Fretboard Radius question

[Jad20540]

I messed up my first radius job, turned out to be a lot harder than I thought. The fretboard on the nut end became radiused a lot quicker than the saddle end and the edges (sides) of the nut became considerably thinner than the centre.

I bought another fretboard and am having a second go. I am using a 16’’ radius block. My question is: On the nut and saddle ends, approximately how much thinner should the edges be in comparison to the centre point?

Thanks for any feedback.

[mirwa]

Use a straight bar as well to keep your work in check.

Straight bar maintains an even thickness end to end, radius cauls simply establishes a radius along that length

Steve

[Jad20540]

Thanks Steve .. but doesn’t radiusing make the edges of the board thinner than the centre? Aren’t you taking more out from the edges when using a radiusing beam? If yes, I am interested to know by how much should the sides be thinner to the centre?

[mirwa]

The radius is the radius, you pencil your board and then sand it until all the pencil marks are gone, the centre of the board will be thicker than the sides of the board, the difference in heights is subjective to the chosen radius, a well sanded board will have even sides.

The flat beam ensures the thickness is maintained front to rear (nut to saddle)

Steve

[Jad20540]

Got it, thanks

[redir]

It makes sense that the edges will be thinner then the sides right? That's why you need to cut the fret slots deep enough to account for this, or cut them again after putting the radius on.

It also makes sense that you would sand the nut end faster too. So good technique when using radius blocks is to focus on the saddle end a bit more and also take sanding strokes from one side then rotate the piece 180deg and sand it from the other side. That way you don't create a systematic error based on your right or left handedness so to speak. You will have a tendency to sand harder on one edge so rotating it transfers that tendency to the other side.

The sanding beam is the way to go. There was just a thread on this topic last weak I believe. You can use a jointing plane with sand paper (as long as you know it's dead flat) among other things, I think one person used a simple piece of MDF which should work well. If you plan on making more guitars then I think having a nice steel beam like Stew Mac sells is best.

[charles Tauber]

Originally Posted by Jad20540

I bought another fretboard and am having a second go. I am using a 16’’ radius block. My question is: On the nut and saddle ends, approximately how much thinner should the edges be in comparison to the centre point?

Between 1/32" and 1/16", roughly. It is easy enough to calculate, if you want to, but not much reason to.

Alternatively, put your radius block on edge. Mark a centre line on the edge of the block to use as a reference. Use a centre-finding ruler - or equivalent - and mark on the edge of the block where the 16" radius intersects with the width of your fingerboard at the nut. Repeat for the width of your fingerboard at the sound hole end. Measure the vertical distance between the two marks on the edge of your radius block and that's the amount by which the edges of the fingerboard will vary.

Alternatively alternative, find a guitar with a 16" radius fingerboard. Measure the thickness of the fingerboard edges at nut and sound hole.


If you have the skills, you can remove much of the waste fingerboard with a hand plane, then finish up with the sanding beam and radius block. (I don't use - or have need of - radius blocks.)

[Howard Klepper]

I've never used a radius block. I don't see the need for it. I also don't see how you can avoid creating a radius smaller than the radius of the block, or how radius blocks are supposed to work if you are doing a compound radius (which I always do unless it's a vintage restoration). I use a flat hard rubber block and keep checking with radius gauges.

After I got some experience, I began to first do some roughing out on a belt sander, stopping short of the final radius, but don't do that if you are a beginner.

[Rodger Knox]

Originally Posted by mirwa

a well sanded board will have even sides.

Steve

With a tapered neck, the sides of the fretboard will only be even if there is a compound radius. A single radius will have an even taper, with the nut end being a bit wider/thicker at the edge, assuming a uniform thickness at the center.

[murrmac123]

Originally Posted by Rodger Knox

With a tapered neck, the sides of the fretboard will only be even if there is a compound radius. A single radius will have an even taper, with the nut end being a bit wider/thicker at the edge, assuming a uniform thickness at the center.

+1.

The only way you can have a constant width at the fretboard edge and at the same time have a constant (non-compound ) fretboard radius is if the thickness at the center of the fretboard blank increases incrementally from the nut end to the soundhole end.

Constant fretboard thickness +constant fretboard radius + constant edge thickness is a physical and mathematical impossibility.

Unless, of course, the fretboard is also a constant width along its length .... but when has that ever happened ?

[mirwa]

Originally Posted by Rodger Knox

With a tapered neck, the sides of the fretboard will only be even if there is a compound radius. A single radius will have an even taper, with the nut end being a bit wider/thicker at the edge, assuming a uniform thickness at the center.

I typically agree with your Rodger, technically you are correct, however I think for the lay person they would never spot that side taper. The difference your referring to is 0.4mm over a 400mm length, or for imperial minded 1/64 deviation over 18 inch fretboard length

Steve

[Rodger Knox]

Originally Posted by mirwa

I typically agree with your Rodger, technically you are correct, however I think for the lay person they would never spot that side taper. The difference your referring to is 0.4mm over a 400mm length, or for imperial minded 1/64 deviation over 18 inch fretboard length

Steve

We do a lot of hair-splitting around here, I didn't bother to calculate anything. I started to mention it probably wasn't much.

I do most of my fretboard radiusing on the drum sander using a technique in Bob Benedito's book that I modified slightly. After I initially cut the fret slots while the board is still square, I cut the taper into the neck and save the offcuts. I use those as a shim to square up the fretboard in a carrier fixture for the drum sander.

There's an angle on the bottom of the fixture, so it sands an angle on the edge of the fretboard. Flip the board around, swap sides with the offcuts/shim, and run it through for the other side.

That gives you three facets on the fretboard, with the outside facets a uniform width and the inside facet tapering to be narrower at the nut. I round off the boundaries of the facets with a radius block, and check the string path of each string with a straightedge.

I sand in the desired relief for each string along the string paths, recut the fret slots, and install the frets.

I know it's a compound radius, but I don't know(or care) exactly what they are.

[JonWint]

I measured a half-dozen Martin boards that I have. The center-of-the-board thickness increases from fret zero to fret 18, 19 or whatever at the bridge-end (BE) of the board. The board edge thicknesses reduced when moving to the BE.

The side taper is much less than the center increase; in a ratio of about 1:4. The side taper is mostly not noticeable to the eye.

[Slight Return]

I use radius blocks whether I'm doing a compound or straight radius. I also use a 16" sanding beam.

A good straightedge and a set of radius gauges makes quick work of this job. On my 12 string I actually prefer a 7.25" to 9.5" compound radius, and I accomplished this with short radius blocks and a 16" beam.

I use the 16" sanding beam to get everything perfectly flat first, then I use the radius blocks where desired. I'm constantly checking with the straightedge and radius gauges to make sure everything is as even as possible. Sometimes when I'm doing custom radii (like 6") that I don't have a block for I do it by hand, but for me, the radius blocks make the job much faster and easier.

Just gotta be careful and test often with the radius gauges and straightedge and you'll be fine.

If everything is lining up straight and even with the straightedge, with no gaps anywhere (measured along all the string paths), and your radius gauges are getting perfect readings up and down the whole board too, you're good to go.

Shining a good flashlight behind your straightedge as it's laying on the board is a great way to do accurate work. Good reason to have a thick straightedge too: it can stand on the board on its own.

Anywhere you see light coming through has gotta be touched up. There is some leeway here and extremely minute imperfections will make no actual difference. But you do want it as close to perfectly even as possible.