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I get a fair number of refrets and fret dresses in and have observed that the acoustic guitars with a higher string height above the soundboard, in general, seem to give more volume up to about the 1/2" normally quoted here in most discussions. (vs 14mm or 0.551" at the 1st string in the Gore and Gillet book)
Using the normal calculations, I've aimed for this 1/2" with my builds.
Yet I've ended up when measuring my final string height above the soundboard with a consistently lower figure, by around 1mm (0.040")
I had been thinking I must be getting more pull-up of the soundboard than others for some reason, and it's been annoying me.
This morning it dawned on me.
I measure string height at the outer strings, the same way I measure the action at the 1st and 6th strings.
And I have not been taking the fretboard/saddle radius into account, I was calculating for the highest point, around the middle of the saddle
For my 16" radius FB and a 56mm string spread at the saddle (my fingerpickers), the Sagitta or displacement of the arc of the fretboard and saddle is nearly 1.0mm, and it would be nearly 1.3mm for a 12" radius FB.
This is something I have never seen pointed out in neck geometry posts on the OLF when talking about aiming for a height of around 1/2", or even in Gore and Gillet, so thought it might be worth bringing up.

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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.

Good point Colin, I also measure my 1/2" at the center and never thought of the outside strings. Be interesting to see some of the comments from our fellow luthiers.

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Steve Smith
"Music is what feelings sound like"

I've always measured in the center too. But even so 1/2in plus or minus a mm here or there is no big deal imho. Having said that, I have learned that I need to give a lot more room for top deflection then books have suggested. I think in Cumpiano and Natelson the say go no more then 1/32 over the bridge or so. I typically double that.

Is this measurement made with the frets in?

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Hutch

Get the heck off the couch and go build a guitar!!!!

Doesn't matter. We're measuring height of strings above the soundboard.

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Steve Smith
"Music is what feelings sound like"

[quote="jfmckenna"...………. I have learned that I need to give a lot more room for top deflection then books have suggested. I think in Cumpiano and Natelson the say go no more then 1/32 over the bridge or so...…………..[/quote]
Unless the soundboard/bracing is much stiffer than needed, that's for sure.

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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.

We measure using the underside of the D string (usually the highest string), and always include body distortion as opposite sign of the other numbers. Dread, GA, SJ, and other larger guitars see 1/16" of 'top rise' (really, body distortion) which serves to drop string height over the top once action is readjusted, while a 000 or OM may see 0.045", and an O and smaller between 0.030" (O) and 0.017" (Size 5). Obviously, these numbers are for planning - top thickness, bracing, and body construction will determine just how much the body changes shape (and how long that takes) under string tension.

A decent visualization tool:

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For the times they are a changin'

- Bob Dylan

On page 4-34 of Design I say "...when the height of the tuned strings above the soundboard is 14mm (steel string guitar) when measured at the 3rd and 4th strings". I can't recall ever saying measure the the string height above the soundboard at the first string.

Regarding the sagitta of the saddle, in Section 21.6.1 I talk about saddle curvature, usually making the saddle slightly more curved (smaller radius) than the fretboard, because the 3rd and 4th strings are usually the ones more prone to rattling.

So it's all there. It is not necessary to talk explicitly about different fretboard radii in the neck angle discussion because it is intrinsically embedded in the calculation.

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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

Didn't refer to at 4-34, section which appears to be on bridge rotation basically.
Should have worn my prescription glasses when reading pg. 4-91, (effect of fretboard relief) which says "14mm at the 4th", not the 1st, (1st edition) humble pie for breakfast today...
Section 21.6.1, I see nothing about saddle curvature, re-read it several times, I must be going completely senile!
Anyway, I have developed my own technique to combat rattles, typically delivering actions of 2.0mm bass/1.0mm treble, or lower, with light/custom light strings, for players wanting low actions, or of course older players with advancing hand and wrist problems.

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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.

No, you're not Colin! I was quoting from Edition 2. Apologies. I re-wrote the second half of the 2nd paragraph in 21.6.1!

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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

Phew! A temporary reprieve at least.
Got round to a list of any changes/additons by any chance?

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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 generally shoot for a string height above the soundboard of 7/16ths. Although the greater 1/2 inch distance above the soundboard makes for a louder guitar it also seems to make the sound a bit more strident on my instruments.

Yes of course, I know of several makers who vary string height to suit the guitar/intended style of playing.
I was referring to the generally accepted 1/2" as the oft quoted maximum beyond which I believe there is a possibility of over torqueing the bridge / choking the response.

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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.

No, I'm afraid not, Colin. Whilst the book is probably at least 98% the same, there are bits and pieces like this example that I've changed and I have no idea where they all are now! Most of the changes were just typos and re-phrasing/clarifying bits where it was possible to misconstrue things. I changed a few pictures, added a few, recolour-balanced them all, added a bit more to the Intonation section to prove the inherent sources of intonation errors, and a few other bits and pieces that I can't immediately recall. All the section numbering and the pagination remained essentially the same.

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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

Top rise is going to vary with every guitar. While you may target a specific height, this is not an act of high precision (i.e. variations in the tens of thousandths). Honestly if one can consistently control geometry to achieve 0.040" precision, you're in a small group of people that do so. Martin just throws on different thickness bridges to compensate for lack of control. Some classical guitar makers are known to plane fretboards to get to a target height. It sounds like you're doing fairly well!

Along these lines, I've wondered what people use as the typical thickness for their bridges (mine are apprx 3/8"). I aim for 1/2" string height above the soundboard.

Frankly I'd be embarrassed if the way I achieved a proper neck angle and string height at the bridge above the top was to simply swap out different bridges. There are better ways to do it. One of which was mentioned above in the classical tradition, plane the fretboard. The other is to just figure out how to plane the rims ahead of the soundhole to produce an angle that gets you within acceptable limits. Lots of ways to skin that cat, I suppose swapping bridges is one of them, but I never liked that. The target height of the strings over the top at the bridge should be set for what ever tonal profile the luthier is going for. Having to fudge that after the fact changes that profile.

It's easier to swap bridges. And if you aren't concerned about the tonal profile there is a wider range of string heights above the soundboard that is "acceptable" (3/8ths to 9/16ths). Seems like someone at Martin once said there is always someone who will like the sound and buy the guitar.

this is an interesting discussion. I can tell you that it took me a while to dial in what I needed.
When setting the neck I am looking for 3/8 off the top at the point of the saddle with the frets off.
with the frets I will be about .037 higher.
It is hard to know exactly how much the top will deflect and we know that it will. So when I set up a guitar I start with a .375 thick bridge. After the neck is set I can now dial in the bridge . In a perfect set up for me I am looking for about 3/32 off the top of the bridge. I usually end up with a .350 bridge and .150 to .180 saddle when done.
I don't like to go much lower. Also don't get too into setting the final saddle until your guitar settles in. I will string them up and let them set a few days to make my final adjustments. On that same point I like to adjust intonation after at least a week or 2 as the top will rise and your bridge will torque a bit so let the box become a guitar before you make that final set up. Patience is the hardest thing to learn

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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