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Hi all. I am working on my first acoustic builds (two at once) and i can’t find any information to confirm I have my fretboard/neck taper correct. So, I’m looking for a bit of help which will be greatly appreciated. My build details are below. How do I calculate the width of the fretboard at the twelfth fret to get my taper correct?

1. Slope dread with 25.4” scale, 1 11/16” nut and 2 1/8” string spacing at the bridge.

2. 000 12 fret with 25.4” scale, 1 3/4” nut and 2 3/16” string spacing at the bridge.

I could probably figure out a way to calculate it, but it's easier for me to draw it out. Either on paper or with a CAD system.

A line for the edge of the nut. The bridge is another line, your scale length plus compensation away. Mark your string spacing at the bridge and string spacing at the nut. Sketch in the strings. Mark a line at the body joint.

You can also measure existing guitars you have, or parts you have - I see these are your first builds though.

Calculating the fingerboard shape
The common way to determine the fretboard shape is to make a drawing on a large sheet of paper. Here is annother approach with the help of a calculator or a spreadsheet program.

Two measurements determine the width of the fretboard: The nut width X and Y the string spacing at the saddle (B) plus two times d ("d" is the distance from the outer strings to the fingerboard edge which should be equal along the entire fretboard length).


width = X + [( L ( Y - X ) ] / S


D ... distance of outer strings to fingerboard edge
X ... nut width (A + 2d)
Y ... bridge stringspread (B) + 2d
L ... distance from nut
S ... scale length

With the formula shown above you can for instance calculate the width at the 23rd fret (the end of the fretboard on a 22-frets guitar) which gives you all the necessary data for drawing the fingerboard outline:

For instance:

Width at nut (X) = 42mm (1-5/8")

Distance nut to 23rd fret (L) = 462.14mm (18.195")

d = 3.5mm (1/8")

String spread at the bridge (B) = 54mm (2-1/8")

Y = B + 2d

Width at 23rd fret = 55.97mm (2.203")

Tried to put it in standard notation, but the software rearranges things. There are calculators on the internet. I pulled this online.

Here's the entire Calc.

http://buildyourguitar.com/resources/tips/c_layout.htm

Diane Kauffmds wrote: ↑Wed Feb 22, 2023 12:00 pm width = X + [( L ( Y - X ) ] / S



D distance of outer strings to edge of board
X nut width
Y string spread on bridge
L distance from nut
S scale length

Tried to put it in standard notation, but the software rearranges things. There are calculators on the internet. I pulled this online.

Here's the entire Calc.

http://buildyourguitar.com/resources/tips/c_layout.htm

Your formula is Missing D, the string to board edge distance you list?

Edit - Y should be string spread on bridge plus 2 times D

Yes. That's why I put the link.

Man. Math hurts. I just make the nut either 1 3/4” or 1 11/16th. Then make the 12th fret 2 1/8” or 2 1/4” depending on my design for the build. My string spacing on bridge is either 2 1/8” or 2.312” based on a little bridge template I got from Stewmac. This taper allows for ample spacing outside the strings.

I draw it in a CAD program.
Width of nut -- typically 1-3/4"
Minus 1/8" on each side for locations of 1st and 6th strings
Distance to bridge, typically 25.4"
Distance between bridge pins 1 and 6, typically 2-1/4"
Then I draw lines between the locations of the 1st and 6th strings at the nut and the 1st and 6th bridge pins (pink lines in drawing). Then I offset those lines by 1/8" outward, which gives the fingerboard profile (taper).
There are probably easier ways to do it, but I can follow this and not get confused.

Ok…time to get out my calculator! I very much appreciate the help. I do think I’ll wait until I’ve had my coffee tomorrow to crunch the numbers.

I've read that:

the width of the neck at 12th fret = string spacing on bridge.

I think it's meant as a guide but not chiseled in stone.

Diane Kauffmds wrote: ↑Thu Feb 23, 2023 8:36 am I've read that:

the width of the neck at 12th fret = string spacing on bridge.

I think it's meant as a guide but not chiseled in stone.

It comes out within a hair of this rule of thumb. Thanks for all the help everyone.