My rant on why EVERY fingerboard should have a compound radius

[cmjohnson]

Amazing this thread lives again!

In order for the edges of the fretboard to be truly straight, then the radius of the board has to change at the same rate as it gets wider. It's geometry. Make the conic section and cut a fretboard out of it, and there are three ways to cut that fretboard: Ideal, with the width of the board changing at the same rate as the radius, narrow bottom, where the body end is narrower than ideal, and wide bottom, where the body end is narrower than ideal.

Look at it in the simplest way: You cut the board out of the conic block of wood you made. You cut the board so it is of even width all the way down its length. (Narrow bottom) It's still compound radiused. But what happens to the edges of the board?
They're too thick as you get toward the body end. The board gets thicker toward the body, but only as you get out to the edges of the board.

If the thickness of the board going down the centerline was absolutely uniform, you'd find that the edges of the board are thicker at the body end than at the nut end.

If the board is cut with a fat bottom, the reverse happens. The board thins out on the edge as you get closer to the body.
So, if the thickness of this board going down the centerline is absolutely uniform, you will then see that on this one, the edges of the board get thinner toward the body end.


How to sand and level a board like this? A swing-arm rig with arms of different lengths (radiuses from the center point of the swing) over a belt sander with a horizontal table would work quite well. But that rig would obviously not be too practical for levelling the fret job. Engineering the swing arm rig to properly and safely hold the entire guitar would be a nice little challenge.

 

[pshupe]

Amazing this thread lives again!

In order for the edges of the fretboard to be truly straight, then the radius of the board has to change at the same rate as it gets wider. It's geometry.

The radius can stay the same. The board just has to get thicker as it gets wider. For an 18" fret board the difference between 1 11/16" and 2 1/4", nut to end of the board, is about 0.024" considering a 12" radius. That equates to about 0.076 degrees change in neck angle. Shouldn't really affect much.

Regards Peter.

 

[crosstownblues]

Having owned several compound radius fretboard necks, I’m not a fan. I find nothing wrong with a straight radius. Am I alone here?

 

[efstop]

OK, after the last two technical posts, I'm certain I never want a compound radius finger board

 

[edro]

I remember last year a bud brought in a small radius high dollar and said he had it set up at a different shop. He said it played great part way up the neck but way up his bends would fret out.... I checked the neck out, played it and told him he was 'bending into the hill' and that his action was too low for that radius the way he played... He couldn't see in his head what I was describing. I bent a note way down toward nut and said look at vector off static line from target note bend point to saddle. I then bent way up the neck and said now look at vector line from saddle to target note bend point. Hence 'bending into the hill'...

I like the CR necks... I like the way they play. I don't consciously 'feel' a remarkable difference but I see the logic... I was never a fan of small radius boards anyway as far as my 'druthers'...

 

[Roxy13]

Having owned several compound radius fretboard necks, I’m not a fan. I find nothing wrong with a straight radius. Am I alone here?

No.

 

[fatdaddypreacher]

uhhhh, excuse me....i'm supposed to be putting a radius on my fretboards????....

 

[moreles]

I'm waiting for the movie version of the OP. In the meantime, I'll just make the ignorant observation that my guitars work. The 7.5 radius ones are extreme outliers and better for chording and rhythm, the rest -- 9 --> 12+ -- all play well. Given the ability to affect intonation significantly with just finger pressure, I lose no sleep over mini-microtonal impacts of small things like radius differences. I don't think they get heard.

 

[Freddy G]

I'm waiting for the movie version of the OP. In the meantime, I'll just make the ignorant observation that my guitars work. The 7.5 radius ones are extreme outliers and better for chording and rhythm, the rest -- 9 --> 12+ -- all play well. Given the ability to affect intonation significantly with just finger pressure, I lose no sleep over mini-microtonal impacts of small things like radius differences. I don't think they get heard.

That's just it. Once you get to 9.5" the issue disappears..... for me. It depends on how low you like your action. Certainly by 12" radius with any action. I have clients who like a feather touch action.....super duper low. They are mostly shredders. Acoustically the guitars sound quite "chokey" but with the amount of gain they typically use.....you don't hear it. So for those guys a CR makes sense IF they like the feel of a smaller radius at the nut end. But for the most part, they don't really care about a smaller radius at the nut end. None of them are playing Hendrix or Keef style where you wrap your thumb right around the neck. These guys are pretty much in the neo-classical left hand position where the thumb stays centered on the back of the neck with fingers all straight and stretched out.

 

[cmjohnson]

I did specify in my recent reinterpretation that if the centerline thickness of the fretboard is kept constant, then the edges will vary in thickness. But that's actually true even with a tapered fingerboard with a constant radius.

Suddenly I find myself wondering how many luthiers, and even guitar factories, don't pay attention to that little detail and attempt to control it?

I've certainly noticed guitars where the fingerboard is thinner at the body than at the nut. Lots of times.