Laminated and Carbon Fiber Enhanced Bracing

[scamp]

Starting to think about my next project ( just finished my Nautilus guitar attempt ).
Want to do something a bit more creative vs just copy an existing design so I have been investigating various bracing methods/technology that might produce a better result. Soon discovered that guitar bracing can be a rat hole you can easily get lost in. At this point still don't know what I want to do but as part of this process I think I discovered a few things that would be worth sharing.

1) Many bracing options I am considering require curved braces. A typical way to do this is to use thin layers of spruce and make a laminated brace by gluing the thin layers together in a caul. I used this method in my Nautilus guitar design.

Laminated Brace Layers.JPEG

There I used 6 layers, each 0.04 inches thick, to make a 0.24 inch thick brace. So... I decided to make a straight brace using this method and test it to see how much weight was added by the epoxy ( vs a solid 0.25 inch wide spruce brace ) and if the lamination added any stiffness by testing displacement under load.

Brace Displacement.jpeg

In the end the laminated brace weighed about 20% to 25% more and the stiffness ( displacement under load) was the same. An interesting and somewhat surprising result. I expected an increase in weight but also some improvement in stiffness. Bottom line is using curved braces made this way probably still makes sense but there is a small weight price to pay.

2) Another bracing option I have been considering is spruce braces using carbon fiber threads epoxied to the top and bottom of the brace to add stiffness ( as used by Trevor Gore in falcate bracing ). So... I bought some carbon fiber and made some test braces to measure increased weight and stiffness.

IMG_0522.JPEG

Again interesting results. A 7.6mm high by 6.1 mm wide spruce brace with carbon fiber epoxied on top and bottom had a weight increase of 12% vs a solid spruce beam of same dimension. The stiffness of this beam under load improved by about 25% vs a solid spruce beam of same dimension. Not a huge amount. More interesting is when I measured the height of the beam with the carbon fiber added it increased the height of the beam from 7.6 mm to 8.3 mm. It turns out that the stiffness of the beam is proportional to the 3rd power of the height. So an increase of height from 7.6 mm to 8.3 mm with a spruce beam ( no carbon fiber) represents an increase in stiffness of about 25% . Bottom line, at least from my experiments, is adding carbon fiber to the braces doesn't add much. It may improve long term creep ( for bracing under extreme stress ) but given it didn't have much effect on stiffness I have some doubts.

Just want to emphasize that these results are from my experiments are the best I could do and could be wrong but I thought I would pass them on as they might be useful.

Regards

[rcnewcomb]

Have you looked at or tested any of the methods for carving holes in braces to decrease weight? Examples are from Kevin Ryan (Fretboard Journal),

eo_bracing_1-1.jpg

and on Martin's GPE Inception

Screenshot 2026-02-11 115425.png

[scamp]

Not yet but it’s on my list to investigate. One thing I’m concerned about with this method is not just weight and stiffness but also structural integrity. At what point does the brace break under load with holes like this. Something to consider.

[scamp]

Took a closer look at this bracing to see what makes sense and what to test.
A few things come to mind.

1) It seems like the only possible purpose of the holes is to reduce the weight of the braces while both maintaining the stiffness and structural integrity . You would think lighter would be better so on the surface it seems to make sense.

2) I can't understand why Martin would use hexagonal holes instead of round ones. Seems like the sharp points would cause stress concentrations. Probably OK for the back braces, tone bars etc but what about the load bearing braces? Don't understand. Did they do it because it looks cool?

3) On both the Ryan and Martin designs it seems like the brace heights are very high ( relative to a conventional design ). For the major load bearing braces ( especially the x-braces in the upper bout ) they are very high. Since stiffness is proportional to the 3rd power of the brace height it suggests this bracing is very stiff. So why do this? I can only guess it was done to increase the structural integrity of the brace so it can take the load ( given the holes in it ). If that's the case, seems like there might be minimal weight reduction vs a standard design and the top is stiffer which isn't great. Can't understand why they would make the non-load bearing braces taller. Do the holes decrease the stiffness that much? Bottom line is I am confused.

4) I have no idea why Martin put holes in the Traverse brace in the upper bout. Seems like this part of the top is very stiff and not moving anyway. Why make this part lighter?

Anyway... lots of questions and not a lot of answers. I might do some experiments to see how much the stiffness changes because of the holes and also how much it effects the breaking point of the beam.

[rcnewcomb]

I'm unsure of Kevin Ryan's engineering background.

I think Martin should have hired a mechanical engineering consultant with a deep understanding of statics, trusses, and wood properties. My guess is that they went with the hex holes because they were easier to machine. I doubt that anyone worked the math.

Screenshot 2026-02-12 082714.png

[scamp]

I'm unsure of Kevin Ryan's engineering background.

I think Martin should have hired a mechanical engineering consultant with a deep understanding of statics, trusses, and wood properties. My guess is that they went with the hex holes because they were easier to machine. I doubt that anyone worked the math.
Screenshot 2026-02-12 082714.png

You may be correct but it's hard to believe Martin would undertake a new design like this without having an expert on structural mechanical design and acoustics.

What is also perplexing is the routed channels they put in the top around the braces. Seems like this would make the tops weaker and prone to cracking along the grain. I was thinking it might cause a discontinuity in the impedance of the top causing high frequency reflections that change the acoustics somehow but who knows.