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  #31  
Old 01-23-2021, 08:05 PM
JohnFrink1 JohnFrink1 is offline
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Originally Posted by M Hayden View Post
The key point is not an arbitrary 1/2-above-the-soundboard for neck set.
Not to confuse things further, but back when I cared about the height of the strings above the top I kept measurements of some of the guitars I've owned.

RainSong GS-FLE - 13/32
Collings OM1T - 13/32
SCGC OM - 13/32
SCGC OM - 13/32
Martin OM18 GE - 14/32
Collings OM1T - 14/32
Collings OM1Mh - 14/32
Collings OM1MhVN - 14/32
Collings OM2HT - 14/32
Collings OM2HT - 14/32
SCGC DBB - 14/32
RainSong CH-OM1000N2 - 14/32
Brunner B-Compact - 29/64
Breedlove Northwest - 15/32
Collings OM1MhVN - 15/32
Martin OM15 CS - 15/32

These were all very nice guitars, by the way. No complaints at all.
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Collings OM1T, OM1Mh
Goodall TROM
Martin CS-OM15
RainSong CH-OM-N2
Santa Cruz OM

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  #32  
Old 01-24-2021, 03:31 AM
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Victory Pete Victory Pete is offline
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Quote:
Originally Posted by JohnFrink1 View Post
Not to confuse things further, but back when I cared about the height of the strings above the top I kept measurements of some of the guitars I've owned.

RainSong GS-FLE - 13/32
Collings OM1T - 13/32
SCGC OM - 13/32
SCGC OM - 13/32
Martin OM18 GE - 14/32
Collings OM1T - 14/32
Collings OM1Mh - 14/32
Collings OM1MhVN - 14/32
Collings OM2HT - 14/32
Collings OM2HT - 14/32
SCGC DBB - 14/32
RainSong CH-OM1000N2 - 14/32
Brunner B-Compact - 29/64
Breedlove Northwest - 15/32
Collings OM1MhVN - 15/32
Martin OM15 CS - 15/32

These were all very nice guitars, by the way. No complaints at all.
My Herd just got thinned out this past year but all of them had the 1/2" measurement.
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  #33  
Old 01-24-2021, 03:35 AM
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Victory Pete Victory Pete is offline
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Originally Posted by Victory Pete View Post
Both of these guitars have been lacquered and have gotten new strings. There is quite a bit of difference between them. They both had .050" clearance above bridge but have very different string clearances now. One is perfect and the other is pretty high. When I did these neck sets I did notice one was not at as much of an angle as the other. It was the one with the top that had no radius in it. I don't know why that had happened, both tops got glued the same way. I remember at the time that the tops, before braces, would sometimes warp if I left them on the bench overnight, I would then flip them over and they would straighten. I now hang them so they get equal air flow on each side. I guess if the top has no radius it will pull up more with string tension and that is how I got the high action. I did have the magic 1/2" string clearance to the top so I got some wiggle room to lower the saddle.
One thing I have noticed, the guitar with the flat top is very open, responsive and bassy, it would be great for finger picking. I think this indicates that the top is loose, I suppose from not have any stress in a radiused top. The other guitar with a small amount of dome to it's top, is very punchy and tight, that is how I like them being a strummer.
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  #34  
Old 01-25-2021, 09:20 AM
redir redir is offline
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Originally Posted by ArchtopLover View Post
Excellent post, this is exactly how I understand neck angle geometry for a flattop.

However, for archtops (which I prefer), neck-set geometry is not as critical a concern for the structural integrity of the instrument. Although, where tone and volume is concerned, the neck-set geometries importance comes into play when the builder is determining the string break angle at the bridge. This break angle parameter has enormous ramifications in the overall tone and volume of the instrument, and the builder can actually "voice" the guitar by simply raising or lowering the string break angle for a particular sound to be achieved. Of note, James L. D'Acquisto made his ebony tailpieces adjustable, so that the customer could play his instrument and have the tailpiece adjusted for optimal tonal preference. What is most interesting, in this regard, is that the tonal differences are well understood; a low break angle gives a warmer more plush tone with less volume, conversely a higher break angle increases volume, and brightens the overall tonal character, but adds some harshness and acoustic artifacts, that many archtop players find annoying or disagreeable, so, finding that perfect Goldilocks sweet spot is really tricky .
I don't have any experience with archies yet but the same could be said for flat top instruments too. In fact part of the reason I went to a bolt on neck is so that I could make very fine adjustments to the neck angle not for action and playability but for tone. It doesn't have so much to do with the break angle though. And if Alan Carruth comes in he can explain some of the research he did that shows that string break angle is not very important if at all on a flat top guitar in terms of tone, but what is, is bridge rotation. So if the bridge is rotated too far forward it can choke the tone. By lowering the neck angle the bridge rotates less and the guitar tone opens up. From many different experiments and measurements that rotation is accepted to be about 2deg.

So that's why this 1/2in string height at the bridge is not really a golden rule but an average. If a guitar I just built had a perfect 1/2in at the bridge but with 2.5deg rotation then I would adjust the neck angle to get back to 2deg rotation which would lower the string height at the bridge a bit. But I would rather have proper rotation which is actually meaningful then the 1/2in height which is not.
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  #35  
Old 01-25-2021, 09:40 AM
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Victory Pete Victory Pete is offline
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Quote:
Originally Posted by redir View Post
I don't have any experience with archies yet but the same could be said for flat top instruments too. In fact part of the reason I went to a bolt on neck is so that I could make very fine adjustments to the neck angle not for action and playability but for tone. It doesn't have so much to do with the break angle though. And if Alan Carruth comes in he can explain some of the research he did that shows that string break angle is not very important if at all on a flat top guitar in terms of tone, but what is, is bridge rotation. So if the bridge is rotated too far forward it can choke the tone. By lowering the neck angle the bridge rotates less and the guitar tone opens up. From many different experiments and measurements that rotation is accepted to be about 2deg.

So that's why this 1/2in string height at the bridge is not really a golden rule but an average. If a guitar I just built had a perfect 1/2in at the bridge but with 2.5deg rotation then I would adjust the neck angle to get back to 2deg rotation which would lower the string height at the bridge a bit. But I would rather have proper rotation which is actually meaningful then the 1/2in height which is not.
I am interested in this rotation factor. I did an experiment on break angle: https://www.acousticguitarforum.com/...d.php?t=448701
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  #36  
Old 01-25-2021, 11:01 AM
John Arnold John Arnold is offline
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Quote:
I don't have any experience with archies yet but the same could be said for flat top instruments too. In fact part of the reason I went to a bolt on neck is so that I could make very fine adjustments to the neck angle not for action and playability but for tone. It doesn't have so much to do with the break angle though. And if Alan Carruth comes in he can explain some of the research he did that shows that string break angle is not very important if at all on a flat top guitar in terms of tone, but what is, is bridge rotation. So if the bridge is rotated too far forward it can choke the tone. By lowering the neck angle the bridge rotates less and the guitar tone opens up. From many different experiments and measurements that rotation is accepted to be about 2deg.

So that's why this 1/2in string height at the bridge is not really a golden rule but an average. If a guitar I just built had a perfect 1/2in at the bridge but with 2.5deg rotation then I would adjust the neck angle to get back to 2deg rotation which would lower the string height at the bridge a bit. But I would rather have proper rotation which is actually meaningful than the 1/2in height which is not.
That is the best analysis I have seen posted on the subject. It needs to be a sticky.....required reading for those obsessed with the 1/2" rule.

The goal should always center around how a guitar plays and sounds, not adherence to a geometric 'norm'.
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  #37  
Old 01-26-2021, 10:22 AM
FPerezRoig FPerezRoig is offline
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Originally Posted by charles Tauber View Post
I'm not sure what you are trying to do.
If you want it, I can post the equation that I developed and use to calculate neck angle. I have also laid it out geometrically in a parametric CAD system, allowing me to change any of the parameters to see the resulting geometry.
Yes please! It would be great. If you could share the CAD file that would be awesome.
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  #38  
Old 01-26-2021, 11:26 AM
charles Tauber charles Tauber is offline
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Originally Posted by FPerezRoig View Post
Yes please! It would be great. If you could share the CAD file that would be awesome.
I'll write it up and post it to my website. I'll post the link here when it is done.

The catch with parametric CAD systems is that each uses its own proprietary modelling kernel. What that means, practically, is that exporting the model from the native authoring CAD system strips off the "intelligence" of the parametric model. What you get upon export is only the "dumb", static geometry, losing the ability to change parameters (dimensions) to alter the geometry.

Some modern CAD tools have the ability to edit model geometry without the need for the parametric data. Better than nothing, but not the same.

The models I have are currently in Fusion 360 and Onshape.

If those formats are of use to you, I can make them available. (Fusion 360 now requires a subscription to export models in non-native formats, such as STEP and DXF. Onshape still allows it for free and I can export models in those "dumb" formats.)
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  #39  
Old 01-26-2021, 01:12 PM
FPerezRoig FPerezRoig is offline
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Thank you! Look forward to reading your post and rest of your site.

Yes I have access to Fusion 360. Your model would be great to have as a learning platform. I really appreciate your contribution, thanks
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  #40  
Old 01-26-2021, 05:24 PM
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Victory Pete Victory Pete is offline
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Quote:
Originally Posted by Victory Pete View Post
One thing I have noticed, the guitar with the flat top is very open, responsive and bassy, it would be great for finger picking. I think this indicates that the top is loose, I suppose from not have any stress in a radiused top. The other guitar with a small amount of dome to it's top, is very punchy and tight, that is how I like them being a strummer.
I am going to try something different on the current guitar I am building. The top after being braced has a slight radius to it now. To guarantee it stays this way while gluing to the sides I am going to put in a threaded brace jack to keep this radius while I clamp and glue in the Gobar deck. I may simply put one on the center of the X brace or put two under the bridge with a caul I have. This way if I ended up with a top that has no radius again I can persuade it to have one. I think doing this will also put some stress into the top making it stiffer.
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  #41  
Old 01-26-2021, 05:51 PM
charles Tauber charles Tauber is offline
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Originally Posted by Victory Pete View Post
I think doing this will also put some stress into the top making it stiffer.
It doesn't.

Bending stiffness is not dependant upon stress.

https://en.wikipedia.org/wiki/Bending_stiffness

http://www.wikiengineer.com/Structural/BendingStress
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  #42  
Old 01-27-2021, 03:45 AM
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Victory Pete Victory Pete is offline
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Originally Posted by charles Tauber View Post
I appreciate science and Wiki pages but I believe that my assertion is correct. If a flat relatively flimsy soundboard is prestressed upward into an arc and then forced to stay in that arc by being glued in place, it will be stiffer. I say flimsy because the guitar which had the flat soundboard moved more from string pull making its action too high now.
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  #43  
Old 01-27-2021, 08:11 AM
redir redir is offline
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The only thing that will change the stiffness of a soundboard is if you change it's dimensions in length, width, or height. It's math, you cannot have an opinion of it, it's a solid fact

Don't confuse stiffness with strength: https://www.setareh.arch.vt.edu/safa..._strength.html

Arching has it's own physical proerties too but it's my understanding that we luthiers do it more for dealing with changes in humidity than say building an aqueduct like the Romans did with arched structures for strength.
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  #44  
Old 01-27-2021, 08:17 AM
charles Tauber charles Tauber is offline
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Quote:
Originally Posted by Victory Pete View Post
I appreciate science and Wiki pages but I believe that my assertion is correct. If a flat relatively flimsy soundboard is prestressed upward into an arc and then forced to stay in that arc by being glued in place, it will be stiffer. I say flimsy because the guitar which had the flat soundboard moved more from string pull making its action too high now.
An arch will resist deformation under load more than a flat structure. That isn’t because it is pre-stressed. It is because of the geometry.

Concrete (and stone) is relatively weak in tension. Modern Concrete structures are often pre-stressed to compress the concrete, reducing or eliminating tension within the structure when under load. By contrast wood is often weaker in compression than in tension.

The architecture of Ancient Greece predated knowledge of the arch as a structural element. Much of their architecture was a result of the limits in strength of straight stone columns and beams.

A guitar top has so little arch as to provide very little added stiffness. The arch in acoustic guitars is mostly for decreasing damage due to humidity changes.

Last edited by charles Tauber; 01-27-2021 at 08:26 AM.
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  #45  
Old 01-27-2021, 08:43 AM
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Victory Pete Victory Pete is offline
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Thanks for the replies, but I am convinced that what I am describing is of benefit for many reasons, one being tone.
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