Carbon Graphite sound boards

[ken cierp]

Carbon graphite violins and cellos get rave reviews from pro musicians in double blind comparisons. I am thinking making a sound board mold would be pretty simple -- so wood body CF top might be killer. Any thoughts?

[Dave Bagwill]

I don't know anything about working with CF as a top. Is it material one can thin, as we do wood? Does it have the same 'pumping' capabilities as wood, I wonder?

I would be all for trying it if I would not have to re-tool, and the safety risks are equivalent, and the price about the same as good wood. As Brian Burns says, you can never have enough good wood. <wink>

[Hans Mattes]

Sounds very interesting. Some questions come to mind.

> bracing/stiffness related:
- would you use a single layer of woven CF? how tight a weave? or would you build up multiple layers? Criss-crossed?
- would you dome the soundboard?
- would you build it to a thickness that didn't need bracing?
- if you decided to use bracing, would you incorporate CF bracing into the layup or would you glue (epoxy?) spruce bracing to the backside of the CF soundboard?
- would you use a wooden bridgeplate or would you make the CF thicker behind the bridge? Or?

> esthetics related:
- would you incorporate a rosette? How?
- how would you finish the edges of the sound hole?
- what about binding? If done traditionally, how does CF rout? Does it dull the router bit excessively?
- would you put a finish on the completed top, or leave the CF as it came from the build?

I'm NOT trying to confuse, diffuse, or deter this project. I think it sounds very cool and I'm very interested in following whatever comes of it, with the intention of trying something like this myself.

[ken cierp]

Based on this blurb from Rain Song --- it seems that their sound board design is free of any conventional bracing and the layering pattern is the magic. That is exactly what I had in mind, so its easy to see why a CF top could be incredibly light weight and responsive. This is why the concept has my attention, essentially if the top can resist the pull of the strings and the bridge stay glued to the soundboard all the other structural concerns Hans listed simply do not matter, since the plate acts as a diaphragm the full extent of its boundaries.

http://www.rainsong.com/sound.html

[Dave Bagwill]

Well it makes a lot of sense. If the top is 95% of the sound of the guitar, it would be possible to build very consistent instruments. I wonder if there is a Red Spruce equivalent, or a Sitka equivalent, or Cedar etc, depending on the weave and the layering? Are bindings necessary? I would think not.. or thinning of the perimeter? And no braces. No tap tuning, no thinning in strategic areas - there's a lot I don't know about this.
Is the stuff available commercially?

[Hans Mattes]

A range of flat carbon fiber sheets are commercially available. https://www.rockwestcomposites.com/plat ... bric-plate is fairly representative. They are available in various weaves and in thicknesses of 0.030", 0.050", 0.060", 0.090" and thicker. Prices for a 24" x 24" sheet range from around $120 to $170, depending on thickness and weave. 24" x 48" sheets cost almost twice that much, but could yield 3 tops.

If we wanted to follow Rain Song's brace-free direction, we'd need to decipher the secrets of layering and weave. That could entail a good bit of experimentation. I thought about computer modeling (FEA or ???) but I don't know how to quantify the goals of a soundboard. And the Rain Song top is domed. As far as I know, domed sheets are not commercially available. So truly following the Rain Song direction will require laying up the carbon fiber top ourselves. My limited exposure to vacuum bagging of fiberglass makes me very reluctant to go down that path.

While recognizing the accomplishments of the Rain Song design, we might be better off by using a very thin (0.030") carbon fiber top and epoxying on light, slightly-domed braces that could then be thinned as necessary after the box is closed. Lattice bracing may be attractive.

As far as binding (both the top/side joint and the edge of the soundhole), it may be difficult to give the cut edge of a carbon fiber sheet an appropriate finish when using woodshop tools. I've made a bridgeplate by laminating carbon fiber sheet to rosewood, but the edges were not exposed to fingers, so the finish wasn't critical.

Regarding construction techniques, some experimentation would be required. It might be necessary to use epoxy for all attachments to the top (sides, bridge, bridgeplate, and, maybe, fretboard extension). Some tests on scrap pieces of carbon fiber sheet would be useful.

When I put this all together, I'm not as enthusiastic about a build with a carbon fiber top as I was earlier. There are a lot of unknowns that will have to be worked out -- consuming considerable time, cost, and effort -- and then we'll have a recipe for making a guitar with a carbon fiber top and wooden back and sides. I have no confidence that this will be better than the guitars we make now with wooden tops and wooden back and sides. An all-carbon fiber guitar has the advantage of immunity to temperature and humidity issues, but with wooden back and sides, that immunity is lost. And the gains to be achieved with a carbon fiber top are unclear. Repeatability? Maybe. Desirability? Not so clear.

So, at this point, I'm planning for my next build to have a wooden top.

But I would love to be convinced otherwise.