Purchased fretboard doesn't match my Uke plans

javie123

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Greetings!

My first post in this forum. I've built a mandolin and a ukelele, the latter using these plans from Oaktown Strings, which I found to be quite satisfactory for my first build. On that, I cut my own fretboard and slots using the template in the plans and all seemed to work well. I am now building three ukes at the same time, and ordered two pre-slotted fret boards from Luthier's Mercantile (before they went out of business). I'm fairly well versed in construction methods, but somewhat unfamiliar with the math around fret spacing and the like. So, I'm confused about why the LMI pre-slotted board differs quite a bit from the fret slot spacing in the Oaktown plans; the LMI board slots are slightly closer together, but that results in a fairly large (e.g. 1/8" or more) difference at the bridge-end of the board. The LMI board has a sticker that indicates a scale length of 17"; so too the Oaktown plans.

So--wondering why the spacing is different? If I use the LMI boards, (how) should I adjust the plans?

Thanks for any help from anyone out there.

Jeff from NJ
 
Greetings Earthling!

This seems to be a question of: Will the true 17th inch scale fretboard please stand up.

The first thing to check is the measurement from the end of the fretboard (where the nut would be) to the 12th fret slot. It should be 8.5 inches or half of a 17 inch scale fretboard. If it isn't... well Houston we have a problem.

To see a fret calculator (the distance between frets) go here:

 
If I use the LMI boards, (how) should I adjust the plans?
I would want the neck to join the body at a fret location - usually 12th or 14th - so that's where I'd start. Pick the same join location as for the first uke.

Now comes the measuring! The length of neck from nut face to joining fret must match the fretboard. So if your LMI boards are shorter, the neck needs to be a little shorter; if longer, longer. In practice, that means starting your headstock taper at a different point. The neck width might be fractionally different from plans, but you'd make the neck a little over-width and then shape it back to the fretboard.

In theory you could adjust the body too, so that the bridge (more accurately, the saddle) sits at the same spot in relation to the body. In practice, 1/8 inch or so won't make any real difference except:
  • your bridge plate needs to move as well, and
  • if you are using a pin bridge, you need to check that the holes don't intersect any bracing. I'd just draw the bracing and new bridge and pin hole locations on the underside, to make sure.
 
Back in the recesses of my mind I think at one time LMI tenor uke fretboards may have been 17.1ish inches scale (Allen Guitars' boards that I use are 17.108"). I once deduced that this may have been based on a 650mm classic guitar scale with the first 7 frets removed, or something similar. Measure as carefully as possible from the nut location to the middle of the 12th fret and multiply by two - that is the scale length. I use the Stewmac fret position calculator to predict the saddle position (see sequoia, above). For the 17.108" scale, it is 437.1 mm (easier to measure in mm).

In any case, the adjustments I would make for a slightly 17+ scale would be to finesse the position of the "attachment point" fret toward the headstock slightly (width of a fret and a half or so) and call it a day. It is critical that the final bridge position corresponds to the corrected actual scale length. My bridge patch/plate is sufficiently large that a 1.5mm shift won't make any difference. Good luck.

(If the scale were slightly shorter than 17" I'd move the "attachment fret" position the other way slightly.)

YMMV - I believe at least one high-end builder represented here maintains a very tight tolerance between the position of the front of his bridge and bridge patch. I am a hobby builder using little fixturing and those tolerances are not possible even in my base case.
 
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OK. So during my lunch hour I did some measuring. What I found:

* The Oaktown plans are I believe inaccurate as far as the 17" scale length being correctly rendered on the drawing. The distance between the fingerboard side of the nut and the saddle is not accurate in that it's 16 7/8" from the that side of the nut, but exactly 17" from the STRING side of the nut. And when measuring from that point (the string side of the nut), it is indeed exactly 8.5" to the 12th fret, as it should be for a 17" scale length.

* The spacing for the Oaktown plans do not conform at all to the Stewmac fret calculator, as cited above. For example, the distance from the nut (in this case, the STRING side since that is 17" from the saddle) is 27mm vs. 24.25 according to the Stewmac fret calculator, quite a big difference. However, they are not that far off at the sound hole end of the fretboard, as it is 287mm at the 19th fret vs. 287.84 according to the calculator.

* All of the above is clearly illustrated in the attached photo.

* The fretboards purchased from LMI do indeed conform exactly to the Stewmac spacing as specified in their calculator.

So - shall I inform the Oaktown Strings site that their drawing is inaccurate? At least as far as the accuracy of the nut placement? And shall I use the LMI boards, and use this spacing for the fretboards that I'll be cutting by hand? Still a bit mystified as to why the spacing is rendered as it is on the Oaktown plans. I did build one uke with these plans and it sounded fine (I gave it to a friend so can't test it now...).

Any further advice much appreciated.
 

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In the above, by "string side," I mean "PEGBOARD" side of the nut....
 
Measure from the flat side of the nut where it butts up against the fretboard. The peghead side of the nut has nothing to do with anything... Yes, it looks like from what I can tell that the plans are incorrect. Just go with the LMI fretboard and ignore the plans. 14th fret to the body. Just make sure the saddle placement is correct: 17 inches plus 3/32" compensation.
 
From the photo of that fret board, it appears that the ruler is not measuring from the 0 fret.
I use the mm scale all the times as it is easier for me to read.
Measure from the 0 fret to the 12th and double that distance + 2 mm for the saddle placement when installing that fret board.
 
The problem here seems to be that there is indeed a zero fret slot. One either needs to use a zero fret (my recommendation) in which case, as spongeuke pointed out, you measure from the zero fret slot, NOT the end of the fretboard itself. If you want to use a standard nut you would cut the board off through the zero fret slot.
 
I have this plan so dug it out to take a look.
Measured from the string break point to the 12th fret, along the centre line, not the splayed path of the string path, it is slightly out but not that much.
IMG_6730.jpegIMG_6731.jpeg
 
Perhaps there are discrepancies between printers or software?
There shouldn’t be but it wouldn’t surprise me.
The measurement to concern yourself with is the actual scale length of the fretboard you plan to use.
The bridge plate and bridge need to be placed accordingly, or if you’ve already built the body exactly to the plans then you may need to join the neck to body at just slightly off the 14th fret position to ensure correct bridge placement.
 
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Perhaps there are discrepancies between printers or software?
There shouldn’t be but it wouldn’t surprise me.
The measurement to concern yourself with is the actual scale length of the fretboard you plan to use.
The bridge plate and bridge need to be placed accordingly, or if you’ve already built the body exactly to the plans then you may need to join the neck to body at just slightly off the 14th feet position to ensure correct bridge placement.
Yeah maybe it was not professionally produced but home printed with fit to page checked.
 
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