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-   -   I'm planning to build carbon fibre guitar (https://www.acousticguitarforum.com/forums/showthread.php?t=372446)

Tygrys 01-21-2015 08:50 PM

I'm planning to build carbon fibre guitar
 
As I have experience working with carbon and others fibre materials making format and later guitar should not be so difficult.

But carbon is not a wood. Is flatter and harder... Is just different and I believe I need use different approach to this project but let's start.

As in title I'm planning to build and one.

I often play finger style about 60% of my playing. The important for are tone and sound including high and low notes. The volume is important but not mostly important. I want "travel size" guitar, as I often walking with backpack or riding moturbike with guitar size is important. I'm thinking about something close to CA cargo but I'm not sure isn't a good idea.

Therefore I decided to ask for help.

What would you recommend as a scale length?

What depth of guitar should do?

I know that my guitar will have cut for high notes.

Thank you all for advice.

printer2 01-21-2015 09:34 PM

Sides, stiff as practical, a live back if you want more of a player's guitar rather than one to please the audience. Top, try to shoot for the same stiffness and weight as a wood top. Think spruce would be about 480kg/m3. Some look for the bridge to rotate 2 degrees from a free top to strung up.

GreenWoodworker 01-21-2015 11:04 PM

To me, it seems someone needed to find a better way to bond the carbon fiber together other than regular resin. The one i played didnt sound good, guessing it was the resin deadening it.

Question, how do you plan on making the fret board? Wood?

Tygrys 01-22-2015 02:55 AM

Quote:

Originally Posted by printer2 (Post 4322733)
Sides, stiff as practical, a live back if you want more of a player's guitar rather than one to please the audience. Top, try to shoot for the same stiffness and weight as a wood top. Think spruce would be about 480kg/m3. Some look for the bridge to rotate 2 degrees from a free top to strung up.

Thank you for advice.

Could you please explain to me what does it mean:
for the bridge to rotate 2 degrees from a free top to strung up.

And how stiff should be back in guessing stiffer then front?

Tygrys 01-22-2015 02:59 AM

Quote:

Originally Posted by GreenWoodworker (Post 4322807)

Question, how do you plan on making the fret board? Wood?

I was thinking about carbon for the fret board.

I want this guitar to be weather resistant as much as is possible.

ac 01-22-2015 08:29 AM

If possible, check models of brands out there and try them to see which size body has sound you like.

Usually, CF is layered in some way or another and different builders layer the soundboards different from each other for their own "tone". But sides and back can be CF or a less expensive CF/fiberglass mix. Rainsong and Journey have specific models that use the mixed material for sides and back to reduce cost--but many prefer the sound as well.

All the makers glue the soundboard to the top separately except Emerald. Emerald developed a unique way of building the entire guitar from a single piece of CF--so the top and even the bridge are all a solid piece intregal with the back and sides--not glued on.

printer2 01-22-2015 08:33 AM

Quote:

Originally Posted by Tygrys (Post 4322889)
Thank you for advice.

Could you please explain to me what does it mean:
for the bridge to rotate 2 degrees from a free top to strung up.

And how stiff should be back in guessing stiffer then front?

If you take a thin piece of wood and temporarily attach at a right angle to your bridge you will be able to measure a 90 degree angle. Now when you string up the guitar and have it tuned you will be rotating the bridge towards the fretboard. For from the Gore/Gilet guitar making books on wood guitars two degrees is a good target.

Might be easier to measure the stiffness of your top by measuring the deflection down when you put a weight on it. I do not have any data on that but if you google it you might find a target. Or if you use a guitar that you like you can measure it. Hope you do not mind my saying, but you have a steep learning curve to build the guitar as you want. Be prepared to do some experimenting before you start your guitar build.

It might be of benefit to you to look up classical guitars made with balsa, lattice construction, carbon fiber. Keep in mind the tension for classical guitars are about half a steel string.

Alan Carruth 01-22-2015 01:12 PM

printer2 wrote:
"...try to shoot for the same stiffness and weight as a wood top."

The problem is that CF composite is much denser than wood, and has a much higher Young's modulus. A sheet of CF that has the same weight as a wood top will be too thin to be very stiff, and one that is thick enough to have the same stiffness will be too heavy.

Back in the '70s some folks at the Catgut Acoustical Society worked out a spruce substitute using CF. After some experimentation they found that thin layers (around .002" or less) of unidirectional pre-preg tape on a cardboard substrate about 1/16" thick made a good substitute. They ran into two problems:
1) with changes in humidity the cardboard would swell and shrink, but not the CF. Eventually (a few months) the CF would delaminate and come off in ribbons, and
2) Kaman (of Ovation guitars) was following along on their research, and took out a patent before they could publish. They consulted a lawyer, who said they had an excellent case if they decided to sue, but that it would cost them a lot of money. Since they only wanted to publish a paper they opted not to. By now the patent has expired, so I think you could go ahead and try to solve the delamination issue. Maybe Nomex?

Tygrys 01-22-2015 05:56 PM

Thank you for all advices.

I'm not waring about delamination I have friends who are producing kayakswhich are used by world champions in warriors competitions (canoe polo, playboting, and long distance racing)
They already solved the lamination problem and agree to use their workshop for lamination.

Coming back to a basics for now I know that sides of guitar body must be as stiff as possible. Front the sound board thin and stiff enough so it would not deformed from string tension. Back board need to resonate well but must be stiffer then the front board. I also have idea that back and sides with integrated neck of the guitar will be in one mold.I know that I want to have cut for high notes. Bridge will be at the middle of guitar body.

But now I need advice how long scale should I use barring in mind that this CF guitar will be a "travel" guitar. From many reasons I like CA cargo guitar but those ones have short scale. I also like finger style playing so the guitar must be responsive.

What depth of guitar should do? In other words how thick the body should be and I the body should have same thickness all over or thicker at the end of the body and thinner on the neck side and if so what the difference would you recommend?

Tygrys 01-22-2015 06:03 PM

Quote:

Originally Posted by Alan Carruth (Post 4323545)
printer2 wrote:
"...try to shoot for the same stiffness and weight as a wood top."

The problem is that CF composite is much denser than wood, and has a much higher Young's modulus. A sheet of CF that has the same weight as a wood top will be too thin to be very stiff, and one that is thick enough to have the same stiffness will be too heavy.

Back in the '70s some folks at the Catgut Acoustical Society worked out a spruce substitute using CF. After some experimentation they found that thin layers (around .002" or less) of unidirectional pre-preg tape on a cardboard substrate about 1/16" thick made a good substitute. They ran into two problems:
1) with changes in humidity the cardboard would swell and shrink, but not the CF. Eventually (a few months) the CF would delaminate and come off in ribbons, and

I was thinking to use just carbon for sound board of the guitar but my question is what shell is do one layer of the strongest carbon or mix value of carbon stiffness of layer of the less stiff carbon or more ofcourse I will use the bracing

I know that I will need to try to reach the optimum construction but I'm sure that some one already done it so advice will be more then welcome.

Tygrys 01-22-2015 06:06 PM

Just to add this is long term project which I will work on in my spare time therefore me time target is to finish before 2016 summer.

Till end of May I wish to have the model of the guitar ready to make the former.

Tygrys 01-22-2015 07:11 PM

Quote:

Originally Posted by printer2 (Post 4323084)
Hope you do not mind my saying, but you have a steep learning curve to build the guitar as you want

Ofcourse I don't mind there forever I'm in this forum to take average advice in to account.

printer2 01-23-2015 10:29 AM

I assumed that being experienced with working with composites that the OP would know a solid top would be too stiff and heavy and a sandwich construction with something like balsa or a honeycomb material would be used in the core. I have a little experience with composites coming from the RC airplane hobby along with working for a time in an aerospace company where much of the time the CF is only a skin and not used through the whole part. My bad.

For what it is worth I rigged up a setup to measure top deflection and measured three guitars I have. A parlor, a 00 size, and a dred. With a load of 1280 grams on the bridge I had roughly a deflection of 0.010-0.013".

Tygrys 01-23-2015 01:28 PM

Quote:

Originally Posted by printer2 (Post 4324914)
I assumed that being experienced with working with composites that the OP would know a solid top would be too stiff and heavy and a sandwich construction with something like balsa or a honeycomb material would be used in the core. I have a little experience with composites coming from the RC airplane hobby along with working for a time in an aerospace company where much of the time the CF is only a skin and not used through the whole part. My bad.

For what it is worth I rigged up a setup to measure top deflection and measured three guitars I have. A parlor, a 00 size, and a dred. With a load of 1280 grams on the bridge I had roughly a deflection of 0.010-0.013".

Thank you for measuring the bridge area.

When I was thinking to myself friends we were more thinking to use just CF one or two layers with out any thing between.

The bracing will work instant of honeycomb or similar materials.

On sides in will use honeycomb.

Earl49 01-23-2015 05:08 PM

FWIW, my early manufacture Rainsong WS-1000 has a roughly 3/16" thick layer of urethane (?) foam sprayed on the inside of the top, which can be felt - but not seen - from inside the sound hole. It seems to cover most of the top area inside, but not the back or sides. My assumption is that the CF top was too "live" by itself and rang too long, so the foam was added to more closely approximate the damping characteristics of wood. They have since gone a slightly different route with their more recent guitars. Damping may be part of the effect achieved when using things like Nomex or balsa between CF layers. Ovation used birch veneer laminated with CF for their high-end Adamas guitars, and those were pretty good tonally.

A previous post mentioned that a homemade CF guitar sounded "dead". If you've worked with composites before, you already know that it is very easy to get too much resin onto the cloth, which would explain "deadness". In aircraft building, excess resin adds weight but no extra strength to the structure - not good. Like in aviation, I believe that Rainsong and others use vacuum bagging to force resin into the cloth matrix, allowing the use of the absolute minimum amount of resin while still getting the necessary strength. Just my semi-informed opinion here.


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