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Does anyone know the math used to derive the locations? I’m working on a guitar right now that requires a larger pin spacing than the max provided by said ruler…

laying out a nut is simple
first start with the 2 E strings 1 and 6 I set them at about .100 from the edge of the fretboard.
then layout the remaining strings by measuring the width from the center of the slots and divide by 5
usually comes out at .295 to .305 I use a very sharp pencil and then notch them with the .013 nut file and remeasure
and adjust if needed

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Hi Ed,
For bridge pins I measure the width of the fingerboard at the 12th fret (mid point of the string length) and use that as the E to e spacing of the pins. I then divide up the distance into 5 equal parts (for a 6 string) and use that for the centerlines of the pins.
The width and - taper - of the fingerboard somewhat determines the spacing of the strings at the bridge (if you want the outer strings to follow the edges of the fingerboard). You can fine tune string placement a little bit by where you notch the pin holes (unslotted pins).
Others may have a better method or explanation, but that is how I do it.

The Stewmac ruler is not equidistant. The spacing increases from treble to bass to account for the thicker diameter of bass strings. I don't know the math but I would measure the % increase from one notch to the next in a few locations to see if a constant % factor emerges. If so you could extrapolate it out to your desired width.

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Stay with the happy people.
--Reynolds Large

I think Ed’s question relates to the proportional spacing on the StewMac ruler. The SM ruler leaves slightly smaller string spacing as you go from bass to treble.


Steve

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Steve Smith
"Music is what feelings sound like"

Ed, have you tried using the scale with double or triple spacing? Move the scale so that when the e's are on point, the rest of the points work with every other, or every third slot.

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Why be normal?

At the nut with the closer spacing the thickness of the string has a greater impact on the playability of the instrument, but even there not everyone accounts for it. At the bridge pins I think it is much less critical, and even there you can finesse the spacing by how you cut the string slots.

The math is this. Layout the two outer strings where you want them. Measure the total "air gap" distance from the inside of the two E strings. Add up the diameter of the other four strings and subtract that from the total air gap measurement. Divide that by five. That is the air gap between each string. Set your caliper to the air gap and start setting the strings down working from each side. You should meet in the middle with no error.

I use to do this for every guitar that came through my shop back in the good ol' days before the SM ruler.

Ditto. If you know how wide the nut is, and you know how far away from each side you want the outer strings to be, and you know the diameter of each string, you can just lay this all out on a simple diagram and compute the space between the strings. It’s not hard at all. The StewMac ruler just makes it even easier. I love the tool, but it is not essential to this task.

This is correct. The maths are a bit more complicated then simply dividing by 5 because they take into consideration the width of the strings and I would assume that width is an average of string gauges. Without the ruler though the divide by 5 rule works perfectly fine. I actually use the ruler to mark out pin spacing too... Why not?

The Stew Mac rule increases the air gap by 0.010" from treble to bass. So it is an approximation. Doing the math gets you with true equal gap settings. But the difference is so small it makes little difference.

For spacing at the saddle/bridge pin holes I use equidistant spacing, any difference due to string widths is not nearly as noticeable at the picking end .
Certainly no client has ever even noticed, and I can't tell any different when I play, I have tried it with the SM rule spacing.
I drill the pin holes using a Cross Slide Vise to 0.05 mm so I could do pretty much anything, just call me a slob.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I laid out the equivalent of SM's ruler with an array of lines whose distance apart increased by .010", then printed it. It looked sort of like this, exaggerated:

| | | | |

You can go as narrow or wide as you want.

I stopped doing it because nobody noticed but me.

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formerly known around here as burbank
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http://www.patfosterguitars.com

I use math as stated above. Most builder use center line but in reality it won't matter much. Since the string spacing at the bridge is on centers the nut should follow.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I notice the difference on narrow necks. The wound strings feel a bit crowded in the first position and I end up stopping strings that should be open.

For bridge pins, I use a proportional divider which I first saw on Frank Ford's site. Makes it very easy and quick to mark out pin placement.

Thanks for the very good answers!

For context, this is about a 26.5-25.5 multi scale with a 1 13/16 nut measured parallel, so the string spacing at the bridge is quite skewed. The most excellent SM ruler maxes out at just over 2 3/8, this project is 2 1/2 almost on the nose.

Time to go for a walk and do some thinking about why I agree to non standard projects, lol.

It seems like your project would be perfect for the math approach.

Ed, see Sections 4.8.14 and 21.5.3 of the Build book. I'm still using the one I made over 20 years ago and it has been used on everything from small steel strings, classicals to baritones and 12 strings. The slot increment is 0.1mm. It took me about an hour to make mine, but it pretty well lasts for ever. And all of my projects are non-standard, but I do refuse some of them!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks!

This place is great btw!

If you really are not happy using someone else's notion of ruler layout, some very simple graphical layout will give you the Stewmac rule proportional layout for the gap in that tool's capabilities (see below) or the in-betweens.

The layout shown is for increasing the spacing, but another projection onto the vertical axis will give reduced spacings.



There are gaps in the SM nut ruler layout... less than 0.65", between 1.2" and 1.35", and greater than 3.35". The graphical method above addresses all of these gaps.

Mr. Bond: The proportionality for double and triple (or even quadruple) spacing remains constant, so I am assuming your pin spacing is one that falls into a gap between double and triple spacing, or triple and quadruple spacing. If so, the graphical method above should serve very nicely. This same method may be used for equal spacing without resort to proportional dividers... simple lay out with a good rule at cardinal markings and project onto the diagonal at desired pin spacing.

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For the times they are a changin'

- Bob Dylan

Thank you!