CAD Fretboard Builder

[Jeff Siddall]

For one of my bass projects I needed a multiscale, compound radius fretboard and decided I would try to build one with a CNC. First I needed to create a 3D model and decided it would be useful to automate this with a FreeCAD Fretboard Builder Macro. I had posted about this in another thread but figured it probably deserved its own thread to make it easier to find.

The macro is effectively FretFind3D. In addition to handling multiscale, it also has the option to construct either a zero fret or a nut slot, add string margins with the option to use different amounts on each side of the fretboard, plus several other improvements to usability (ex:configurable perpendicular fret).

Here is a screenshot of two bass fretboards, one with a nut slot and one with a zero fret:

and a link for anyone interested in trying it:

Macro Guitar fretboard - FreeCAD Documentation

As always, any feedback is welcome!

 

[TrustRod]

That looks great. The only slight critique I have is using the bridge radius for the compound radius. You have nut & bridge as the choice and I think more people would be familiar with using nut & 24th fret.

That said, great tool and thanks for sharing it for free. This will be very useful for those struggling with multi scale layouts.

 

[Jeff Siddall]

That looks great. The only slight critique I have is using the bridge radius for the compound radius. You have nut & bridge as the choice and I think more people would be familiar with using nut & 24th fret.

That said, great tool and thanks for sharing it for free. This will be very useful for those struggling with multi scale layouts.

Thanks!

I though about the right way to specify the two radii and concluded the only universal way is to use the two string suspension points (nut and bridge). This isn't uncommon in the industry:

Prima Artist

"Fingerboard radius – compound, 7-1/2” (at the nut) to 25” (at the bridge)"​

Using the bridge radius is also tangible as you can use a radius gauge to check what your bridge will look like when accommodating the desired radius.

Then there is the problem that not all boards have the same number of frets. You can't ask for the 24th fret if the board will only have 20!

Building the fretboard all the way to the bridge in CAD also solves a logistical problem because the fretboard always needs to extend beyond the last fret, yet there is no easy math to figure out exactly what that radius should be there (and it's not linear).

The best I can suggest, for anyone who doesn't know the desired radius at the bridge, is to make an estimate, build the board in CAD, then check the radius at the desired fret (21, 24 etc).

 

[TrustRod]

Well that all makes sense And it does change linearly (I just double checked) so if you use 10 nut & 16 bridge it comes out to 13 at the 12th fret and 14.5 at the 24th.

I don't think I've ever seen it listed as the bridge radius before.

 

[allexcosta]

I don't think I've ever seen it listed as the bridge radius before.

It's common.

 

[Beej]

It's common.

Examples? I've not seen it before. Usually, amongst builders anyway, it's nut to 24th fret. If there are less or more frets, its extrapolated. The radius at the bridge would just push more calculations - first I'd need to estimate the bridge radius in order to work out the desired radius at the 24th fret.

CNC aside, most builder's jigs cut the radius from one end of the board to the other. I don't put a board in my jig and set 9" at the nut and 20" at the bridge, i place it roughly at the 24th fret. My jig will only accommodate about a 28 fret board at 34" scale. Most jigs I've seen do it similarly.

Might be worth building in the additional ability to set the radius at the 24th fret and have the bridge radius "fall into line"

 

[two fingers]

Smart people are.... like.... smart.... and junk.

Seriously, cool tool.

 

[Jeff Siddall]

Well that all makes sense And it does change linearly (I just double checked) so if you use 10 nut & 16 bridge it comes out to 13 at the 12th fret and 14.5 at the 24th.

I don't think I've ever seen it listed as the bridge radius before.

Hmmm... yeah, thinking about this again, you are right. Radius is linear, it's the thickness of the edge of the board that is not necessarily.

So I might just add a note explaining how to calculate the radius at any given position along the board. It's easy with the 24th fret: (3/4*(bridge-nut))+nut, or rewritten, the bridge is (4/3*(24th-nut)+nut

EDIT: Having considered this a bit more, I am beginning to think it might be better to offer the option of having the fretboard builder calculate the ideal bridge radius given the nut and bridge string spacing. Anything other than that will cause an uneven string height across the fretboard.

The math basically involves figuring out the apex of the strings given their angle (i.e.: where the strings would cross if extended past the nut), which can be determined by the string spacing at the bridge and nut. With the apex known (which is where r=0 for a cone) and the known radius at the nut, the radius of the cone at the bridge can be determined.

Interestingly, I ran the numbers for the Dingwall listed above and the ideal bridge radius is actually around 14" which is a significant difference from actual.

That makes me wonder why builders don't seem to use the ideal conical section shaped fretboard. Hmmm...

I might post that question to another related thread I came across previously.

 

[allexcosta]

Examples? I've not seen it before.

I remember the guys from Fodera years ago mentioning 9.5 on nut and 20 on bridge for the 4 stringers or something like that. End of fretboard would be close to 16.

I'd say most mention nut and end of fretboard, but have seen nut and bridge on a few occasions.

Just found this, actually:

Sheldon Dingwall – Our compound radius starts out at 7.5” at the nut. The string taper determines how much of a compound variance is needed. More taper needs a more variance. Our basses typically flatten out to about 25” at the bridge. 7.5” to 25” sounds radical, but it feels pretty natural, and there’s no arguing with physics.

From here:

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[Beej]

I remember the guys from Fodera years ago mentioning 9.5 on nut and 20 on bridge for the 4 stringers or something like that. End of fretboard would be close to 16.

I'd say most mention nut and end of fretboard, but have seen nut and bridge on a few occasions.

Just found this, actually:

Sheldon Dingwall – Our compound radius starts out at 7.5” at the nut. The string taper determines how much of a compound variance is needed. More taper needs a more variance. Our basses typically flatten out to about 25” at the bridge. 7.5” to 25” sounds radical, but it feels pretty natural, and there’s no arguing with physics.

From here:

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Thanks Allex, it's nice to read that again! I have seen some examples, but it seemed to me that a bridge radius being discussed was the exception rather than the rule, mostly because when we're talking about a fretboard radius, it's easy to talk just about the fretboard, as that's typically what's being worked on, or planned for. The idea that it's common was what surprised me.

 

[Jeff Siddall]

I remember the guys from Fodera years ago mentioning 9.5 on nut and 20 on bridge for the 4 stringers or something like that. End of fretboard would be close to 16.

I'd say most mention nut and end of fretboard, but have seen nut and bridge on a few occasions.

Just found this, actually:

Sheldon Dingwall – Our compound radius starts out at 7.5” at the nut. The string taper determines how much of a compound variance is needed. More taper needs a more variance. Our basses typically flatten out to about 25” at the bridge. 7.5” to 25” sounds radical, but it feels pretty natural, and there’s no arguing with physics.

From here:

Link Removed

I would agree, bridge is not the most common specification, but neither is 24th fret, 21st fret etc. because different basses have different amounts of strings. What is definitely not commonly used is the string spacing at the 21st, 24th fret etc., and since that is one of the determining factors of the ideal radius in a compound radius board there is always going to be some uncommon bit of information. Standardizing on bridge radius makes the most sense to me since almost everyone already specifies bridge string spacing.

Having said all that, I am still scratching my head about Dingwall. I totally agree with what he says about "The string taper determines how much of a compound variance is needed". I looked at the math some more and it works out that the ratio of the string spacings at nut and bridge must match the ratio of the radii for a conical board. So in the case of Dingwall, where the bridge spacing is 18 mm (5 string), and the nut spacing is about 9.4 mm (45.5 nut width minus an assumed 8 mm of string width and overhang) the 7.5" nut radius requires a 14.4" bridge radius. But then he goes on to say they use a 25" bridge radius.

I guess the great thing about building my own is I don't have to do what anyone else is doing, though I would certainly like to understand why different people do things differently.

 

[TrustRod]

While unfamiliar to me I do agree using bridge radius makes the most sense, but it's not the most user friendly as you have to ask a musician to do math For the CAD builder could you leave it as bridge but simply show what that works out to so it can display what it will be for 20 & 24? Or maybe you put in a fret and it gives you the number. Or even let the user choose where the second radius is placed and let their computer do the math and compute the radius at the bridge. So you could say 16" at 22nd and it will compute the difference between nut and chosen position and then multiply a few things. Wow that got complex, using bridge and then simply displaying for another location wouldn't be too bad.

I'm confused as to what string spacing has to do with radius though. If I change the spacing at the nut or bridge it doesn't change the radius, only how much of the cone I'm getting. In my CAD program (Fusion 360) I simply make a cone with 2 circles placed wherever I choose and then use that to cut the surface of the fretboard. String spacing + overhang decides the outline of the board and these two options don't affect each other. Fusion360 will extend the cone in either direction so there's no problem going past the place the radius was placed.

 

[TrustRod]

Just had a peek at the Warmoth site, they use nut and heel which is how I've always looked at it. I assume when they do a 24 fret overhang on a Fender style they ignore the extra frets.

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[TrustRod]

To throw another monkey wrench on the fire, I've been using 16" non compound on 5 string basses. It's pretty close to flat. Since I learned on classical/Spanish guitar which is flat, as are banjos and most basses over 6 strings, I'm considering trying flat on a 5 string. I've seen a few people do this on basses and am tempted to try it on something I could radius and refret if I hate it.

 

[Jeff Siddall]

While unfamiliar to me I do agree using bridge radius makes the most sense, but it's not the most user friendly as you have to ask a musician to do math

Yeah, I see your point. I will look into the option of entering either last fret or bridge.

I'm confused as to what string spacing has to do with radius though. If I change the spacing at the nut or bridge it doesn't change the radius, only how much of the cone I'm getting. In my CAD program (Fusion 360) I simply make a cone with 2 circles placed wherever I choose and then use that to cut the surface of the fretboard. String spacing + overhang decides the outline of the board and these two options don't affect each other. Fusion360 will extend the cone in either direction so there's no problem going past the place the radius was placed.

It's not that you can't make a cone of whatever radius, it's that if your string spacing ratio doesn't match the radius radio then the strings won't be the same height above the fingerboard all the way along the neck. See this thread where I show an example of how the height varies:
For anyone who has tried to visualize a string path along a fingerboard...

Also, I found this link that also sorta explains it:
[This invalid link has been removed]

 

[TrustRod]

Thanks, I can see it now

But this also means all non compound boards are lightly flawed, or not achieving their full potential.

I've always heard of a compound radius being used to leave a smaller radius by the nut to make chording easier and flatter up the neck to make bending easier without fretting out. Which is the reason Warmoth gives. And a bazillion Tele players.

Now that I understand I'm going to have to use it or simply go flat.

 

[Jeff Siddall]

Thanks, I can see it now

But this also means all non compound boards are lightly flawed, or not achieving their full potential.

I've always heard of a compound radius being used to leave a smaller radius by the nut to make chording easier and flatter up the neck to make bending easier without fretting out. Which is the reason Warmoth gives. And a bazillion Tele players.

Now that I understand I'm going to have to use it or simply go flat.

Yes, correct, almost all basses don't have strings that following a ruled surface. So even a neck with perfectly installed frets still needs a fret level -- to fix the incorrectly shaped board!

Bottom line is that all fingerboards that aren't flat and don't have parallel strings should be compound radiused. But, of course, you can fix slightly imperfectly shaped boards with a fret level, which has been the de-facto solution for as long as the electric bass has been around.