Guitar fret slot positioning

I’m relatively new to python, and have started learning for the above reason.

I want to be able to model guitar necks (and then cut on a CNC router) relatively quickly, but most of all accurately (which is where the scripting comes in)

The fret slot distances use a constant (17.81…) divided by the string length which is repeated 22+ times with an ever shortening string length. Online I have found a python version of a trusted calculator and was wondering if anyone had tips/ideas on connecting the mathematics in said calculator to something like rs.addpoint (or addline) to create an array of points/lines in the correct spacing.

Below is the fret calculator script.

# From Stewmac
# To calculate the scale length for stringed instruments

# Notes on fret layout
# The most accurate way to lay out your scale is making all measurements
# from the nut (using the "fret to fret" distance only to confirm your layout).
# Laying out frets only by measuring fret to fret will compound error.
# For example, if you're laying out frets by marking with a scribe and your
# accuracy is plus or minus 2 millimeters, you could be off by as much as
# 24 millimeters at the 12th fret.

# Measurements are given from the end of the fingerboard (face of the nut)
# to the center of a fret slot.

Im = ''
const = 17.817 # Do not change this

def fretCal(ScaleLength, nofret):
    '''(number, number)-> float
    Calculates the fret positions for any stringed instrument
    Given 'Scale length', 'number of frets' in inches or mm
    >>> fretCal(19, 18)
    Fret 1 from nut 1.066 inches
    Fret 2 from nut 2.073 inches
    >>> fretCal(635, 22)
    Fret 1 from nut 35.64 mm
    Fret 2 from nut 69.28 mm
    if ScaleLength < 99:
        scale = ScaleLength
        Im = 'inches'
    if ScaleLength > 100:
        scale = ScaleLength
        Im = 'mm'

    for i in range(1, nofret +1):
        ScaleLength = ScaleLength - (ScaleLength / const)
        print('Fret', i, 'from nut',round(scale - ScaleLength, 3),Im)


Hope someone can help!


Hi Oliver,

Perhaps I don’t fully understand your project. If your goal is just to quickly and accurately create a set of points or lines in Rhino spaced accurately for fret scales one simple way is to generate the series one time for a scale length of 1 and then use “scale” to the desired length. Really no need to recalculate every fret location each time. But perhaps you have something more elegant and automated in mind.

It’s all there- with minor mods it does what you want. I’ve enclosed the working version. (2.1 KB)