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Laminated braces - what impact?
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=25707		 Page 1 of 1
Author:  Corky Long [ Wed Jan 27, 2010 8:38 am ]
Post subject:  Laminated braces - what impact?
I'm interested in experimenting with laminated braces, a la Larson Brothers. I'm wondering whether anyone here has worked this way before, and what you experienced with the final product? My thought is spruce (80 thousandths) , rosewood (80 thousandths) , spruce (80 thousandths), and braces about .625 thousandths, before scalloping. Glue is hot hide glue.

Any insights welcome
Author:  Corky Long [ Wed Jan 27, 2010 10:43 am ]
Post subject:  Help : Laminated braces - what impact?
Bump -

No responses? Come on, I know within this group, someone has a point of view. 8-)
Author:  JJ Donohue [ Wed Jan 27, 2010 11:00 am ]
Post subject:  Re: Laminated braces - what impact?
Corky...I have not laminated spruce with rosewood. I have laminated X-braces with .020" CF and found the stiffness to be significantly increased. There are 2 reasons I did this:
1) To provide for a lighter but stronger superstructure.
2) To assure that the dome is maintained over time.

So far, after a year of doing this with 2 guitars, I have been pleased with the tonal results. Maintaining the dome will need to wait for a few decades and compare to those guitars that have standard bracing.
Author:  Michael Dale Payne [ Wed Jan 27, 2010 11:09 am ]
Post subject:  Re: Laminated braces - what impact?
Corky I am with JJ here I have laminated braces on a few guitars with CF but I would not want to laminate with rosewood. It would seem to me to only add weight and maybe even reduce energy transmittal. The only good thing I can see that you would gain from using rosewood as a center laminate is a pleasing appearance. Now I do use cut-offs from my laminated neck blanks to make rim side bracing. But I do that only for the look.
Author:  Corky Long [ Wed Jan 27, 2010 11:15 am ]
Post subject:  Re: Laminated braces - what impact?
Thanks, Michael and JJ. Appreciate your input. I'll let you know how it goes.
Author:  bluescreek [ Wed Jan 27, 2010 11:40 am ]
Post subject:  Re: Laminated braces - what impact?
i do admit to being traditionalist but I can see the benifit of laminated bracing. I do agree CF is outstanding material. When you want to attain strength and stability this will do it. I know many high end builders use this method .
Author:  Parser [ Wed Jan 27, 2010 11:54 am ]
Post subject:  Re: Laminated braces - what impact?
I don't know why you would use any rosewood for the top braces (outside of the bridge plate). Rosewood has a lower stiffness to density ratio and as such, would result in a heavier, and more likely, less responsive top. If anything, I would think you would want to look at carbon fiber & such.
Author:  Christian Schmid [ Wed Jan 27, 2010 12:06 pm ]
Post subject:  Re: Laminated braces - what impact?
Sorry for the hijack...but it's sort of related.

I guess you use epoxy for laminating the spruce-CF-spruce brace? How does CF work? Can you shape the braces just like any solid spruce brace with chisels/planes/sandpaper?

thanks, Christian
Author:  Laurent Brondel [ Wed Jan 27, 2010 12:18 pm ]
Post subject:  Re: Laminated braces - what impact?
High end Larson Brothers guitars had spruce/Braz or ebony/spruce laminated bracing and are praised for their tone. A couple of contemporary builders are making replicas. Maybe look up their websites for more info.

I think any rosewood would work very well and the (minimal) added weight may be a benefit. Laminating will make any sandwich stronger than a solid piece, and will also increase stability and the tendency to distort.
It all depends what tone you're after.

CF is great, for sure, but it's hard on edge tools and on lungs.

Edit: Actually I do think laminating top braces can be a benefit for large guitars, not so much for smaller boxes.
Author:  Alexandru Marian [ Wed Jan 27, 2010 12:33 pm ]
Post subject:  Re: Laminated braces - what impact?
I've heard about a lamination giving more strength but a test I did laminating two spruce braces did not find any of this. The initial pieces had different deflection measurements, and I recorded them. Then glued them up, trimmed to the original width and weight, tested again and it scored a hair less than the less stiff initial piece! If not better, I would have expected it to at least land in between the two initial results, but I can say the differences were small and likely within the error margin of the deflection setup.

To sum it up, my test did not reveal any stiffness gain from laminating.


In some cases a brace with a thin rosewood strip might not end up heavier than a solid spruce one, if the solid is a heavy spruce and the one in the lamination is lower than average.
Author:  Laurent Brondel [ Wed Jan 27, 2010 12:48 pm ]
Post subject:  Re: Laminated braces - what impact?
Alexandru Marian wrote:
IThen glued them up, trimmed to the original width and weight, tested again and it scored a hair less than the less stiff initial piece!

I am not understanding your method…

I routinely laminate parts, from bridgeplates to sides to necks. There's no need for deflection tests (for me) as the difference in all cases is glaringly obvious.
A case in point is sides: 2 x .040" laminated sides are so much stiffer than a single .085" side, with whatever material. Laminated necks (by reversing the grain direction, which should be done with braces as well) are stiffer than a single piece neck at equal dimensions by a great deal, and more resistant to twisting as well. In some laminated necks the truss rod has almost no effect at all.
Author:  woody b [ Wed Jan 27, 2010 1:06 pm ]
Post subject:  Re: Laminated braces - what impact?
I laminate my upper transverse brace, spruce/rosewood or maple/spruce, but I don't consider it to be a "tone" brace. I haven't used carbon fiber anywhere except in necks. I read that the stiffness to weight ratio of carbon fiber is actually slightly lower than most spruce, but it's memory is better. <<<<<<<< I read that, I don't know, or have any actual experience to back it up. I always try to make it clear when I post something I read, as opposed to something I learned from actual use.

I don't plan on changing the way I brace, but I may try CF in my UTB sometime.
Author:  truckjohn [ Wed Jan 27, 2010 1:24 pm ]
Post subject:  Re: Laminated braces - what impact?
There are a couple builders who laminate braces out of thin Spruce "slats." There are several good reasons.
1. You don't have to sand braces to match the dish/profile... the slats are pliable enough to form to the dome.
2. You don't have to cut a slot for the X -- they just overlap 1 side, then the other so that the X doesn't have any gap.

Overall, I think there are some benefits and some difficulties with doing it. It seems to work just fine.

Go for it.
Author:  bluescreek [ Wed Jan 27, 2010 1:46 pm ]
Post subject:  Re: Laminated braces - what impact?
These lamination's are usually a spruce in orientation with a "stiffiner" ply in the center. This makes the brace very stiff , much like plywood. Of the builders whose guitars I have handled , JJ Donahue Mario and a few others , the most common ply seemed to be Carbon fiber, but I know rosewood and ebony have also been used. The advantage is you increase the stiffness considerably and this allows you to make a stronger brace with less weight. This allows you to remove some mass that isn't needed.
They are very stiff will not just conform to a disk. Of the ones I used I do admit they do get stiff and will need to be mechanically shaped. I know that a ply lamination can influence the strength considerably . I agree while it is a contemporary technique I can see the usefulness with traditional applications.
Author:  Alexandru Marian [ Wed Jan 27, 2010 2:00 pm ]
Post subject:  Re: Laminated braces - what impact?
Laurent,

I made two identical size QS spruce braces, tested them, then glued them side by side and trimmed back to the original size of a single brace. Same as in a laminated QS neck or Larson brace, but without the center insert.

It is definitively not the same as laminating sides on top of each other and bending them lengthwise. It does make sense such ply is stiffer.
Author:  Haans [ Wed Jan 27, 2010 3:11 pm ]
Post subject:  Re: Laminated braces - what impact?
Well, I use either rosewood, African Blackwood, or Cocobolo and it just works fine for me. Use HHG to glue 'em up. Here's a old Larson 6 pattern and my 12 string bracing.

Image
Author:  Laurent Brondel [ Wed Jan 27, 2010 4:30 pm ]
Post subject:  Re: Laminated braces - what impact?
Haans, that looks way cool.
How wide is the lower bout on the Larson 6?

Alexandru, I am not doubting the result of your test, it just doesn't match my experience.
I bet if you re-do the test with a 30" x .250" 4sawn spruce bar that you cut in half ( 2 x 15" long braces). Mark where they were cut and measure the deflection of each. Then plane both to .125" and glue them together, but reverse the grain (like a bookmatch but from the end grain), you'll find a subtantial difference.
Author:  Jeff Highland [ Wed Jan 27, 2010 4:58 pm ]
Post subject:  Re: Laminated braces - what impact?
A few comments from an engineering viewpoint.
Lamination of itself does not OF ITSELF increase stiffness.
Put a pair of spruce 2x4's together and you just double the capacity
However, in typical luthiery situations lamination has big advantages

Lets look at them one by one

Laminated sides will gain stiffness and split resistance from both the slight mismatch of grain direction and from the impregnation of the thin wood with epoxy or other glue/adhesive.
Laminated bridgeplates will benefit likewise.

Necks laminated with a centre lamination of stiffer wood (say rosewood or maple in the centre of mahogany) benefit from having that stiffer wood at the extreme fibre location at the back of the neck while most of the strip is cut away for the truss rod slot. this gives an increase in stiffness with very little weight gain.

If your just use a two piece neck, you do get an increase in stability and twist resistance through quasi-bookmatching the grain directions.

Rectangular braces laminated with a centrestrip of rosewood or carbon fibre are not the most efficient arrangement for stiffness/mass because much of the carbon fibre is located near the neutral axis.
However if your braces are carved to a triangular shape rather than left rectangular, you are leaving the stiffer carbon fibre or rosewood at the "extreme fibre" location and this will be significantly stiffer than a plain spruce brace carved to the same crossection.
Author:  Alexandru Marian [ Wed Jan 27, 2010 5:05 pm ]
Post subject:  Re: Laminated braces - what impact?
My test samples were shorter, same as what I would use as blank for a fan brace - it is the only thing where i could use increased stiffness/weight. 5 inches beam length, a bit of .25 width. I will try flipping 1 too, but I will only use 100% QS and split wood with zero runout, it should be the same thing. I'll get back tomorrow with the result.
Author:  Haans [ Wed Jan 27, 2010 7:03 pm ]
Post subject:  Re: Laminated braces - what impact?
Laurent, both are a 15-1/4" modified Stahl shape box.
Author:  Howard Klepper [ Thu Jan 28, 2010 12:58 pm ]
Post subject:  Re: Laminated braces - what impact?
What Jeff said.
Author:  Corky Long [ Thu Jan 28, 2010 3:55 pm ]
Post subject:  Re: Laminated braces - what impact?
Jeff Highland wrote:
A few comments from an engineering viewpoint.
Lamination of itself does not OF ITSELF increase stiffness.
Put a pair of spruce 2x4's together and you just double the capacity
However, in typical luthiery situations lamination has big advantages

Lets look at them one by one

Laminated sides will gain stiffness and split resistance from both the slight mismatch of grain direction and from the impregnation of the thin wood with epoxy or other glue/adhesive.
Laminated bridgeplates will benefit likewise.

Necks laminated with a centre lamination of stiffer wood (say rosewood or maple in the centre of mahogany) benefit from having that stiffer wood at the extreme fibre location at the back of the neck while most of the strip is cut away for the truss rod slot. this gives an increase in stiffness with very little weight gain.

If your just use a two piece neck, you do get an increase in stability and twist resistance through quasi-bookmatching the grain directions.

Rectangular braces laminated with a centrestrip of rosewood or carbon fibre are not the most efficient arrangement for stiffness/mass because much of the carbon fibre is located near the neutral axis.
However if your braces are carved to a triangular shape rather than left rectangular, you are leaving the stiffer carbon fibre or rosewood at the "extreme fibre" location and this will be significantly stiffer than a plain spruce brace carved to the same crossection.



Jeff - Thanks!! That makes perfect sense.
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