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Advice on parlour bracing?
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Author:  Daniel M [ Thu Feb 09, 2006 9:55 pm ]
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I'm planning a parlour guitar for my next project & would like some advice (Pics would be great) On how light I can safely go with the top bracing.
The first of 2 of these guits will have Brazilian stumpwood B&S & a coarse grained, but very stiff & resonant Engelmann top. The second will be Koa / Engelmann
The braces will be Shane's Lutz Spruce.
I have access to an early 20th century Washburn to copy, but it is ladder braced & I will probably do a traditional X.
Any advice on top thickness would also be appreciated.
Thanks in advance, Dan.
Author:  tippie53 [ Fri Feb 10, 2006 1:15 am ]
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    Lets do X bracing 101
     All X bracing is laid out by scale length. The first thing you need to know is the scale length and the position of the fret attachment.
One you know the attachment you mark the center on the top and the placement of the neck block. To this line ad the thickness of the side set.
     With your fret joint position known place the fingerboard on the top with the proper fret in place. You can now measure the scale postion from the nut to the saddle postition. Make a mark .
    Square this mark from your center line and place your bridge so the 1st string saddle location is on this mark. Draw your bridge onto the top at this location after you square and center it.
     Place your X bracing so the catch the lower corner of the bridge. I like the X brace to hit the lower corner with the rest of the bracing being free of the bridge. This way the torque of the bridge is all place on the largest part of the bracing.
       The bridge plate should be 1/8 larger than the bridge. To plot the tone bar I like the 1st tone bar to me right off the lower edge of the plate. ( Aps 2 1/4 inch from the point on the X brace where the front of the plate is.
     the finger braces will pe place at 1/2 the length of the bridge plate where it touches the X brace. This will form the W truss. This is what helps to control the rotational forces of the bridge applied to the top.
    That should cover the X , the travers and popsicle fit in the normal places.
john hall
Author:  Daniel M [ Fri Feb 10, 2006 5:25 am ]
Post subject: 
Thanks John; I do my basic layout pretty much as you describe.
I am interested in getting an idea of what the minimum X brace & upper transverse brace dimensions might be.
I usually build my bracing "scary light" & leave the top a bit on what might be considered the heavy side.
I figure, to get some punch with a really small bodied guitar, I will have to go quite thin on the top. I can "intuit" (is that a word?) how light to make the braces, but it would add to the comfort zone to hear others experience.
Author:  peterm [ Fri Feb 10, 2006 7:03 am ]
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I think a smaller guitar can afford a lighter bracing that a heavier guitar!
Author:  tippie53 [ Fri Feb 10, 2006 11:20 am ]
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      Bracing is just that. bracing. Size is not a concern stress is. You would be surprsed at the stresses . I wouldn't go under the 1/4 width. 9/16 height.
     Bracing will contribute a few things to the guitar. The headroom , or the abount of stress you can put on while playing without tonal sacrafice. To light and you have a guitar that isn't balanced and will not be clear to heavy and you will suffer with lack of volume.
    So you need to go with a balanced structural brace.
I think you will do well with the bracing I described. This has been a standard for many generations
John Hall
Author:  BruceH [ Fri Feb 10, 2006 3:54 pm ]
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Hey Dan,

I just finished a redwood parlor a couple of months ago. It was my third, so take this with a grain of salt, but here is what I learned:

The top needs to be thick enough in the bridge area to resist the twisting of the bridge caused by string pull. In my attempt to achieve the perfect finish I sanded the top back to bare wood a couple of times and I didn’t realize how quickly the redwood sanded. As a result, my top is really thin (I even cracked it during French polishing), and I can see where the bridge is distorting the top. The braces are holding firm, but the top is distorting. I had to put in another brace behind the bridge to get it to keep it from imploding. It is not seen in these pics, but is another tone bar that runs from the bridge plate to meet the normal tone bar. My top seems to be stable now, but I’ve got a lot of imprinting. As a result of this experience, the next time I’ll keep the center of the top a normal thickness and only thin the outer edges of the top. Also vitally important that the lower edges of my bridge don't fall over the x- braces, but are instead a little aft. This contributes greatly to the top's distortion.

My bracing for this top was ? wide. Here are a couple of pics.


Author:  David Collins [ Fri Feb 10, 2006 5:31 pm ]
Post subject: 
I find it useful to think of the most influential bracing on a guitar being
the sides. In other words I feel the rest of the bracing should be designed
with the sides, or "perimeter bracing" in mind, and look at the pattern as
a whole. From that point, I would say that a smaller body or tighter waist
guitar can and perhaps even should have the bracing sized and layed out
quite differently from a dreadnaught. One example is that I prefer a wider
100 degreeish "X" angle on larger bodies, while approaching around 90
on a parlor.

That said, I also look at the structural concerns of bracing taking only a
slight priority over tonal concerns. I have seen many builders try to build
lighter with the idea that they will get better volume and bass. While this
can often be true, they also often end up with a loose, floppy and
shapeless tone. So much of the bracing is not just there to keep the top
from collapsing, but to strategically control the top from getting too
unruly. So even though I would argue that you could afford to go lighter
in regards to structure, you should be carefull not to go too far.

I've always liked the old Gibsons with the tall and narrow bracing. The two
shoulder braces and X braces were typically 1/4" by about 9/16" (then
scalloped), while the tone bars, wing braces and soundhole braces were
barely 3/16" wide. And on the earliest jumbos they used three of these
narrow tone bars with excellent results.
Author:  tippie53 [ Sat Feb 11, 2006 12:50 am ]
Post subject: 
   That is the beauty of the art of luthiery. I agree on the wider bracing and all my bracing is placed so I have a wider X. I use about 95 degrees. I hate to 90 degree angles in guitars.
    The bracing is still handeling a load with the top as the string stress is still there. Bracing height and wight should still be designed with these stresses in mind.
      I will use only one finger brace and tone bar on smaller bodied instruments. David LePlante of the New York String Museum gave me an extensive lesson on this at Last years ASIA Symposium. He is one of the nations top experts on bracing and old guitars.
John Hall
   
   
Author:  guitarjtb [ Sat Feb 11, 2006 5:20 am ]
Post subject: 
Dan,

I don't have much experience with parlor guitars, but here is a link to some old bracing patterns.

http://www.burkettguitars.com/oldtop.html

If you scroll down the page, the last sample is a 1930's Gibson L-00. The lower bout on this one is a little under 15". You can get an idea of size of the bracing from this. The width of these at the widest point is a 5/16" and they taper in at the ends. The height at the tallest point is 9/16" and they taper off from there. The angle of the X-brace is approx. 85 degrees. Since a parlor will be smaller, the braces could have less mass than this. I don't think I would go much smaller, however.

The relationship of the bracing to this one's soundhole is distorted. Someone enlarged the soundhole to 4 3/4" before I got it. Not for sound, I think they were robbing the soundhole purfling.   Pardon all the editing, but I went to my shop to check the measurements.

Good luck.James Burkett38759.5784375
Author:  Daniel M [ Sat Feb 11, 2006 7:09 am ]
Post subject: 
WOW... Thanks guys! That was exactly what I was looking for.
David; You put my recent thinking into word very clearly. Considering the sides as the main structural member really helps when considering the stresses involved.
Now I can't wait to get started.
Cheers!   Dan
Author:  David Collins [ Sat Feb 11, 2006 10:36 am ]
Post subject: 
James, it's interesting to see just how inconsistant the Gibson production
was. The '35 L-00 I have in the shop right now has a 91 degree X angle,
and there is no taper to the width of the brace. The X braces are 1/4" and
the tone bars, wing braces and soundhole braces are 3/16" from end to
end. After reading your post I had to go double check, but that's how this
one is.

Consistancy never was one of Gibson's strong points, but I suppose that's
part of thier charm.

On a side note, it looks like the 35 L-00 was a case of top over the
dovetail? After pulling the neck on the one I have now, I feel a little more
motivated to keep track of when they were doing this.
Author:  guitarjtb [ Sat Feb 11, 2006 1:29 pm ]
Post subject: 
That's right, David. If you ever find 2 Gibsons that are the same, it was probably a mistake.

I'll double check the X brace angle on mine.
Author:  guitarjtb [ Sat Feb 11, 2006 2:08 pm ]
Post subject: 
My mistake, David. The X on this one is 92 degrees. Like a dummy, I was going from memory in the other post.
Author:  John Mayes [ Sat Feb 18, 2006 10:40 am ]
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I normally go one lower face brace and one finger brace on each side.
The finger braces coming off the middle of the bridge plate
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