Official Luthiers Forum!

I know it's a broad topic with no right answer. However, sometimes it's nice to know that there is no exact answer so you can feel more confident with the answer you come up with.

Anyway, it's been helpful to read some thoughts on the topic and to hear what some people see as too high or too low.

I think I'll need to start trying a compound radius like lex_luther suggested to get it extra low for those who want that way.

Out of curiosity, what do you think a compound radius will do to allow you to get lower action? There is a potential advantage, depending on how small a radius you use normally and how you play. I am just curious what you think the compound radius will do for you (never good if you go away from a topic like this with the wrong idea about something).

A tip of the hat to you Kent-That was funny
Terry

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It's not what you don't know that hurts you, it's what you do know that's wrong.

If the string spacing stays constant from nut to saddle, then there is no advantage to a compound radius. Here the strings and the fretboard both define a cylindrical section. A cylinder (defined by the bottom of the strings) over a slightly smaller cylinder (defined by the fret crowns) is optimal; the bottom of each string is the same distance from each fret regardless of where it is on the fretboard. This does not take relief into account which is another discussion altogether.

But... since the string spacing increases as you get closer to the saddle, say from 1.75" at the nut to 2.25" at the saddle, well now the strings define a conical section with the radius decreasing away from the nut. The fretboard radius should decrease proportionally down the fretboard as well. You can't have a conical section (strings) over a cylindrical section (constant radius fretboard) and expect things to be optimal.

Compound doesn't have to be conical. Any compound that gets you closer to a straight line under the string path is a potential improvment over cylindrical.

But it gets pretty complex once you start figuring in relief and, ideally, less relief on the treble side than base.

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http://www.chassonguitars.com

Perfect action for me and my playing style is .060" or about 1/16" at the 12th fret across all six strings.

That has worked for many of my customers, but perfect action for many others has fallen closer to
.090" or about 3/32" at the 12th fret.

Most players appreciate some combination of heights between the two, though. Typical for the players
I've dealt with is about .070" at the 12th fret on the high "E" and about .085" at the 12th fret on the low "E"
string.

That's where all of my guitars that aren't on their way to a specific customer get set up to. Dealer orders
and spec guitars need to be set up to a generic set of dimensions so that they can feel good to a broad
variety of players. Low enough to give the very light fingerstyle guy who loves low action a good idea that
it can be tweaked to meet his needs, but high enough to be driven by a pretty aggressive flatpicker with
little to no buzzing.

If your nut slots are cut properly cut and the saddle height is established to present the desired action at
the 12th fret, the action should follow suit consistently at the 20 th fret regardless of neck angle. I don't
build in a drop off from the 14th to 20th frets so it is a consistent thing on my guitars.

Regards,
Kevin Gallagher/Omega Guitars

I guess I am just looking for every advantage I can use to design a guitar that can go down that extra 64th to get the action down to the 1/16th range easily if someone wanted it this low.

As a mathematics teacher and a guitar builder, I'm still debating in my mind weather a compound radius is the best way to go. I am seeing some positives and negatives that I need to research more. It seems like the compound radius is good for the high strings because it keeps the string more parallel to the fretboard plane. However, the constant radius may be a positive thing for the bass strings because it causes the plane to "fall away" from the bass string toward the upper part of the fretboard (where the string vibrates more).

I need to conduct some more research. It seems like a lot of builders support this compound radius.

Thanks for sharing these thoughts, Kevin. I appreciate the perspective. There is a difference between the custom set-up and the guitar shop set-up.

Thanks,
Jeremy

Many necks do and should have "fallaway" to cope with string pressure over time .Consider where it starts and how much before measuring string height at frets above #12.To ignore this fact may give poor results.

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How long is that in luthyears?