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Multi Scale Layout?


jer7440
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I want to make sure I have this straight in my brain before I get to far on this guitar design I'm working on. I'm thinking along the lines of a multiscale with a 27" scale on the low side and a 25 on the high. I made the 7th fret the common fret between the two scales. So I took the fret positions from the 27" scale and the 25" scale and I laid them on the fretboard with the 7th fret being horizontal or perpendicular to the center line of the neck. Then I connected the first fret of one scale to the first fret of the other...creating the "fan". Does this sound about right?

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yeah, you need to decide on nut and end of fretboard width so you know the string paths of your 27" and 25" strings

here is what i do, no CAD just a pencil and ruler!!:

*first things first, draw your centre line

* mark on the nut position, then using the shorter scale length mark on the nut, 7th fret and 22nd fret positions

* draw a line perpendicular to the scale length at these points

* mark on the width of the fretboard at the nut and 22 fret lines

I go with standard spacing so i would make the nut about 42-44mm and the end of fretboard about 56mm

*you can now draw the fretboard edges like you would on a standard fretboard.. but extend the lines a bit past your nut and 22nd fret lines

* next i would draw the outer two strings into position about 3mm in from the edge

* now measure back along the string line from the 7th fret to the nut position for each scale length and join the dots to give your new nut line

* mark each scale length down the apropriate string and join the dots on those too

you can just use the edge of the fretboard to lay out your scales rather than the string line, it works just as well...but obviously your low string would be just slightly less than the stated scale length and your high string just slightly more, not an issue as long as you remember that when placing the bridge

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You can also use this handy-dandy online calculator: http://www.fretfind.ekips.org/2d/nonparallel.php

Just stick in your two scale lengths, string width at the nut (not the nut width), string width at the bridge, fretboard overhang, "0.33258" for the perpendicular fret distance (for the 7th fret), # of frets and # of strings. Leave the rest of the fields as the default, and it'll spit out a spreadsheet of distances and angles. In that spreadsheet there'll be an "angle" column and a "mid to nut" column which can be used to measure the distance from the nut at the centerline and the angle of that particular fret (assuming you have a digital protractor). Mark it, slot it, fret it and you're done. Easy breezy.

Edited by DC Ross
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Thanks guys...sorry for the delay...I kinda forgot that I even posted this. :D

Ok....so I used DC Ross's calculator and it spit out a convenient DXF file. This should be good.

I have a question about the neck. Do you use a normal scarfed headstock? If so is there just some extra "flat" or fretboard surface above the angled nut where the nut angles away? Does that question even make sense? I guess what i'm asking is does the angle created by the scarfed headstock stay perpendicular to the center line of the neck.

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Thanks guys...sorry for the delay...I kinda forgot that I even posted this. :D

Ok....so I used DC Ross's calculator and it spit out a convenient DXF file. This should be good.

I have a question about the neck. Do you use a normal scarfed headstock? If so is there just some extra "flat" or fretboard surface above the angled nut where the nut angles away? Does that question even make sense? I guess what i'm asking is does the angle created by the scarfed headstock stay perpendicular to the center line of the neck.

You can do it any way you like. I prefer scarfing on all necks if angled headstocks are involved. If you want an angled nut but have a "straight" headstock then leave the end of the fretboard at 90° to the centreline but you'll have a triangle of fretboard material spare. You may have troubles with the higher strings fouling on the extra fretboard material if they break over the nut towards an angled headstock in that case.

If you have an angled end to the fretboard, then an angled headstock's "treble side" will sit lower than the bass side - the twist as Jammy mentions. I'm in the middle of building a compound scale instrument right now....the angle of the headstock scarf is 12°, although it is offset due to the nut's angle. The angle on both sides is still 12°. This will result in a twisted headstock, but straight string paths relative to the headstock.

bwsemi8_6.jpg

Edited by Prostheta
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so far i have done standard headstock angles, if you are not doing massive differences in the scale lengths then the little triangle of extra wood behing the nut isnt a problem. on my last one i just rounded it over subtley and its hardly even noticeable - certainly doesnt look bad. although on my first i was never quite happy with the behind the nut situation

obviously a more angled nut will increase the chance of the high strings hitting it

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Totally. I'm a rocket scientist, so having a twisted headstock and other eccentricities just serve to turn more heads. I'll be popping a headcap with recessed tuners into this one again :-D

Materials:

bwsemi8_7.jpg

(please - no off-topic discussion on this build unless it pertains to the original thread itself...i'll do a build thread soon)

Edited by Prostheta
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