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When I built my first kit, I sanded a 20" (that's inch) radius onto the fretboard after it was on the neck, as instructed. Now working on the my first scratch build and was wondering if this is a subjective radius? I've seen lots of builders up here putting anywhere from 16" to 20" on the fretboard - what determines what you will use and how do you arrive at that decision?

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Mitch

On my recent, almost finished, classical, I put a compound radius on the fingerboard. Its probably far, far from any conventional amount of radius. I made up a series of small blocks with various radii, checked them off my left hand index finger, and decided to use 6" at the nut. I don't have a value for the other end.

It sounds extreme, but in practice isn't. Feels very good to me.

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The conventional radius for most acoustics is 16" I think this came from Martin. I have built with a 12" for a client with severe arthritis in his index finger to make it possible for him to barr chord again. so to some degree it is subjective. the whole intent is to make fretting easier and ergonomics

Hey Mitch, I like the 16" radius. I think most will tell you to find what you like and stay with that. Different factories use different radii. Some OLFers use a compound radius and have built jigs to help shape the FB acording to the start and end point they like. Search the archives for compound radius jig if you are interested in that. I just keep mine simple at the 16". Works for me.

Donovan

I like to do a compound of 16 a the nut to 20 at the end of the fretboard. This supposedly helps to mitigate some buzzing problems when bending strings, but I have absolutely no proof of that...

-Mark

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Mitch bro I have heard what Mark mentioned too and can see the benefits of the 16/20 compound radius.

I have just always used 16" as my radius choosing to focus on other areas of building first before I tackle compound radius fret boards. As Michael indicated in our Martin dominated acoustic guitar world most are used to a 16" radius as well.

As a side note in the book Clapton's guitar Wayne Henderson supposedly occasionally builds with a dead flat, no radius fret board.

I use a compound radius on my steel string guitars. 14" at the nut, 20" at he other end.

Mark

If you have any radius at all in your fretboard and the string spacing at the bridge is larger than the spacing at the nut, then you will not be able to achieve optimum action without a compound radius. This is because the surface of a fretboard using a single radius describes a section of a cylinder, whereas the strings describe a conical section as they spread out. So in effect you you have a conical section over a cylinder... not an ideal setup. To figure out the ideal compound radius given a scale length and string spacing at the nut and saddle, I use formulas given in an article by Elaine Hartstein in one of the AL big red books.... I just looked it up, it is volume 3 P. 314. For my 24.9" scale guitars, it works out to about 20" on one end of the fretboard if I use 14" at the nut.

Of course lots of guitars are made with a single radius and have acceptable action. The larger the radius, the closer to ideal the relationship between strings and fretboard. If I were doing a 20" radius at the nut, I might not bother to go compound, but if I were doing a 10" inch radius at the nut and there's a big difference in spacing from nut to saddle I would expect pretty awful action on the outer strings without the proper compound radius.

Lex,
Thanks, That is a great explanation for using a compound fretboard. I wanted to ask that question in the other thread about building a jig to compound the radius of a fretboard. Mario and Bob brought up a great point, when Mario stated that yes he does sweat the small stuff whether it is .007" or .009". I guess I'll have to put one more jig on my list, just one more jig!!!!!
Peter

Yes, the issue of achieving a straight line under each string with a standard or compound radius board was discussed a bit in the compound radius router jig discussion going on now. The same thing happens with either a constant radius or a compound change that is above or below a certain point. The ideal would be for the change in fingerboard radius to be directly proportional to the change in string spacing. Of course I use the word "ideal" here only in terms of nice simple geometric shapes, not that those should dictate how we shape our boards.

This rule would limit how you radiused your board if you stuck to it. A 14" at the nut would have to be around 16_1/2" at the end. If you want a 14" to 20", or a constant 12 for example, the difference is slight enough to be able to simply level under each string after it's fretted, and it doesn't take much. A good leveling technique will automatically get rid of the true cylindrical or conical shape in favor of a level plane under each string.

I personally like the 14"-20" range of compound.

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