fret to saddle on the 3rd/4th string. If that is short, then 'elongating' the neck should improve things, and the saddles can be adjusted accordingly.

I can't see how changing the nut will improve matters - all that will do is make the 1st fret longer, not adjust the neck or other frets.

If the action is high, then pressing the strings down will effectively sharpen them too much.

Answer 3

Since the intonation is correct using bar chords but not with open chords I would check the height of the nut string slots. If a couple strings are riding higher they will go sharper than the others and this problem will be more pronounced as you get closer to the nut. For example, you’ll likely find playing an open E chord more out out tune than an open G. Bar chords rest evenly on frets which have very even heights but even lower played bar chords ( such as an F) would also be adversely affected by the varying string heights of an uneven nut slot issue. You’ll need specialized nut files to do this correctly. Stewart McDonald luthier supplies is a great source.

Cheers, Thelowedown