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Nut position.
https://luthiersforum.com/forum/viewtopic.php?f=10101&t=55472		 Page 2 of 2
Author:  Ken Lewis [ Thu Jan 26, 2023 6:09 pm ]
Post subject:  Re: Nut position.
guitarjtb wrote:
doncaparker wrote:
I don't worry about it. I glue the bridge on without a saddle slot, string it up, then determine where the saddle has to sit for intonation to be just right (using temporary mini-saddles for each string), mark the locations, then rout the slot. This way, I don't have to sweat bridge location too much during gluing; ballpark is OK. It requires having enough open space on the bridge to cut the slot where it needs to be, a little this way or that way.


Right. I slot my bridges after they are glued on. And I can get the saddle in the correct location, with temporary saddles. My question was on the theory of the measurement, from the 12th to the saddle, with a compensated nut.


Consider this. If you move the nut back by the half kerf distance and do nothing else, when you fret a string the nut is removed from having effect on any other note. So.... the saddle has to move so that a perfect octave of the open string note happens at the 12th.
Author:  doncaparker [ Thu Jan 26, 2023 6:33 pm ]
Post subject:  Re: Nut position.
Maybe I should clarify what I said earlier. I don't worry about it because, first, I only use a half kerf of compensation (which is about 0.012", which is not enough to throw any rough measurements off), and second, I'm using real world intonation comparisons on the guitar, instead of trying to plot out the right saddle placement for a pre-slotted bridge. I just place the bridge using a normal "scale plus compensation" rough idea of where the saddle should go, then worry about actual saddle placement after the bridge is glued on. Since the compensation is only a half kerf (again, around 0.012"), nothing about it will throw my saddle placement off by very much. I find that there is plenty of room for adjusting where the saddle will go. I try to avoid the temptation to spend time on gaming out in my head what happens on a theoretical basis. Math make Mongo head hurt.
Author:  Ken Lewis [ Thu Jan 26, 2023 7:12 pm ]
Post subject:  Re: Nut position.
I hear you Don. just trying to clarify for guitarjtb as they were asking about what happens with the saddle position.
Author:  bcombs510 [ Thu Jan 26, 2023 7:28 pm ]
Post subject:  Re: Nut position.
To make sure I fully understand:

- Is this shortening of the distance from nut to 1st fret by 0.012” a by product of builders using fret slotting templates? The way I’m understanding it is that with a template you can cut the 0 fret but what most do is keep going, cutting through the board. Theoretically the saw is cutting exactly centered on 0, that takes half a kerf (0.012”) of the presumed 0.024” saw off the end of the board. Correct?

Before people used slotting templates was this not a consideration?

- What is happening in factory settings? Does this also occur? Generally speaking of course. I suppose not because of the tuning trick described above.

Fascinating stuff. Thanks for letting me learn. :)


Sent from my iPhone using Tapatalk Pro
Author:  doncaparker [ Thu Jan 26, 2023 7:36 pm ]
Post subject:  Re: Nut position.
bcombs510 wrote:
To make sure I fully understand:

- Is this shortening of the distance from nut to 1st fret by 0.012” a by product of builders using fret slotting templates? The way I’m understanding it is that with a template you can cut the 0 fret but what most do is keep going, cutting through the board. Theoretically the saw is cutting exactly centered on 0, that takes half a kerf (0.012”) of the presumed 0.024” saw off the end of the board. Correct?


Brad--

Yes as to all of this. I am not qualified to talk about the rest of your questions. Mongo only helpless pawn in game of life. :D
Author:  guitarjtb [ Thu Jan 26, 2023 7:41 pm ]
Post subject:  Re: Nut position.
James not want to make Mongo head hurt!
Author:  Ken Lewis [ Thu Jan 26, 2023 7:56 pm ]
Post subject:  Re: Nut position.
Brad, I remember reading somewhere that some factories do the fretboard shortening thing. It's considered a quick and dirty nut
compensation. Good information on it and full nut compensation in Trevor Gore's books.
Author:  J De Rocher [ Thu Jan 26, 2023 8:27 pm ]
Post subject:  Re: Nut position.
bcombs510 wrote:
To make sure I fully understand:

- Is this shortening of the distance from nut to 1st fret by 0.012” a by product of builders using fret slotting templates? The way I’m understanding it is that with a template you can cut the 0 fret but what most do is keep going, cutting through the board. Theoretically the saw is cutting exactly centered on 0, that takes half a kerf (0.012”) of the presumed 0.024” saw off the end of the board. Correct?

Before people used slotting templates was this not a consideration?

- What is happening in factory settings? Does this also occur? Generally speaking of course. I suppose not because of the tuning trick described above.

Fascinating stuff. Thanks for letting me learn. :)


Sent from my iPhone using Tapatalk Pro



I don't know the history of this practice, but if you order a custom slotted fretboard from LMI, they give you two options for the position of the slot that determines the end of the fretboard. What they call the "Standard nut slot" offsets the saw blade toward the headstock so that the edge of the slot gives no compensation. The "Zero Fret" option centers the kerf so that if you don't actually use a zero fret and use the edge of the slot as the nut position, the end of the fretboard is shorter by 0.012" and introduces some compensation.

Attachment:
standard-nut-slot-position vs zero fret position LMI 2.jpg
Author:  DennisK [ Thu Jan 26, 2023 8:57 pm ]
Post subject:  Re: Nut position.
guitarjtb wrote:
Dennis:
"The bridge has to be placed closer to the 12th fret than usual."

This was also my assumption.

Clay:
"The original scale length should be used to figure the compensation at the saddle"

This would indicate that the bridge and saddle location are not affected by the nut compensation.

Could someone flip the light on for me?

The bridge is still farther from the 12th fret than the theoretical scale length. Just not as far as usual. Next time you're positioning a temporary saddle, try ignoring the open note and adjusting until the fretted notes are all as close to perfect as possible. You should end up with around half as much compensation as usual, and the open note will be very flat. If you can also move the nut, then you can fix the open note without affecting the fretted notes. But if all you can move is the saddle, then the only choice is to keep going farther because it flattens the fretted notes more than it does the open note. Eventually you will arrive at the usual position where the 12th fretted note is exactly 2x the open note, but lower notes are a few cents sharp and higher notes are a few cents flat.

Oh, and incase it wasn't clear, 3/32" is not a uniform nut compensation. Only a uniform shortening of the board. The string breakpoints are adjusted individually. Some are less than 1mm from the theoretical zero fret location.
Author:  Clay S. [ Fri Jan 27, 2023 12:22 am ]
Post subject:  Re: Nut position.
As Dennis mentioned, the idea behind compensation is to "flatten" the fretted notes to compensate for the increased tension (from pulling the string down to the fingerboard) and string stiffness (because a shorter string is stiffer than a longer string all other things being equal), both of which tend to "sharpen" the notes as you go up the fingerboard. Most of it can be done at the saddle, but when you shorten the distance from the nut to the first fret you are decreasing the string length slightly, so when you tune the string to standard pitch you are reducing the tension that was needed to bring it to that same pitch when the string was longer. The frets being in the same position they were at before nut compensation was added and the string tension being decreased, will theoretically play flat - but the string stiffness and tension increase from fretting will "sharpen" them back in tune. Hopefully...
(The clarity of my explanations is where I earn my name) Arthur Benade in "The Fundamentals of Musical Acoustics " ($8 used Amazon) explains things so much better.
Author:  Colin North [ Fri Jan 27, 2023 4:53 am ]
Post subject:  Re: Nut position.
DennisK wrote:
guitarjtb wrote:
Dennis:
"The bridge has to be placed closer to the 12th fret than usual."

This was also my assumption.
......................
Oh, and incase it wasn't clear, 3/32" is not a uniform nut compensation. Only a uniform shortening of the board. The string breakpoints are adjusted individually. Some are less than 1mm from the theoretical zero fret location.


That explains the 3/32", very similar to Trevor Gore in the book, shortening the FB at the nut end then compensating the break points for individual strings.
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