"space behind nut" in a CNC'ed fretboard?

TheDudeAbides

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When I was shopping for fretboard material I noticed there was only an $8 difference between a blank board and a CNC slotted board, so I bought the CNC'ed option with a 17" scale length for the tenor I am building.

I am however confused about what the "space behind nut" measurement is all about?

There's about 3/8" of space behind the top slot that will need to be removed, not 1/8"(0.125") so I'm confused about that measurement. I presume it's important since it was on the label, but I have no idea what it's for?

If I measure from the nut(very 1st slot on the board) to the 12th fret it's at 215.5mm. Shouldn't the 12th fret on a 17"(243mm) fretboard be right at 217mm from the nut?

Either I'm doing something wrong here or LMII sent me a bad board. I presume the issue is me and am hoping someone here can educate me.

PXL_20220910_210844000~2_copy_1041x887.jpg

Tape and numbers to make sure I'm measuring the right slot 🙂

PXL_20220910_220851691_copy_1513x631.jpg
 
It looks to me like the top slot is for a zero fret.
 
That gives you two options. One is to cut the FB at the slot so your nut can butt up to the End of FB. Version two would be, route a slot for a nut kind of like a Fender detail.
That makes sense, and I had intended to just cut it at the 1st slot, however that puts my 12th fret at 215.5mm. shouldn't the 12th fret be at 217mm on a fretboard slotted for a 17"/434mm scale length?
 
It looks to me like the top slot is for a zero fret.
In theory I could install a zero fret there and cut it back a bit further. But that still leaves the question of the 0.125 soace behind the nut measurement.

I figured out the scale length, my book listed a 17" scale at 434mm but LMII cut it at 431.8mm and then listed it as 17"
 
In theory I could install a zero fret there and cut it back a bit further. But that still leaves the question of the 0.125 soace behind the nut measurement.

I figured out the scale length, my book listed a 17" scale at 434mm but LMII cut it at 431.8mm and then listed it as 17"
17×2.54=43.18 math agrees with LMII
 
17×2.54=43.18 math agrees with LMII
I concur.

Just irritated that I have 2 separate books on building Ukes, one says 434 and the other rounds up to 432, but then proceed to list tables for fret spacing with very specific decimal measurements. Very odd that they'd round up the scale length and then do the fret math based on that, though I suppose as long as 12th fret is the same distance to the nut and saddle it doesn't really matter.
 
I would just like to mention that in my experience the folks at LMI are really nice and helpful people, they also answer email questions quickly.
Yeah, I was planning to email them too, though not expecting a reply over the weekend so I figured I'd ask here too
 
i wouldn’t ‘fret’ too much about the exact mm length at this point. you’ll measure everything on the actual ‘uke before putting the bridge on. so if the scale length is listed an mm high or lower or if one plan says something or another, it’ll work out.

i am interested about the space behind the nut. i just assume for zero fretting but that’s just an assumption. or they need a little bit of wiggle room to get the cnc all lined up?
 
I concur.

Just irritated that I have 2 separate books on building Ukes, one says 434 and the other rounds up to 432, but then proceed to list tables for fret spacing with very specific decimal measurements. Very odd that they'd round up the scale length and then do the fret math based on that, though I suppose as long as 12th fret is the same distance to the nut and saddle it doesn't really matter.

there was a recent thread (and probably many more) talking about the distance from the 0-12 and 12-saddle. i think many folks were saying add 2mm to the 12-saddle to adjust for saddle height / compensation. that’s about what i do.

also then you can get extra detailed and adjust the saddle break for each individual string intonation. fun!
 
i wouldn’t ‘fret’ too much about the exact mm length at this point. you’ll measure everything on the actual ‘uke before putting the bridge on. so if the scale length is listed an mm high or lower or if one plan says something or another, it’ll work out.

i am interested about the space behind the nut. i just assume for zero fretting but that’s just an assumption. or they need a little bit of wiggle room to get the cnc all lined up?
I double checked the website and that slot isn't centered, it's offset so the edge of cut is dead 0 for the nut, which means it won't work for a 0 fret. I still have no idea what the 0.125 measurement is for, but measuring from the edge of that slot to 12 lines up, which confirms I just need to trim off everything above that edge.

I was only concerned with length now because the slots were precut for a specific scale length and I needed to make sure I cut the top edge off in the right place. I had originally assumed that edge was where the nut went but that "space behind nut" measurement had me 2nd guessing myself.
 
The difference is quoted scale lengths is nominal vs actual.
The nominal scale length is the distance from inside the nut (or the centreline of a zero fret), to the centreline of the 12th fret, x 2.
The actual scale length is the nominal scale length + saddle compensation.
Most discussions of scale length are talking about nominal scale length.
So, 17" or 431.8mm is the nominal scale length and 434 is the recommended actual scale length when saddle compensation is taken into account.

My two bobs worth, yes the board is manufactured that way to use with a zero fret or a nut. Actually it's a zero fret board which you chop down the centreline of the zero fret slot to make it a board for a nut. if your doing the measurements carefully you will say that the board is now a fraction short, yes it is, yet this is useful "Nut Compensation" which stops the intonation going sharp over the first few frets.

EDIT" If the distance from the zero slot to the end of the board is 3//8" rather than 0.125", then I have no idea what that measurement is either.
 
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I double checked the website and that slot isn't centered, it's offset so the edge of cut is dead 0 for the nut, which means it won't work for a 0 fret. I still have no idea what the 0.125 measurement is for, but measuring from the edge of that slot to 12 lines up, which confirms I just need to trim off everything above that edge.

I was only concerned with length now because the slots were precut for a specific scale length and I needed to make sure I cut the top edge off in the right place. I had originally assumed that edge was where the nut went but that "space behind nut" measurement had me 2nd guessing myself.
Some time back I checked with LMI and the dude is correct, the nut slot is offset slightly so it can NOT be used for a zero fret. The edge of the slot is designed to be the nut edge (start of string) rather than the center of the slot as would be required for a zero fret. This was about the time that I set up to slot my own boards as I always use a zero fret.
 
The difference is quoted scale lengths is nominal vs actual.
The nominal scale length is the distance from inside the nut (or the centreline of a zero fret), to the centreline of the 12th fret, x 2.
The actual scale length is the nominal scale length + saddle compensation.
Most discussions of scale length are talking about nominal scale length.
So, 17" or 431.8mm is the nominal scale length and 434 is the recommended actual scale length when saddle compensation is taken into account.

My two bobs worth, yes the board is manufactured that way to use with a zero fret or a nut. Actually it's a zero fret board which you chop down the centreline of the zero fret slot to make it a board for a nut. if your doing the measurements carefully you will say that the board is now a fraction short, yes it is, yet this is useful "Nut Compensation" which stops the intonation going sharp over the first few frets.

EDIT" If the distance from the zero slot to the end of the board is 3//8" rather than 0.125", then I have no idea what that measurement is either.
Yeah, it was about 3/8" of material behind the nut slot.

I also just realized when I started I must have assumed this book was for a 17" tenor so that's what I ordered, which is where some of my confusion was coming from too

According to the fret spacing chart the nominal would be 434mm based on the fret spacing measurements. I'm assuming that chart is for a custom scale length that's a bit longer. But at this point it doesn't matter, I'll position the bridge for the scale length I bought(compensated for actual scale length) and I'll be good.

PXL_20220911_150844202_copy_488x1210.jpg
 
There are too many numbers and too many references flying around, and the confusion is deepening.

I believe that the 434mm number is a red herring. Let that one go.
Let the chart you just posted go too. Right now its a big red herring.
17" is a traditional, NOMINAL scale length, and this converts to 431.8mm metric.
This is normal. This is to be expected.

Nominal scale length is the distance from inside the nut to the centreline of the 12th fret x 2.
Actual scale length is nominal scale length + saddle compensation.
So,
The zero fret to 12th fret distance that YOU have quoted is 215.5mm, when in theory it should be 215.9mm for a 17" (431.8mm) scale length. 0.4mm SHORT discrepancy.
At this point double measure for errors, and, a 434mm nominal scale length is right out. A bigger error in the wrong direction.

Try measuring centreline to centreline zero fret to 12th fret and see what the answer is?
Try measuring inside slot surface zero fret to centreline 12th fret and see what the answer is?

If the angle here you're checking is that the nominal 17 (431.8mm) scale is incorrect, then the correct length is slightly shorter.
However at this point we are definitely within the scope of measurement errors.
 
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There are too many numbers and too many references flying around, and the confusion is deepening.

I believe that the 434mm number is a red herring. Let that one go.
Let the chart you just posted go too. Right now its a big red herring.
17" is a traditional, NOMINAL scale length, and this converts to 431.8mm metric.
This is normal. This is to be expected.

Nominal scale length is the distance from inside the nut to the centreline of the 12th fret x 2.
Actual scale length is nominal scale length + saddle compensation.
So,
The zero fret to 12th fret distance that YOU have quoted is 215.5mm, when in theory it should be 215.9mm. 0.4mm SHORT discrepancy.
At this point double measure for errors, and, a 434mm nominal scale length is right out. A bigger error in the wrong direction.

Try measuring centreline to centreline zero fret to 12th fret and see what the answer is?
Try measuring inside slot surface zero fret to centreline 12th fret and see what the answer is?

If the angle here you're checking is that the nominal 17 (431.8mm) scale is incorrect, then the correct length is slightly shorter.
However at this point we are definitely within the scope of measurement errors.
Sorry, was just trying to explain where my confusion came from.

The 215.5 was me measuring with a standard steel rule, so it's entirely possible the rule wasn't right on the edge of the nut slot and threw my measurement off by 0.4mm, however at the time there was a far greater discrepancy than a fraction of a mm and my book, which is what stared this whole thread. I will double check again when I'm home but I'm guessing LMII is likely spot on at 215.9 on the board and I'll go from there.
 
Be sure and allow for proper placement of your bridge patch if utilizing one.
Should be, but the ukes closed up now so there's no moving it. Patch was placed to fit the saddle 17" from the nut, and since I'm new to this I added a couple mm of extra patch material which will hopefully compensate for the change in saddle placement as a result.
 
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