Help needed for measurements on fanned fretboards...

Discussion in 'Luthier's Corner' started by Pesh, Dec 6, 2017.

  1. Pesh

    Pesh Senior Member

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    Hi all,

    I read earlier today a thread regarding a fanned fret Firebird build that one of our resident builders is currently undertaking.

    It got me thinking, as fanned frets is something I'd be looking at doing on a build in the future, about how measurements are made for these.

    With straight / regular frets, the centre-point is X-distance from the nut, and seeing as the fret is parallel to the length of the nut. If you have a measurement start point at the nut (call it point 'a') and a second point which will be the centre of the placed fret (call it point 'b'), this will be constant wherever you measure on the length of the fret and comparative point on the nut.

    However I noticed that with fan frets, there is potentially 3 measurements one could make to accurately place a fret, and given that almost all frets are at an angle to the nut rather than parallel, the bass end of a frets' a to b measurement will be different to the treble end of the frets' a-b measurement. Which is fine.

    The problem is, I don't know at what point you would measure the fret placement points.

    I've got a picture attached with the three measurement points I've considered. I'm using an example of a 25.5" scale on the bass side, and a 24.75" scale on the right-side. I've got a collection of the various measurements of fret placement from the StewMac fret position calculator.
    • The top drawing is where the a-b measurement is made along the lengths of a fretboard blank. If using this method, the various points for the 25.5" scale are plotted along one edge of the fretboard blank, and then the various points for the 24.75" scale are plotted against the other edge. The points are joined up so you get line placements for where the frets would be, but the exact start and end points aren't ever on the actual fretboard after shaping it (the pink line overlap).
    • The middle drawing is where the a-b measurements are made along the edge of a shaped fretboard (i.e. where you have set the fretboard width at the nut and 12th fret). Like the first drawing, the measurements are made along the edges to the nut position. However this, as far as I understand it, would result in different placements from the top drawing method, as the width of the piece of wood means you'll have a slightly different start and end point using this edge.
    • The bottom drawing is similar to the middle, but measures the scale from the nut to a point directly under the outermost strings. This would mean that the scale length measurements would be exact at the point where you fret a string. It's hard to tell this in the picture of the drawing, sorry - I used small paper, thick-nib pens. I couldn't have drawn this as quickly in something digital at the moment.
    [​IMG]

    Could anyone advise which of these methods to use, if indeed I should use any of them at all? perhaps I'm over-complicating things, perhaps there is a better method?

    I'm looking for some info from those of you in the know, those of you who have made such things happen in the past and how you did it.

    Thanks in advance!
     
  2. Ripthorn

    Ripthorn Senior Member

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    If I were you, I would go to the fretfind2d page, which will do all the math for you and you can export it in a number of files. It's how I do it, and I've done it for several builds.
     
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  3. ARandall

    ARandall Senior Member

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    You have to find the path that the string takes....after all thats the bit that is playing the note and has to play in tune all the way along.
     
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  4. KnightroExpress

    KnightroExpress Senior Member

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    +1 for Fretfind, it's a great tool for planning out multiscale fretboards.
     
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  5. WhiteEpiLP

    WhiteEpiLP Senior Member

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    The problem with your idea is fanned fret guitars also have an angled nut. So 25.5 and 24.75 is a 3/4" difference, not much but a difference of 3/8th off 90° at both ends. So if the center point is the 12th fret it would be the straight fret and then you could just use the knowen measurements of the fret spacings for thise 2 scale lenghts marked fromthe center out both ways.
    Ultimately as lkng as you place the individual bridge saddles in the right place it should work.
    Of course this is all me thinking it out in my head having never done this and 5 beers in so what do i know. I could be way off.
     
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  6. charisjapan

    charisjapan Silver Supporter

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    Hey @Pesh !

    Really, there is only one way to make a fanned fret guitar work, and that is using the two outboard strings. Anything else would sound really weird.

    My Limba 6 Multiscale is 628mm~648mm ... very nearly a Strat bass E and a Gibson treble e ... so about what you were using as your example. Mechanically, all you have to do is set those two lengths, then decide where you want the single perpendicular fret, then all the other things will be decided from there. That's what FretFind2 does, but also tells you the fretboard dimensions after you decide how much overhang you want on each side. I set my perpendicular at the 7th fret, as I like to noodle around in Bm. You can set it anywhere that you are comfortable with, also keeping in mind how much angle you will have at the nut and bridge for design and esthetic purposes. Remember also that you will need a bridge that accommodates what you want (Hipshot makes 11 degree and 18 degree), or use individual bridges (Hipshot makes those, too).

    Just go to http://www.ekips.org/tools/guitar/fretfind2d/ , decide your perimeters and print it out! Tape the 3 pages together, snip it out and you will have an exact representation of your fretboard, and can even check all the measurements with their very comprehensive list of every single fret/string intersection. With this you can visualize your future guitar! :)

    :cheers2:
     
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  7. Pesh

    Pesh Senior Member

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    Thanks very much for the feedback on this. It was your limba thread that had me thinking about the problem and how to solve.

    I had designed a solution where the two scales, and therefore fret positions were measured using the outside edges of the shaped fretboard (example 2 from my crude drawings) but I can see how this would be flawed. Depending on the overhang of the fretboard the scales under the string would be shorter than what one might want, and it could also adversely affect bridge placement.

    I'm creating a new solution based on the fret finding tool for this one. I'm quite into designing things in CAD / CAM so I'm doing this in Fusion 360, so I can export carving / cutting into a CNC, or export the pattern into a laser cutter which I can use to trace lines with hand tools later.

    Thanks again!
     

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