minimum amount of wood lost when sanding radius info?

VegasCustom

VegasCustom

May 10, 2023
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Vegas
#1
Hey everyone,
Is there a chart or link somewhere for info on the minimum amount of wood lost on the edges of fretboard when sanding various radius?
I can figure it out tomorrow but I'm wondering if it exists now to save some time. Thank you!!
 
#2
VegasCustom said:
Hey everyone,
Is there a chart or link somewhere for info on the minimum amount of wood lost on the edges of fretboard when sanding various radius?
I can figure it out tomorrow but I'm wondering if it exists now to save some time. Thank you!!
Click to expand...

I've always drawn it out in CAD, or full size in pencil, using a radius gauge. But it's just geometry. You could work out the equation and make up a spreadsheet if you wanted to.
 
#3
It’s actually more complex than it seems. As the neck gets wider, the edges are farther from the center highpoint of the board, so lower on the arc of that radius. It’s subtle, but the edges get thinner as you climb the neck unless you are doing a compound radius. The math of this escapes me, but Autocad does it for me. I have yet to try compound radius, haven’t felt the need. I have found it very difficult to get consistent results by hand using a radius sanding block so I'm building a radius jig for my router for the next one. In practice that gradual reduction in edge thickness is not noticeable visually, but it's measurable with a dial caliper.
 
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#4
Get the widths of the neck at opposite ends of the fretboard. Those values are the chords (width of arc) that you will plug into this calculator,* adjusting units as needed. All you need is that value and the fretboard radius, the calculator will find the rest for you. The value you're interested in is Height of the arc.

The height of the arc defines how much lower the edge of the fretboard is relative to the middle of the fretboard.

Let's say I'm building a weirdly-shaped five-string bass... given a 1.75" nut width and 3" heel width and 12" fretboard radius, the arc's height (difference between edge and middle of fretboard) will be about 0.032" at the nut and about 0.094" at the heel.

*(it works fine but has a weird bug: produces two rows of results. First row is correct, second row is not. There are other online calculators that should be less early-2000s in design, in case you don't like using this one.)
 
#5
I agree with the suggestion to CAD. It's easy to see the cross-sectional design of the neck and how the neck profile can be resolved, particularly if creating a profile by cutting facets along each side.

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#7
Not everyone has access to Autocad, it's a very expensive software with a lot of bloatware and bells and whistles I never use, but there are a lot of good drawing programs out there for far less money. Even ACAD LT is more than powerful enough for making working drawings. If you (the OP) are serious about building basses, it would be absolutely worth it to invest in one. I draw EVERYTHING out in CAD before I ever touch a piece of wood, and .001" can matter on a bass.
 
#9
Yes, as an example. the fingerboards on my Scroll Basses are 34" scale, 1 11/16" at the nut x 2 1/2" at the heel, and 7.25" radius. I cut them to 0.240" thick at the heel x 0.220" at the nut, measured at the center. This formula makes the edge approximately even thickness all the way down.

I worked out those thickness numbers by experimenting in my radiusing fixture. I first cut the radius with the thickness set equal at both ends, and I found that 0.240" thick at the heel gave me an edge thickness at the heel, which looked nice. Then I raised up the nut end of the neck in the fixture, a little bit at a time, and made more cuts until the edge thickness looked right, about even down the whole length. I measured the resulting thickness at the nut, and found it to be 0.220". So, I adopted that as my standard fingerboard thickness taper: 0.220" at the nut x 0.240" at the heel. And I've made up a setting gauge that I use to adjust my necks in my radiusing fixture, so they always come out to that thickness taper.

Over many years and necks, I've found that the 0.020" thickness taper number is also about right for most other bass fingerboard dimensions; width, thickness, radius. I normally set up to cut the thickness 0.020" thinner at the nut than at the heel.

But I don't think this is what VegasCustom was asking about.
 
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#10
Back to the OP's question, if you start out with a 1/4" thick off the shelf board, in theory you are taking off very little wood to radius it, ideally close to 0 at the center, and only what's needed to achieve the radius at the edges. In practice you'd take off slightly more than zero at the center to avoid a flat spot, and any final sanding will take off a bit more, but I can't see it amounting to more than what, 1/16"? I've taken off more than I wanted to doing it by hand, with a radius sanding block, chasing errors in my sanding technique.
 
#11
Gilmourisgod said:
Back to the OP's question, if you start out with a 1/4" thick off the shelf board, in theory you are taking off very little wood to radius it, ideally close to 0 at the center, and only what's needed to achieve the radius at the edges. In practice you'd take off slightly more than zero at the center to avoid a flat spot, and any final sanding will take off a bit more, but I can't see it amounting to more than what, 1/16"? I've taken off more than I wanted to doing it by hand, with a radius sanding block, chasing errors in my sanding technique.
Click to expand...
Question:
"Is there a chart or link somewhere for info on the minimum amount of wood lost on the edges of fretboard when sanding various radius?"

Not that I know of. ;)
 
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#12
Here's a calculator that will tell you, if you give it the radius and the width of the fingerboard (as "chord length")

No endorsement, there are probably others, or you could likely cook up a spreadsheet if it made you happy.

www.omnicalculator.com

Segment Area Calculator

With our segment area calculator you can find area of a segment given the central angle or segment height.
www.omnicalculator.com www.omnicalculator.com

Ignore the segment area it purports to be a calculator for, the "minimum amount taken off the edges" number you want is precisely the "height" result if given radius and chord length. Note that you can change it to mm if more convenient, or stick with inches if that's more convenient, or mix them up if you like to miss Mars with your orbiter.
 
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