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Do you build your own acoustic guitars? Try this cool trick.....


guitarcapo
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Putting tone into soundboards and enhancing moisture absorption reluctance overall? Seems like more effort than necessary just to stay loyal to wood use in acoustics. But then, the purists would balk at the departure from the use of virgin materials as they would using carbon fiber. I think the days of using wood are numbered as sustainable materials are tonally evolved.

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What I would like to see is a stocking distributor (Stew-Mac?) of graphite components consisting of the usual constituent parts of a guitar, related tooling and structural adhesives, flock, cloth, etc. I'd feel much more confident as a first time builder, being experienced in composite structures repair (aircraft), and would probably enjoy the process much more than I would if relegated to the use of woods alone. My ROI would be the recreational part of the build itself. Tone? Sound hole acoustic emulator pick-ups are cheap.

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Tone? Sound hole acoustic emulator pick-ups are cheap.

 

If you go the GRP way, you will have a heavy dead ... thjng. And you would need a hex pickup to get some ... sound.

CF is a different kettle of fish. As long as I don't have at least access to a vacuum and autoclave, I don't see no way to even touch CF.

Materials as in CF sheets and resins are available on Amazon .... but not the autoclave needed.

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The autoclave is essential for structures requiring complete evacuation of entrained gases that, under the right atmospheric conditions, could expand and cause delamination or weaken bonded points. That would be predominantly structures frequently exposed to adiabatic changes, like aircraft transitioning from sea level pressure and temps to altitude conditions and back again, repeatedly. The guitar is pretty much exempt from that exposure.

 

I'm talking about making your basic guitar shape minus all the compound curves found on stuff like Emerald's products. That only requires the basic molds found in wood guitar making. The only difference is one only has to hand lay-up wetted cloth over the molds and then let them cure. Wood must be forced around them, water softened and heat dried. Wetted CF doesn't need that much work but it would benefit the guitar to use inside/outside molds pressed together with the wetted cloth between to force the excess resin out. That would leave a shaped portion of the whole structure, like one side, that's stronger and much lighter than wood. An entire box, minus the top, could be made that way. The mold has to be polished and prepped with a mold release but that's SOP for any composite fabrication. Just the idea that I would not have to contend with wood sawdust is a plus. And, I would not have the tree police aspect to squirrel around and/or show my small hairs to.

 

 

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[uSER=168471]Idunno[/uSER] I've seen a lot of automotive CF getting the autoclave treatment, too. It's not only because of adiabatic changes but also to prevent weaknesses from delamination due to air bubbles et al during the construction. Emerald uses a balloon type system to ensure lamination with positive force. In a guitar, you want to have the thinnest and lightest soundboard you can get, so you don't want to waste material and resin. Otherwise, one could get just flat already laminated CF sheets and treat them like wood for top and back. Sides, though, have to be laminated into a form.

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[uSER=168471]Idunno[/uSER] I've seen a lot of automotive CF getting the autoclave treatment' date=' too. It's not only because of adiabatic changes but also to prevent weaknesses from delamination due to air bubbles et al during the construction. Emerald uses a balloon type system to ensure lamination with positive force. In a guitar, you want to have the thinnest and lightest soundboard you can get, so you don't want to waste material and resin. Otherwise, one could get just flat already laminated CF sheets and treat them like wood for top and back. Sides, though, have to be laminated into a form.[/quote']

 

Of course you're right, but an autoclave is not wholly necessary to achieve the desired results adequate to a guitar build. Compression methods work fine for flat and single plane curved (sides) lay-ups. The squeeze of compression drives out unnecessary resin as well as entrained air. What the autoclave provides is vacuum and heat. It's an airless oven. Because the resins used are agroscopic heat is needed to drive out moisture that can create huge problems later. Witness the Hawaiian airlines B737 plane that lost its crown skin, ejecting a flight attendant, but landed safely with the remaining occupants. The cause of that was cold-cured polymers used between over-lapping aluminum skins at the riveted joints. The moisture in the polymer eventually corroded that joint and it finally burst open under normal cabin differential pressure. That lesson put all aircraft builders on a course of using heat cured polymers in critical areas, and prompted a series of national authority mandated checks of the world's aging fleet still is use. But, again, a guitar does not require that kind of thoroughness to build it and see it last well beyond the life expectancy of any wood guitar.

 

I think that traditional ideas are thwarting a concerted effort to extract good tone from polymers in the same manner standardized black paint stopped paint manufacturers from developing colors for cars. Henry Ford told everyone they could get any color they wanted as long as it was black and the world coalesced. No demand, no research. Plus, polymer use is not for just anyone as developed skills are needed. One doesn't just walk right in and start making composite guitars, and there's no standardized data for doing so. Probably the closest thing would be the U.S. FAA Advisory Circular for Airframe Maintenance (AC-43.13 1B/2B) that covers the basics and a little more in the detail a beginner could find helpful. I keep a copy of it in my library at work for training new hires. Other industry references are available but they're similarly basic in nature. So, current builders are not going to shift from their use of wood materials very easily to get the ball rolling in composites. But not just any builder will do. What we need are builders who have well developed ears to take on the composite challenge to give it the research it needs.

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The beauty of CF is' date=' that with proper direction of the weave, you can build guitar tops that don't need any secondary reinforcements like bracings.[/quote']

 

Exactly, but the compromise would require some experimenting under compression/tension loading to arrive at a best sound/strength sound board.

 

The top dynamics of a guitar place the outside surface of the soundboard under compression and the inside surface under tension loads. The traditional x-brace prevents the inside surface from being pulled (stretched) across its span and the shape of the bracing (triangle - strongest geometric shape) inhibits torsional (bending) displacement.

 

If a simple truss is placed at the torsional fulcrum, which is the weakest part of the top traversing the sound hole, the traditional sound attenuating braces would be unnecessary allowing sound to resonate omni-directionally from its source, which is the bridge, in a truer drum-like manner. Wood simply doesn't have the workability, strength to weight ratio, rigidity per identical cross section nor the temperature/moisture stability under all meteorological conditions that composites do.

 

Kaman was onto something when it enterprised composites through Ovation with the composite bowl. It retained the wood top in lieu of taking the next engineering steps towards tonal equivalency with wood and, ironically, it set the stage for not exploring the tonal qualities of composites. It fell short of impressing everyone with superb sound so it wowed them with novelty.

 

Yes, Howard, this is the correct forum. Just trying to move it past the past a bit.

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