12" single radius vs. 12"-16" compound radius fretboard

[John Clifford]

I’ve been doing all my fretboards with a single 12” radius (cylindrical), and never could detect any problem with playability. Still, I’ve been bugged by all the people claiming that only “compound” or “conical” fretboards are suitable for discerning players. Since I can’t feel a difference, I made a scaled diagram in order to see it.

So this diagram represents a 25” scale fretboard that is 1-11/16” wide at the nut (green) and 2-1/4” wide at the 22nd fret (red), with the high E string set back 1/8” from the edge at all points. For a “conical” fretboard, if you start with a 12” radius at the nut, you will have a 16” radius at the 22nd fret. Those curves are shown with a point of tangency at the center. The grid lines represent 0.10”.

As you can see, the difference between the two curves at the point where the E string crosses the 22nd fret is about 0.01”. And if you bent the string to where it is perpendicular to the nut, that difference would reduce to about 0.005”. For the inner strings, the differences become almost unmeasurable. I really don’t see how a conical surface would make a difference for string bending, since that is usually done toward the center of the fretboard, where the curves converge. Also, most serious benders actually like relatively high action, so they can slip the bending finger under the adjacent string.

So what does this prove? Nothing, but I’m going to stick with the single 12” radius, just for the convenience. That allows me to use one radiused beam for shaping the fretboard, leveling the frets, clamping the fretboard onto the neck for glueing, and shaping the top of the nut and saddle. Also I can use one radiused fret press insert to perfectly press in all of the frets. I can see where a “compound” radius might make sense if you started with something like a 9.5” radius at the nut, but that’s not for me.

[Barry Daniels]

Is this in reference to acoustic guitars or electric.

[John Clifford]

Is this in reference to acoustic guitars or electric.

I put it under archtops, because that's mostly what I build - both acoustic and electric. Here are a couple of examples, one a parlor-size acoustic, the other a double cutaway electric. Both have 12" radius fretboards.

[Rodger Knox]

As your diagram shows, there's not much difference. The difference is really the amount you have to remove from the frets. No matter how you radius the fretboard, it's ultimately the string paths along the tops of the frets that have to be level, and the closer the fretboard is to level along the string paths, the less will need to be removed from the frets if they are installed uniformly. I spend a lot of time getting the board exactly right, and I usually don't need to do a full fret leveling. My last guitar had two frets that needed work to get the action down to .07" and .08", which is as low as I like on an acoustic.

[Barry Daniels]

As Rodger said, if you level the string paths then you in effect do have a compound radius fretboard. Players who insist on a radical compound radius are just parroting what they have read or heard from other shredders as a must have. Tell them your guitars have compound radius from 11.5" to 12.5". You won't be too far off.

[Gordon Bellerose]

Yeah, I agree with Barry.
My opinion is that compound radius fret boards are a marketing success, but not really a big deal if you have a properly done single 12 inch radius.
The smaller radii, like 7.5 or 9 inch, may benefit.