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  #1  
Old 09-13-2021, 01:14 PM
JboneCapo JboneCapo is offline
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Smile Geometry and plans....

Hi all ,
Just received new plans for a L-00
Apparently the soundboard is to be completely flat with no radius.
The neck follows the body straight , so no neck angle either.

The plans say that when strung up, the bridge will bulge up 3-5mm to arch the top.

This to me seems odd.. has anybody used this method?

I'm leaning towards getting a couple radius dishes and adjusting the plans

If anyone has any thoughts please let me know
Thanks
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  #2  
Old 09-13-2021, 03:58 PM
Fathand Fathand is offline
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Which plans are you using? I built a L-00 largely from the Grellier plans, (downloaded) which show a radius on the top braces and a 28ft top radius.

Happy to send a .pdf if you need one and can't find the download site.
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  #3  
Old 09-13-2021, 04:17 PM
JboneCapo JboneCapo is offline
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Perfect , I've got them!

I was using GenOne plans but I think I'm just going to ignore their instructions and go with the gut.
Looks like I need a 28ft radius dish!

Thanks!
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  #4  
Old 09-13-2021, 05:01 PM
John Arnold John Arnold is offline
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All you need is curved cauls to glue the braces. I have never used a radius dish.
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  #5  
Old 09-13-2021, 05:11 PM
Rudy4 Rudy4 is offline
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Quote:
Originally Posted by JboneCapo View Post
Hi all ,
Just received new plans for a L-00
Apparently the soundboard is to be completely flat with no radius.
The neck follows the body straight , so no neck angle either.

The plans say that when strung up, the bridge will bulge up 3-5mm to arch the top.

This to me seems odd.. has anybody used this method?

I'm leaning towards getting a couple radius dishes and adjusting the plans

If anyone has any thoughts please let me know
Thanks
I posted a complete CAD drawing pdf for a small body 14 fret slot head that you might want to look at. The top and back plates are slightly radiused, and I think it contributes to the tone and volume. Building flat and counting on string tension to pull an arch doesn't seem like very sound engineering practice to me.

https://www.acousticguitarforum.com/...d.php?t=579732

I've played a lot of instruments over my 55 years of playing time and this one is something special.
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  #6  
Old 09-13-2021, 05:31 PM
Fathand Fathand is offline
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Quote:
Originally Posted by John Arnold View Post
All you need is curved cauls to glue the braces. I have never used a radius dish.
Please explain curved cauls, I have only glued top and back to the radiused braces with regular bar or spring clamps padding them with wood or leather but then I am only on my 3rd guitar and have lots to learn.
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  #7  
Old 09-13-2021, 07:58 PM
John Arnold John Arnold is offline
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The cauls I use were bandsawn from 2X4's, so they are 1 1/2" wide. This allows the use of a go-bar deck. If you are using deep throat clamps, all you need is a flexible strip to protect the spruce from the clamps and to distribute the pressure. The strips that I have used are basswood that is 1 1/8" wide and 5/32" thick. Any soft, flexible wood will work. You can also use them on top of the bandsawn cauls if you don't want to bother with smoothing them.
BTW, I don't radius the tone bars and I clamp them flat. String tension will automatically pull some radius in the top below the bridge.
OTOH, you do need radius above the bridge to keep the top from going concave. String tension torques the bridge. While the design of X bracing stiffens the top between the bridge and soundhole, it still helps to have that little bit of radius.

Last edited by John Arnold; 09-13-2021 at 08:06 PM.
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Old 09-13-2021, 09:52 PM
Fathand Fathand is offline
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Quote:
Originally Posted by John Arnold View Post
The cauls I use were bandsawn from 2X4's, so they are 1 1/2" wide. This allows the use of a go-bar deck. If you are using deep throat clamps, all you need is a flexible strip to protect the spruce from the clamps and to distribute the pressure. The strips that I have used are basswood that is 1 1/8" wide and 5/32" thick. Any soft, flexible wood will work. You can also use them on top of the bandsawn cauls if you don't want to bother with smoothing them.
BTW, I don't radius the tone bars and I clamp them flat. String tension will automatically pull some radius in the top below the bridge.
OTOH, you do need radius above the bridge to keep the top from going concave. String tension torques the bridge. While the design of X bracing stiffens the top between the bridge and soundhole, it still helps to have that little bit of radius.
Thanks for that
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Old 09-14-2021, 12:59 PM
redir redir is offline
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What they said does make sense though. I build a very small parlor guitar that has a dead flat top and I have built guitars as big as an L2 that had flat tops too. In either case string tension does indeed pull an arch into it. But arching the top is good for protecting it against rapid changes in RH so there's that.

I don't use a radius dish either but I do radius the braces and then simply use flat flexible cauls on the back. If you tape them in place it helps.

https://www.tiktok.com/@piusone/vide...81200673441285
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  #10  
Old 09-14-2021, 01:02 PM
redir redir is offline
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Quote:
Originally Posted by John Arnold View Post
The cauls I use were bandsawn from 2X4's, so they are 1 1/2" wide. This allows the use of a go-bar deck. If you are using deep throat clamps, all you need is a flexible strip to protect the spruce from the clamps and to distribute the pressure. The strips that I have used are basswood that is 1 1/8" wide and 5/32" thick. Any soft, flexible wood will work. You can also use them on top of the bandsawn cauls if you don't want to bother with smoothing them.
BTW, I don't radius the tone bars and I clamp them flat. String tension will automatically pull some radius in the top below the bridge.
OTOH, you do need radius above the bridge to keep the top from going concave. String tension torques the bridge. While the design of X bracing stiffens the top between the bridge and soundhole, it still helps to have that little bit of radius.
John, so your braces are flat but then they are clamped and pressed into the radiused clamping caul? Do you get any bounce back from that or does it hold that radius in place? I'm also curious if you do this for any particular reason? Does it have something to do with strength, stiffness or even RH%? OR is is it simply why bother radiusing the braces when this works just fine kind of thing?
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  #11  
Old 09-14-2021, 05:48 PM
John Arnold John Arnold is offline
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I radius the X-braces and the upper transverse brace. Tone bars are the two diagonal braces in the lower bout (traditional Martin style).
I have little faith in bending braces while gluing them to create an arch.
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  #12  
Old 09-14-2021, 07:36 PM
redir redir is offline
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Oh ok I get ya. Yeah the span there is not so great that putting a radius in those braces might not matter.
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  #13  
Old 09-14-2021, 07:59 PM
John Arnold John Arnold is offline
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On the contrary, it does matter. Those braces span most of the width of the lower bout. Making the top flat below the bridge alters the geometry, such that the bridge will not tip forward under string tension. The finger braces and the soundhole braces are the ones that are so short that a radius doesn't matter.
I glue top braces in three steps.
1) X-braces, onto radius cauls.
2) Tone bars, bridgeplate, and finger braces, all clamped flat
3} Upper transverse brace and soundhole braces. The transverse brace also uses a curved caul.

If I am notching the braces and bridgeplate into the X-braces (prewar Martin style), I swap steps #1 and #2.
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  #14  
Old 09-15-2021, 06:39 AM
redir redir is offline
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Thanks John for clarifying.
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