Fretboard radiusing question

[6Hz]

My first build's coming along. I've got the fretboard glued on, made myself
a 12" radiused sanding block, and I'm applying it to the the fretboard.

I'm running into an unforeseen question which if I could do geometry in
my head better I should have foreseen. At the moment when the last flat
parts have been sanded round from nut to bridge, there's a lot more wood
taken off from the bridge end. So even though the thickness at the centerline
of the fretboard is the same all along its length, the edge thickness is
much less at the bridge end.

So the question is, do I sand more at the nut end to make the edges
even? Or leave it with the uniform centerline thickness?

In case it's not clear what I'm talking about, here's an exaggerated
diagram of the problem -- radiused fretboard oriented nut-end up.
Notice because of the neck taper, the edge profile is thicker near
the nut.

On the bass itself of course, it's much less pronounced. But I haven't
seen anything suggesting which way to handle it.

Thanks!
--six

[DSB1]

Originally Posted by 6Hz

So the question is, do I sand more at the nut end to make the edges
even? Or leave it with the uniform centerline thickness?

No. This is normal. If you want a uniform edge on your fretboard then use a compound radius or no radius.

[bowthing]

Ah! Read up on conical vs. cylindrical fretboard radii (just do a web search). I am making a jig to do both kinds, since I am at the fingerboard stage of my project.

The equation for calculating the radii is just the pythagorean theorum:

R = t/2 + w^2/8t,

where t is the height of the radiused portion, w is the fretboard width, and R is the radius. Start with the radius you want at one end (width) to calculate t, and then find R at the other end.

Making the conical radius is another story, which is why I am making a fixture....

[SDB Guitars]

If you use a flat sanding block (it can be done... a really sharp block plane will work too) and sand or plane with the lay of the strings, you can do a compound radius (conical) fretboard... if you make the edge taper the same all the way down the board, and at the bridge end you are at 12" radius, your nut will be about 8" or so, I'd guess, depending on your nut width...

[6Hz]

Thanks! This was really helpful.

I'd looked at compound radiusing while I was planning this thing and
I decided against it for a couple of reasons: I'm not a good enough player
that it's going to make much of a difference, and it looked like the sort
of hard thing you save for a second or third build ...

But the problem I was having was with a cylindrical section. There's
a (wrong, I now understand) way to shape a single-radius fretboard
so that the edge profile is even all down the neck. Here's another
illustration -- it requires more sanding at the nut than at the bridge
and results in a board that's a lot thicker at the bridge end:

[pilotjones]

Yup. And if you compare your last illustration to the first, you'll see that the last is equivalent to doing the first, and then removing a wedge from the backside.

[Arx]

the warmoth gecko neck that I have has a consistent edge. The centreline is thicker at the body by quite a visible margin. As long as it ends up at the right angle in relation to the body, I don't think it much matters. Unless you're going to do a compound radius, or a perfectly rectangular board, that's just how it'll be.

EDIT: Actually, I just double checked, and it looks like they may have split the difference. The edge is slightly thinner at the bridge end, and appears slightly thicker in the middle. This is the wide version though, so it probably doesn't have as much taper as the medium, or some other necks that are narrow at the nut in comparison to the body end of the neck.