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Proposal - to skin the inside of guitar ribs and linings with CF before closing the box, as opposed to laminated sides.
3 fold objectives.
- to make the ribs stiffer and absorb less energy from the top
- to make the box more stable under sting tension, increasing time until neck set may be needed.
- eliminates any need for side reinforcement
Thoughts/Opinions?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Interesting, for sure it would eliminate the need for side reinforcement. With care you could make it look really cool. I am not sure the CF stiffness would increase the impedance to the top much more than you get anyway from solid linings for the top. The extra mass from the epoxy and CF could help. I have trouble seeing how it would help with regard to supporting the neck under string tension.

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http://www.Harvestmoonguitars.com

I'm thinking the sides would be stiffer in an "up and down" plane, hence have more resistance to sting pull distorting the box. Like we sometimes see with CF rods bracing inside the box.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I also don't see how this would prevent distortion of the box to prevent resets. It does not take much movement for the box to cause neck set issues.

Didn't say prevent, "increasing time until neck set may be needed" meaning may slow down movement after initial distortion with string loading.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I have heard of folks laminating stuff, such as a layer of silk or Kevlar, between wood layers. CF would make sense, except for any issues involving profiling the sides and such. If you use a sanding dish for that it's moot. It would certainly be a neat way to do it; it can be hard to do a neat job with reinforced fiber layups.

Practice would help, but it seems possible just to skin the insides quite neatly.
Here is a video shows a good job of a rifle stock being skinned.
https://www.easycomposites.co.uk/learning/cover-parts-in-carbon-fibre-by-skinning

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I have worked with composites quite a bit and thin layers don't have much resistance to flexing. Not saying this approach would be useless, but I think it would not do much for slight distortions of the body. Flying carbon rod buttresses would be a lot more useful in that regard.

Supporting the ribs at each end block and loading them at the middle would give some indication, and I could easily try that before and after skinning.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Double post

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Also, a thought. The CF would not be just a thin plate because it not only is curved it also has a "rim" because it is covering the linings, bit like a shallow U channel, which might add to tortional stiffness.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I could see that adding a lot of strength.

If you laminated carbon fibre plate to your sides it should add some rigidity

I laminated carbon fibre cloth between layers of wood veneer on a guitar I built (back and sides). As I mentioned in previous posts the finished product had a "tupperware" tap tone. The finished guitar (solid spruce top) sounded quite nice so I don't think the carbon fibre hurt the tone any. It probably added a lot to crack resistance. One down side is when I trimmed the sides to rough dimension on the jointer it put a small nick in the HSS blades with every pass - definitely use carbide cutters when milling it.
From the little bit I've worked with carbon fibre and fibreglas I would agree with Barry - one thin layer may not add a lot of stiffness. I do think it could act to stop cracks from spreading from impact damage.
I may try it again in the future to see if I get the same result.

If you're after rigidity you need to get the CF toward the outside of the layup, with the wood in the middle: think 'distributed I-beam'. Rigidity in sides is not usually an acoustic issue so far as I can tell: the only part of the sides that seems to vibrate at a low enough pitch to make much difference is the 'flat' area below the waist. This could either help or hurt, depending, but I suspect has no major impact one way or the other in most cases. Structurally it should add to the 'beam' stiffness of the completed guitar, which would enhance long-term stability and raise the pitch of the first corpus ('neck') resonance, which might be a good thing.

If I were going that route I'd use a 1/4" layer of end grain balsa in the middle, with a layer of CF on either side, and whatever sort of fancy veneer on the outside (and maybe the inside) surface. With five-layer construction you'd end up with something very rigid, and not too heavy, with enough surface area on the edges to eliminate the need for liners if you wanted. I think I'd put them on anyway, but maybe not wide ones. With veneer on the inside it would be easy to put them in. The main issue would be routing for the binding... You'd need a vacuum press, of course.

A layer of CF between veneers in sides would certainly add a lot of crack resistance. 'Bullet proof' would require a much heavier structure, and hardly seems worth it to me.

Colin my first thought is to agree that this would stiffen the sides in the vertical direction. Trying to to think it through.

In terms of an h beam it would have a very deep centre member. The sideways and twisting forces though would be constrained to a degree by the joins to the top and back, if you like a sort of half h beam (do I mean an I beam?) and of course the curved shapes of the sides would help also.

I guess one could do some fairly simple tests with stiffness measurements on some strips of side material with and without a coating of cf epoxy composite.

I have this notion that I can’t at all justify, that it would be better to enclose the cf between two veneers of side wood... I suppose i’m thinking of a fully composite material rather than a couple of layers of stuff stuck together.

As an aside whilst making up TG’s falcate braces, particularly the sharply curved secondaries where I have to use 4 laminates, I keep thinking that the sheets of epoxy must surely contribute some stiffness in the vertical direction...

Anyway interested in any results if you pursue this.

Dave

I’ve made a bunch of guitars with carbon fiber sides. But the trick is CF is very strong in tension and useless in compression. So two skins separated makes a strong structure. One does very little except maybe prevent cracks.

CF also tends to get a bell like resonance unless dampened. So great for a sound board. If you want stiff dead sides (and I do) you can put extruded foam between the CF rather than wood (or just more CF). I’ve only made one like that, and I can’t tell you that it radically improved the sound. But it was a dawdle to “bend” sides that were 1/4” thick. No lining, no heat. Just a vacuum bag and some forms. Super efficient construction. Looks sharp too.

I’ve got a classical on my mind. Maybe I’ll do CF sides. Sure to piss off the purists! Epoxy glued on top will probably cause a few more burst blood vessels too.


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