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I was just looking at Jim's new solera - work of art - and noticed that he and a lot of others laminate their transverse braces with carbon fiber. I understand the principal; make the brace stronger. But I don't see that the brace is smaller or perhaps lighter by any significant eyeball measure.

So, is it simply for strength and structural integrity?
Does it allow you to make your tops thinner with the same cross grain support?
Does it change the sound transfer? If the people I see using it are using it, it must be for a good reason, and I like to follow smart people, or at least learn from their smart ideas even if it doesn't apply to my application.

Steve

He's been pretty absent over there now for a number of months. Deb scolded him, and he pretty much told them they could do without his input.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Steve, on my guitar in solera thread, it's not carbon fiber, it a laminate of spruce and ziricote. I'm trying to increase the mass a little in that brace. I've done some modeling with that design it seems to respond favorably to the extra mass there. I can't really comment on the outcome yet, but the box is closed up and it taps really nice, perhaps it'll make a nice drum if nothing else! But I'm hopeful.

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Jim Watts
http://jameswattsguitars.com

If you bond CF to the 'bottom' of the UTB in a horizontal plane, the brace is strengthened by CF's incredible resistance to tension. Bond it to the 'top' and the brace and it will benefit from CF's resistance to compression. Bonding it between two bits of spruce in a vertical or horizontal plane won't achieve very much at all because as Todd suggest, the centre of the beam is the neutral axis, i.e. tension and compression under load are at their lowest here so the CF is excused from duty.

Cheers

Kim

When I use CF to strengthen the upper transverse brace I do it like this. Which is what Kims referring to.

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Jim Watts
http://jameswattsguitars.com

Me too.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Me three.

Although I now don't scallop the ends of the UTB.

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Bob Connor
Geelong, Australia

Mario does use it mostly because of the set or the ability of CF to retain its shape and uses it on the X braces around .022" . Over that say .030" will make the the brace too stiff. He said at first he used it on finger braces but found it to be unnecessary and does not use it anymore in them. I don't think he uses it in the UTB.
I wonder if it doesn't then have a type of spring energy stored in it under the string tension that might have some effect on the top vibrating and the such?

I would not use CF anywhere in the bracing other than the UTB. Tonally I simply don't see the advantage and the structural benefits are not required elsewhere in the guitar and IMO only add yet another ball to be juggled in the quest for a good sounding instrument.

Cheers

Kim

Well, that could be said about a lot of things in guitar building, don't you think?

How thick is the carbon fiber you guys are laminating to your UTB's?

See, that's why it's important to have different forums with different MOs. That way you can get to experience both the users AND the admins chasing off pros!

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Well put Bob!

(Although I believe Mario was chased from here by the admins too... )

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

I don't think Mario was chased away from here, rather he kept getting people complaining of his direct nature. He didn't coddle, or beat around the bush, he was direct and to the point. While we all might not agree with everything he put out there I enjoyed his approach and having him around. I think the same thing happened with Rick Turner. Unfortunate on both accounts by my estimation.

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John Mayes
http://www.mayesluthier.com

I did this on my latest guitar.

This is totally unscientific, and Ive got zero measurements and such, but.... If I take my normal transverse brace like I've used for years ( .325 wide x .55 tall firmly butted up against my neck paddle which is also .55 thick) and hold it in my hands and try to flex it across the .55 height I can deflect it a little bit, if I push very hard, not as hard as I can, but I'm pushing quite hard. After I made this brace, which if it had no CF it would have been pretty weak, I took it and went to deflect it with similar force. Nada. No movement. So I tried to deflect it using every bit of force I could muster. Still did not budge. So while my method of testing was very crude I do believe this is much stronger than a same sized brace in solid Adirondack spruce.



EDIT: I got the idea for this from Howard Klepper, via John Osthoff.

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John Mayes
http://www.mayesluthier.com

Have not seen this before...!!! Thanks for the new idea. I would think a .02 or .03 thick strip on top of the UTB would be very sufficient. Looks like Mr. Mayes is doing something like that. I think Rick Turner does something similar with the back braces.
Tom

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A person who has never made a mistake has never made anything!!!

I use .03 also.

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Jim Watts
http://jameswattsguitars.com

Jim: Thanks for the thickness. Looks like lots of folks doing this. Guess I've been asleep at the switch. Thanks again.
Tom

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A person who has never made a mistake has never made anything!!!

This has probably been addressed in a BUNCH of threads, but what kind of glue are you using for CF to wood joints? I've been using HHG for CF, but I was able to break one joint in testing. I know polyurethane glue is super strong, but I'd have a hard time getting a joint as clean as I'm seeing in the pictures with PU glue.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Would not the UTB be alot stronger if the strip was laminated vertically? I can see where John is introducing an arch and that may be aiding some to strength.

Chris: Think I-Beam, the top takes the compression and the CF strip takes the tension.Not much chance of the CF strip stretching. Also a bit less material. Not sure which one would be the strongest.Engineer types will have to chime in here to let us know the answer.
Tom

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A person who has never made a mistake has never made anything!!!

Chris, I haven't ran the numbers but the CF mounted horizontally as shown in the pic should be much stiffer to the downward push of the fretboard ext.

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Formerly known as Adaboy.......

That just seems odd to me as if that was the case then why wouldn't one lay the CF in necks horizontal? I'm sure if you were to bend the CF before glued to the brace it would bend on the horizontal and not the vertical.
But then again I'm really not referring to John's if it's only .022"-.030" I can see how that would stiffen up the brace with the compression factor. But the others look like 1/8" thick.
Mario also once stated he laminated some thin CF to the bottom of a bridge or in a bridge and it was really stiff.

I'm not sure the way others do it so I can't comment on that. Mine is .020 and applied to the entire top surface. I didn't want to put it only on the middle section, leaving it off scoops, I wanted it across the entire surface, and curving it seemed it would not only allow that, but also make it stronger. It did both.

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John Mayes
http://www.mayesluthier.com

Absolutely the configuration as shown is the stiffest and strongest. In my banduras, there's a spot where I want a cross grain brace but there's some other stuff that gets in the way so I too laminate a short spruce brace with CF to get it as stiff as I can with so little room:



CF glued to the bottom of a truss rod channel would indeed be the stiffest, much stiffer than the vertical arrangement that's done now.

Something to consider though is that you don't always want or need the stiffest configuration. Mario sandwiches his CF in the braces which is the least effective use of CF for strength but, he likes that CF doesn't creep over time like wood does.

Same thing with the CF lining the truss rod channel - to fit it, you'd have to rout out the channel deeper which might not be possible and, what if the CF makes the neck so stiff that the rod has to fight to much for adjustment and it breaks?

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com