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I've done a few necks now, and consistently come up with similar fret board issues that I'm a little unhappy with. I thickness my fretboard blank, lay out my fret slots, cut them, trim the board to the profile of my neck, glue it on, and then radius it with a sanding block. When I get to this stage I find that by the time the end of the fretboard is the radius I want, this portion of fretboard is thinner than it is down by the nut. On the neck in front of me it's .0105" thinner at the end compared to the thickness at the first fret. The guitar will ultimately play okay, but it looks goofy to my eye. I'm wondering if its because the fret board once trimmed to the taper of the neck is thicker at the end then it is at the first fret and so it requires more sanding to get to the radius I'm aiming for. If I radiused the board before trimming it would this problem be solved?

Does the fretboard measure thinner (a) at the high point in the center on one end compared to the other or (b) thinner at the edge near the 20th fret compared to the edge near the nut?

(b) is normal, the arc of the fingerboard will cause the height to be thinner at the edges the wider the fingerboard is. As for (a), controlling that is something the person doing the sanding needs to control.

If the edge height is to be held constant, then the fingerboard will be thicker at the wide end if sanded to the same radius.

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Peter Havriluk

Just a natural effect of the geometry. The radius cuts farther down the farther you get from the center, so the wider end of the board loses more material at the edges.

Either switch to conical radius, or taper the center thickness to compensate, or accept it.

I think we've all gone through your thought process at one point or another. It's another one of those things that luthiers obsess over but no one else notices. I no longer worry about it.

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Steve Smith
"Music is what feelings sound like"

I just re-measured with this neck, the bass side is .011 lower at the 21st fret, the center rises .025 and the treble side rises .009. Evidently I need to up my sanding skills. I'll do some more work and see if I can't bring it all to a more consistent place. This fret board was a highly figured piece of maple, so it was an adventure thicknessing it to begin with, and I wasn't able to plane it down as thin as I would have liked.

It's good to hear that this is one of those things that isn't a make or break thing...

Just worry about getting it straight. Nothing else matters.

I radius the FB after slotting using a router and jig similar to the one below.
Mine was very simple and easy to build - much quicker, more controllable, accurate and TBH it becomes a simpler process than rubbing sanding blocks up and down a flat FB to radius it.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I made the same jig. Best thing I ever took the time to make.

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It will probably be alright.

Me too, less than a day.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

When I read your post, I get the feeling you have a problem with the sanding block, your technique, or both. Radius blocks are a very quick and flexible way to establish a simple or even a compound radius in a fingerboard.

First, do NOT use a radius block any shorter than 8”, and don’t attempt to use a flat block (possible, but much more difficult). The first sandpaper grits (P60 or P80) should be attached with double-sided tape.

Chalk your fingerboard surface and sand carefully in long strokes using BOTH arms to guide the block in a straight line. The objective is to keep the chalked middle area the same width the full length of the board. Since the board is usually tapered, you will sand more at the wider end until you establish an even width chalked area the full length. When you’re finished, the centre of the fingerboard will be the same thickness for the full length, while the edges will not.

Final sanding should be with a 24” levelling beam.

Compound radius boards are more tricky, but the same principles apply, with the levelling beam being even more important to complete blending the radii.

There are many jig designs out there to accomplish this task. Personally, I’ve never been motivated.


Sent from my iPad using Tapatalk

That's a good explanation Tim.

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Steve Smith
"Music is what feelings sound like"

What others have said plus it is always easier to do the radius before the fretboard is tapered to the neck profile. ie before gluing to the neck.

I still do mine by hand but I remove most of the material using a plane then sanding blocks. Having it sit on a flat surface and using slats to act as fences on either side it is easier to control the sanding process.

Cheers Dave

I don't know anything about guitar fretboards so when I did my arch top, I wanted a compound radius. I did it the same way I did my much smaller 5 string violin fingerboard.

I set my side height, it's 5.5 mm on a violin, I don't remember what the guitar was. Then, do some math to find the height above that the center of the radius would be at the top, and at the bottom. With a compound radius, they might not be much different, but will be more for a single radius, with the bottom taller. Add the side number to it, and taper the top of the flat board to that. For a violin, it might be about 7mm on the top, 9 or 10 at the bottom, I don't remember the numbers. The radius means the neck has to be set back a little less than 1 degree more (for a violin) to a little more than 1 degree for a viola. So you need the fingerboard to set the neck.

Then, I just plane it down until the sides are the right height. Violins have a FAR TIGHTER radius on them; 42 mm for a violin and 37 for a viola. A guitar is very subtle compared to that.

If I was smarter, I would just buy pre-shaped fingerboards and avoid that hassle and mess!

I don't think my planing worked perfectly on the guitar, they weren't THAT level after the frets were put in. But it plays fine. 2.5 - 3 mm at the 12th, with nylon strings, and if I knew it wouldn't drop, I'd make the bridge lower.

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Why be normal?

Here is a link to the simple radius jig I designed many years ago. You can see iterations of it above. It's cheap and simple and makes a single radius fretboard easy to make.

http://blackwaterriverguitars.com/Tools ... 20Jig.html

Here is a version to fit a cheap trim router.

I have used the router jig pictured for probably 16 years. It’s an excellent design for a straight radius. You need a separate sled for each radius. I do 16” on flattops and 12” on archtops so I have two.

When I final level with the neck on the guitar after the neck is shaped I use a long bar and level in line with the string runs which compounds things a little.

Sylvan Wells posted a sanding block jig a long long time ago where the fretboard is fixed to a flat board with guides on either side parallel to the center line spaced the same width as the sanding block to keep the radiused sanding block on center. I used that before I made the router jig. Worked well but it was a lot of elbow grease! Sylvan would run the board through the thickness sander with a little lift under the edges to put some facets in the board so less sanding was needed.

Without that jig it is really easy for the block to wander and get some asymmetry.

Luthier Suppliers also has a thickness sander jig that looks pretty neat.

https://www.luthiersuppliers.com/lsprod ... radius-jig

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

Very curious.
Who could share the plans for that router jig?

My current set up is a (partial) box I made exaclty the width of my sanding block.
The freboard is nailed down to it, after fretting. Then a block plane is used to hog off material. The radiused sanding block is used intermittently to check on progress until the radius is achieved.
A pencil line down the middle of the board is watched VERY carefully to make sure evenness of the board thickness is kept at all times.
It takes fifteen to twenty minutes and fifty or sixty beads of sweat to get a fingerboard radiused.

+1 on Dave above. I build 1-2 a year, and don't find this job too onerous - If I built a bunch, then the jig would be worthwhile. I double-stick tape the FB to my fret spacing template, cut the frets, and use the template to clamp the board to the bench. Then I use a plexiglass template made from a computer printed paper arc, a block plane to get it close, then a homemade 16" radius jig to quickly clean it up. Keep that pencil line down the center.
Ed M

I use the example that is shown in Somogyi's books where the fretboard is clamped to a long handle that rocks back and forth over a belt sander on a wood frame. Yea, it's impossible to describe... But, you can get a nice quick compound radius using this method. I cut fret slots in a rectangular blank, then taper and bind the fretboard before going to this jig for the compound radius. I inlay after the radius is done. Once it's on the neck I do a very small bit of sanding with a beam to make sure everything is true before doing a full finishing process along with the rest of the neck and body. I could yap more about that, but it's not relevant to this thread

If someone would like, I can grab a couple pics of this jig. But, I suspect someone has posted about it before.

I've never tried using sanding blocks, but my feelings about sanding do not permit me to try them. Yes, I hate sanding by hand that much.

As soon as I finish a few more guitars, I'm going to buy the grizzly radius sander. It's basically a fancy version of what I'm doing now, so a relatively small process change with "hopefully" more consistent results.

I can email a plan for a FB radius jig from Woodie G if you send ma a PM with your Email address.
It;s OK, found a link to Woody's post
http://luthiersforum.com/forum/viewtopic.php?f=10101&t=51761&p=681396&hilit=+radius+jig#p681396
Original design was by Mr. McClary
Mine is more simply made, involving mostly melamine board with 2 steel rods in the router carrier instead of radiused blocks on the side, so it can be used with any radius on the sliding carriage.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I just listed one of these in the classifieds.

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Good judgement comes from experience. Experience comes from poor judgement.

I don’t know what kind of bit most are using for the router sled radiusing jig but this is the one I have used for the last 14 years and being sure to do climb cuts it has worked well. I will still occasionally get a very small chip out on a fret slot but pretty minor. Leaves a very smooth finish. I actually need a new one.

https://www.acmetools.com/shop/tools/freud-99-026#


I have been doing it in one pass starting with the bit just touching the centerline but before routing move the cradle to each edge with the bit just clearing and be sure the radius is symmetrical. If not you can shim the carriage with tape.

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

I have always used a straight bit with mine and start at top dead center where the least amount of wood is removed. I take a pass down the length, index the carriage down a bit, and take another pass backward, etc. This creates facets on the board and then by the time you are done you are have a nice radius to be cleaned up with abrasive. It will chip out on the outside edge occasionally, so this really should be done before tapering the fretboard. That way, the chip out is on the waste. A straight bit should just leave swirls to sand out if it is sharp and the jig is well made.

The smaller version I posted a picture of works, but isn't as robust as my original one made out of 3/4" plywood. Still it's nice to dedicate a router to it and it stores away pretty easily. I used some shelving stock from lowes and the double sided tape causes the thin melamine laminate to delaminate. I'd choose something else next time for the flat surface for it to ride on.

Here's a link to a way I've been radiusing fingerboards with an inline pneumatic sander. I'm now using a much longer radius block and check often with a straight edge and finish up sanding with a beam on the string paths. viewtopic.php?f=10101&t=50427.