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I've been reading about fingerboard radii, and have a question for you guys. If the nut, fretboard, and saddle are all at the same radius, will the fretboard play well, or does the fingerboard have to be compound?

If most concur that making a fingerboard radius compound is the best way, any ideas about a jig I could build without having to purchase a plan? I'm poor.

Thanks,

Sean

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I've been doing straight radius for years and so have countless others. Yes it works just fine. I have however been delving into compound radius boards so I am gonna sit back and watch this thread too. The way I do it is use several radius blocks to get close and then finish it off with a long heavy straight milled steal block with 80 grit sand paper about 2cm wide, I run that up and down the board on the same angle of the strings till it sands flush.

Thanks for the quick response. I've only built one guitar. I made my own radius block, and glued sandpaper to it. I started with 80 and worked down to 400 before fretting and finishing. It was a lot of work, and I was careful to keep it centered over the fretboard and tried to sand as evenly as I could. I used a radius gauge to check it along the way. It plays just fine, and although I never put a string action gauge on it, everyone else who has played it seems to think it plays fine also. I'm wondering if I was just lucky.

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I use a straight 12" or 16" radius. I made my blocks out of 2 x 3/4" ply and 1' long. Funnily I switched from using a compound radius maybe 35 guitars ago. Before that, I used the clever jig at Pantheon (Bourgeois)…
In theory you can get a lower action with a compound radius, in practice I haven't found a difference. And I routinely get .055" to .080" at the 12th fret, sometimes lower when requested. The deciding factor IMHO is how well seated your frets are (and their manufacturing quality), and how perfect is you final fret levelling job.
You can make your compound jig for a belt sander or router. It involves deciding what radius you want at the nut and which one you want at the saddle.

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Laurent Brondel
West Paris, Maine - USA
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It seems Stew Mac had a article on why to compound radius...has to do with conical shape as the fretboard widens towards the bridge..
I just about finished on a Om where , using sanding blocks , I went from 12 to 16 to 20 ...but sanding was a pain and have since made a radius jig , ala , Todd Stock ...
curious to see some people chime in ......

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MK5acoustics.com

You don't really need jigs or radius blocks to do a compound radius fretboard. I use a 16" long sanding block that is 1 1/2" wide. It has 36 grit sanding belt attached to it and will remove wood in a hurry!! I shape the fingerboard with that after the neck is attached to the guitar. If you keep the block in line with the run of the strings, and check your progress with a radius gauge at three or four different spots on the fretboard as you go, you can shape a conical board in a few minutes. Once it's the right shape, just follow up with finer grits to smooth it out.

I typically make mine 14" at the nut and 20" at the other end. Sometimes I change that depending on the guitar style and the players preferences. Using a simple sanding block, it's easy to make it any shape I want.

M

This is probably a stupid question, but I'm assuming if you do make a compound radius, then at the higher frets you have to match that radius with the saddle's radius?

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Or maybe the radius of the saddle should be the radius at the 12th fret?

If you do a compund radius the saddle is flatter than the end of the fretboard.

I make my guitar fretboards with a cylindrical radius and dress a compound radius into the tops of the frets. I use the 18 inch long aluminum beams from stew mac, after roughing in the arch with a block plane.

I make my bass guitar fretboards with a compund radius, and I use a belt sander for that, checking with my radius templates and 36 inch straightedge for accuracy.
.

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Shouldn't it be more like 14" at nut, 20" at 12th, and 24" at saddle? Continue the theoretical radius widening across the empty space.

I've been pondering on fretboard geometry lately, and plan to switch to compound. Also to attempt some tricks, increasing the relief on the bass side to allow for the greater vibrating arc without having to raise the saddle height compared to the treble strings, and leveling out the relief around the 5th to 7th frets, since that's pretty much the point of maximum excursion for the vibrating strings when plucked in the normal playing area, and makes for lower action at the high frets. It must all be done with reference to how the neck will be under string tension though, by manual flexing or by supporting at the headstock and tail and placing weights on the shoulders to bow the neck. I think I'll practice on my prototype guitar, since it's quite possible that I will fail much worse than simply making a flat cylindrical radius.

You can also do a cylindrical radius in the fingerboard, but sand a compound radius into the frets themselves, leveling out the "hump" that the outer strings encounter due to cutting across the cylinder at an angle. EDIT: Ninja'd by theguitarwhisperer on this point

Laurent already answered the question, the relevant locations are nut and saddle, the fb is determined by these. Just went over this in the Charles Fox class yesterday.
Rob

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What cylindrical radius do you use? I am surprised that there is that much meat on the frets to compound during leveling. Not saying you are wrong mind you, just that I am surprised. I like to use a zero fret and it occurs to me that you could calculate the "nut" radius and saddle radius and go from there. Make a saddle of proper radius but lower than the final one (low enough to be in line with the frets once leveled). You could then run a long beam between the zero fret and saddle following the string paths (no abrasive on the zero fret and saddle). Then polish the frets, instal real saddle and dial in your relief. . .

I'm sure I am missing something, I'd like to hear everyone's critique.

Edit: It also occurs to me that I could just make a long jig with both radii and sand the fretboard down to a compound radius.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

That's the whole idea. I assume most people who get good action with a cylindrical board are doing the same thing but instead of removing material from the board, they remove a few thousandths from the top of the frets.

And if the goal is a straight line under each string path, the radii can be whatever you want. It doesn't have to be conical or even symmetrical.

I like the feel of the flatter saddle and rounder nut but that's just personal preference.

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In theory, the radius of the saddle would be greater than the radius at the end of the fingerboard. My experience is that, in practice, it doesn't work like that. I make my fingerboard 14" at the nut and 20" at the 20th fret. Theoretically, the saddle should be something like 24". I radius my saddles to 16" and it works great. If I make the saddle flatter than that the D and G strings will buzz, usually around frets 3 - 5.

This has to do with the fact that string height on the treble strings is lower than on bass strings. Imagine that you made the saddle with a 24" radius and set all the strings at the height required for the bass strings. The treble strings are too high, so you lower the high E a little, the B a little less the G even less. The D and A need about the same height as the low E so you leave them alone. Now measure the radius on the saddle and it will approximate 16" with a little "bump" near the G and D strings. This works well. Tapering the 24' radius saddle so that the high and low E strings are the right height does not.

M

Thanks Mark,

I appreciate your advice. I LOVE your guitars. You're a true artist.

Sean

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change isn't synonymous with improvement
instagram.com/bucketguitars/

I usually use a cylindrical 16" radius, unless a compound radius is requested by the customer. As a player, I can't tell the difference.
The only "issue" I have with a cylindrical radius is the edge of the FB tapers toward the saddle. I compensate for this when shaping the fingerboard.
To mark the radius accurately (no mater what the radius or radii) I have a straight oak stick with a pencil mounted in a hole drilled in the end of it at the correct height over the plane of the FB. Slide the stick across the frets, following the string paths, with the pencil in contact with the saddle. And VOILA! a good starting point for shaping the saddle.