Fret Crown Profile

[Stephen Silva]

I am fingerstyle acoustic player of 40 years and have toyed around with saddles and nuts over the years, both with regard to designs and shapes, as well as materials. Recently I have decided to level and crown the frets on a few of my acoustics. Being a mechanical engineer, I have become highly interested in the optimum profile of the fret tops. There seems to be little information on the best profile and how to achieve it. I am wondering if anybody out there pays any attention to this, or if it matters much. I have made a small sanding fixture out of scrap cherry, that allows me to create the pitch toward the string contact point. I have tried 20 and 30 degrees from horizontal, using 220 and 320 grit paper double stick taped to the fixture. I was considering trying an even steeper angle of 45 degrees. I leave a tiny hairline in the top-center of the fret before rounding up and down the fingerboard with 320 around my finger, up through 3M micron polishing grades.

[Gordon Bellerose]

I will first tell you that I have never measured angles when I am crowning frets. I do not get that technical.
What I aim for is a rounded fret top. with the crown dead center of the fret.
This gives me the accuracy required so notes are not flat, or sharp.
The next thing is comfort.
Being a player of 40 years, you know that comfort on the fret board is extremely important.
There can be no sharp fret ends, and your hand should glide up and down the fret board.
For me, this means nicely rounded, smooth edges everywhere. I do not want a knife edge.

One thing I will say is that if you take too much material off the fret near the top, when the fret starts to wear as they all do, the groove will get deeper sooner.
The larger the amount of material just under the crown, the fret will have more resistance to wear.

Did I say that clearly? In other words, the "shoulder" of the fret should not be too narrow.

That's my opinion, for what it's worth.

[Stephen Silva]

Thanks for your comment Gordon. Yes, I do realize that I am sacrificing "life" for the possible advantage of a clearer tone. It will take a while to see how long it takes the frets to start showing signs of wear.

[Barry Daniels]

If the fret is crowned and not flat, then the point of contact between the string and fret is only a few thousandths of an inch wide. The rest of the fret does not make contact and really has no effect. So really whether it is crowned a little or a lot makes no difference in my opinion. I agree with Gordon that there are more important details to playing comfort. This is based on my 40 years of doing fret jobs.

[Alan Carruth]

There are schools of thought on this, as on everything else, and everybody 'knows' that their way is the correct one.

The most usual means of crowning the frets are with a safe-edge three square (triangular) file, or with a fret rounding file of one sort or another. Many of the pros I know swear by the safe edge file. It's easy to make one; you just use a sharpening stone to smooth off and round over the corners of the file so that they no longer cut. The more polished you get them the less trouble you'll have with marking up the wood. Using one of these takes a bit of practice, but it's simple to understand. The idea is to roll the file sideways as you push it across the fret top. I usually find it easier to file near the center of the fret first and work out toward the edge, so the file gets rolled from a point where the working face is almost level with the fretboard surface to almost perpendicular. The beauty of this is that you can easily make whatever radius (or non-radius) you want. It's also possible to have the high point of the crown off center along the fret, for those times when the board was not cut accurately, but the difference (or the value of the guitar) is not enough to justify removing the fret and re-cutting the slot.

Most builders I know use a fret rounding file of one sort or another. This is a shaped tool, either a cut file or a diamond tool, with a radius that is pretty close to that of the fret material. These are easy to use, fairly quick, and do a pretty good job. The radius you get is pretty well fixed, of course, and may not match the width of the fret you're working on. That's one of the main objections the pros have: it doesn't look right, particularly when the top of the fret, although rounded, is a quite a bit flatter than a true radius would be. They also, of course, do tend to center pretty well on the fret, which is normally an advantage, but sometimes not.

So far as I can tell, what counts in the end is that the fret top is rounded, no matter the radius (within reason), and the peak is where it's supposed to be.

[Trevor Gore]

Interesting question.

Many years ago, in my early experiments with intonation/compensation, I filed the frets on a guitar to a triangular profile (with a triangular file ) with a pretty sharp top. IIRC, I didn't hear much (if any) difference to a normally profiled "new" fret.

Recently, I've had a few guitars in where the frets had been "butchered" by some so-called guitar tech. The technique that it appears was used on those guitars was to level the frets with a stone or file in the usual way, then "crown" them just by sanding up and down the board maybe with a soft-ish backer, maybe with just fingers, until the edge was knocked off the flats. These frets were total tone suckers, especially on classical guitars, where it's hard to hear the fretbuzz, but everything fretted is seriously damped and just sounds dead. On the steel string guitars, some frets buzzed (as there was no single termination point) whilst the rest just didn't ring properly.

Now, I have an old diamond coated fret crowning file from StewMac, which has done plenty of miles. One side is for "wide" fret wire, the other is for "standard" fret wire. Whilst not properly measured, as I was re-crowning the frets on these guitars (all standard wire BTW) I was getting the distinct impression that I wouldn't want to go any "blunter" than the "wide" crown radius, if I was to avoid the dull sound of flat fret tops. So I just popped into the workshop to measure the radii on my fret crowning file (by dropping drill bits in the groove until I got the best fits). The "wide" side fits a 6mm drill (i.e. 3mm radius) and the "standard" side fits a 4mm drill (i.e. 2mm radius). So the "cut-off point" (for me at least) seems to be a 3mm radius to fret tops.

[Mike Conner]

Stephen,
As a fellow engineer, I appreciate your efforts towards precision. However, over 4 decades I have found that an intense level of effort in fret crowning and related details, etc just doesn't pay off in terms the practical nature of the end result - we are going to push strings down onto frets with imprecise fingers while smacking the other end with a flat pick or plucking with fingers. The challenge is in making sure the result is "good enough" and meets the expectations of the player. Often for acoustic guitars a good results has been relatively easy to attain. Only in the case of electric guitars with the player wanting absolutely the lowest action possible have I had to worry over each fret etc. - of course, these were jazz fusion type players with high level technique, impecable intonation and the desire to use the entire fretboard.

Trevor,
I have seen the guitar tech butcherie you refer to and it is frustrating to see, but done carefully and completley the sandpaper method works really well for me. I have the usual collection of fret crowning files, but find in most cases that the resulting surface still needs to be sanded smooth, and then polished out in the usual way. I agree that if the frets are not completely crowned the tone will suffer, and in the worst cases a sitar like buzz can be heard, especially with lighter strings. Either method will yield good results as long as it results in nicely crowned frets - we use the methods we trust to get there.