Top nut for any string instrument (bass, guitar)

Summary

Well this escalated quickly with regards to number of hours spent...
But now I'm finally happy with the result.

• This top nut uses true fretboard radius, default is set to 12" but this can be changed as everything else.
• Enter dimensions of nut, number of strings, distance from nut edge to outmost strings, the desired string height and let the magic begin.
• Each string slot uses the string diameter and each string can be individually adjusted.
• All slots can now also be angled in any number of degrees.
• Paired strings layout handled too (like a 12-stringed guitar)
• Proportional or equal spacing rule can be choosen. I recommend proportional rule.
• Paired strings are also layout using proportional rule if that rule is choosen. This means that first the even strings are positioned proportionally and then odd strings are positioned so that the open space between two paired strings are equal.
• Read about what proportional spacing means here for instance: http://www.projectguitar.com/tutorials/instrument-building/equal-vs-proportional-string-spacing-r15/

The customizer here in MarkerWorld works fine so go ahead and use it. If you rather want to work in OpenSCAD just download the file and change your parameters.
 

2022-07-18 Improved chamferCorner function, increased $fn from 80 to 160, revert if too much for your computer
2020-05-01 New algorithm altogether that uses proportional spacing rule. Added possibility to adjust position of each string too.
2020-04-25 Corrected algorithm for paired strings (read 12-stringed guitar).
2020-03-27 Added option to make v-shaped string slots (default and recommended) or straight slots
2020-01-24 Added option to group strings in pairs, 12-strings are now handled too. Comment if its not working as it should.
2018-08-24 Now works in Customizer after removing letter ö from my last name inside a comment...
2018-08-07: Added parameter stringAngle to angle string slots

Print Settings

Printer: 

Tronxy PM802

Rafts: 

No

Supports: 

Doesn't Matter

Resolution: 

0.15

Infill: 

at least 50%

Filament: Any but preferably something durable
 

Notes: 

Since this is a quite small part infill might very well be set to 100% for better strength.
I have printed in white PLA with 50% infill and it seems to work fine.

Important to note that the edgeDistances you enter are measured to the outer edge of the outermost strings. Not the center of the strings as before.

Post-Printing

Trimming

Elephant foot is a problem here since the nut might not fit due to this. So it needs to be trimmed with a knife. Also the string grooves might need some fixing.

How I Designed This

Step 1. Make a big torus with nut radius

Torus with elliptic cross section where radial size is nut height2 and axial size is nut length2.

Main torus with selected radius

Step 2. Subtract first big block to get the height

Construct height of nut by cutting it in the middle.

Step 3. Time to trim the sides

Subtract a block to trim one side

Step 4. Subtract other side

Step 5. Remove the evil twin at the back...

Now nut has correct height and width, the only problem is that we have two of them so we remove one

Step 6. Split in half

To get the correct length of the nut (string wise) we need to cut it in half again.

Step 7. Now perform all subtractions for real

Now we have the basic nut but with sharp edges and no slots.

Step 8. Chamfer corners

Each corner is chamfered individually with regards to the distance from the edge of the nut to the outermost string.

Step 9. Add string slots

These can be v-shaped or just straight slots. Also choose from proportional spacing or qual spacing. This example uses proportional spacing.

And we're done!

Finished nut with proportionally spaced V-shaped slots