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

Please put your pickup/wiring discussions in the Electronics section; and put discussions about repair issues, including fixing errors in new instruments, in the Repairs section.
Post Reply
John Clifford
Posts: 180
Joined: Mon Dec 18, 2017 3:08 pm

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

Post by 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.
Attachments
Neck Radiu.jpg
User avatar
Barry Daniels
Posts: 3186
Joined: Thu Jan 05, 2012 10:58 am
Location: The Woodlands, Texas

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

Post by Barry Daniels »

Is this in reference to acoustic guitars or electric.
MIMF Staff
John Clifford
Posts: 180
Joined: Mon Dec 18, 2017 3:08 pm

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

Post by John Clifford »

Barry Daniels wrote: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.
Attachments
DSC_2310.jpg
DSC_2869.jpg
Rodger Knox
Posts: 497
Joined: Mon Jan 09, 2012 2:02 pm
Location: Baltimore, Maryland

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

Post by 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.
A man hears what he wants to hear, and disreguards the rest. Paul Simon
User avatar
Barry Daniels
Posts: 3186
Joined: Thu Jan 05, 2012 10:58 am
Location: The Woodlands, Texas

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

Post by 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.
MIMF Staff
Gordon Bellerose
Posts: 1186
Joined: Wed May 30, 2012 11:47 pm
Location: Edmonton AB. Canada

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

Post by 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.
I need your help. I can't possibly make all the mistakes myself!
Post Reply

Return to “Archtop Guitars and Bass Guitars”