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CarbonFiber/WRC lattice bracing
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=36265		 Page 1 of 1
Author:  ernie [ Sun Apr 22, 2012 4:08 pm ]
Post subject:  CarbonFiber/WRC lattice bracing
I thinned a WRC top yesterday to abt 1.7mm and was planning to use it to build my first carbon fiber/lattice bracing for a WRC classical guitar. In the gore /gilet book Trev uses carbonfiber/balsa for the lattice bracing.In doing a bit of research I found that balsa wood varies in density tremendously from abt .08 to .40 .I have lots of vy light 1/4 sawn chocolate brn WRC. Has anyone substituted WRC for the balsa wood? and if so what were the results. In the sample photo in the book trev uses balsa wood with carbon fiber for the lattice bracing on a CL spruce gtr.
Author:  Trevor Gore [ Sun Apr 22, 2012 5:48 pm ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
Check out p4-42 (Design) bottom left frame, which shows a combination WRC/balsa lattice. Even good balsa is pretty close to its shear stress limit in this application (as noted in the text), which is why the WRC/balsa version came about.
Author:  Jim Watts [ Sun Apr 22, 2012 8:38 pm ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
Well, from an engineering point of view the correct orientation for a balsa cored panel, which is in essence what you're making, would be to use the balsa in the end grain orientation and you'll have plenty of shear strength then. This is standard for balsa cored panel construction.
Author:  Trevor Gore [ Sun Apr 22, 2012 10:14 pm ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
Jim Watts wrote:
Well, from an engineering point of view the correct orientation for a balsa cored panel, which is in essence what you're making, would be to use the balsa in the end grain orientation and you'll have plenty of shear strength then. This is standard for balsa cored panel construction.

Yes, that's correct, but there's a difference between "cored" braces and cored panels. The problem is not having the epoxy absorb into the end grain of an end-grain oriented brace so that the increased mass defeats the objective of the balsa. This is easier to manage on larger (and likely thicker) panels and is also probably why end-grain balsa didn't catch on as a core material (instead of Nomex) for double tops. As you can imagine, it's all a very delicate balance, never mind the challenge of constructing a classical lattice in end grain orientation.
Author:  Jim Watts [ Sun Apr 22, 2012 11:30 pm ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
Just trying to point out that balsa has terrible shear strength and when it is used in an engineering application, it's used end grain.
So, I'll just say it, the lack of shear stength would stop me form using it as a bracing material, I know others have used it successesfully.
I would imagine that WRC would be much better in that regard.
Author:  Jim Watts [ Sun Apr 22, 2012 11:40 pm ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
BTW: here's some cored braces out of Nomex. This was my very first guitar I guilt a little more than 15 years ago!
Don't do this, it's light, but its way too stiff and not really adjustable, but it was innovative in a bad kind of way. It's not that bad really, just difficult and didn't brimg anything to the table so to speak.
Attachment:
1st-top.jpg
Author:  ernie [ Mon Apr 23, 2012 6:52 am ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
Thanks trev and jim ,I/m a novice at this Will check p. 42 , but will probably use WRC , got lots of it. Although balsa is available at our local hobby lobby.
Author:  schrammguitars [ Mon Jun 18, 2012 8:57 pm ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
Ernie, check the density of your balsa. One block of balsa can have several wide range of densities. Generally I find that I can only use 10% -30% of each block. When I order medium density balsa many times I'll get a mixture of extra light, light, medium, heavy, and extra heavy density in one 3" x 1/2" x 48" board. I cut out the individual braces and weight them. The next consecutive brace could easily be quite different in density. Balsa is not very consistent. Here is some testing I did about 3 years ago:http://schrammguitars.com/balsa.html

Don't use balsa that you can easily squish with your fingers. Usually extra light and light density balsa and some medium density. WRC is usually equal to heavy and extra heavy density balsa. Very hard to find WRC that is lighter that 16 lbs/cu.ft.
Author:  Eric Reid [ Tue Jun 19, 2012 12:06 am ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
Jim Watts wrote:
BTW: here's some cored braces out of Nomex. This was my very first guitar I guilt a little more than 15 years ago!
Don't do this, it's light, but its way too stiff and not really adjustable, but it was innovative in a bad kind of way. It's not that bad really, just difficult and didn't brimg anything to the table so to speak.
Attachment:
1st-top.jpg


Jim--why are you dismissing this concept? Too stiff? Easy enough to change that. Not adjustable? Why not cap the Nomex with spruce? I would think that the idea you've got here would be at least as good as the carbon fiber laminate bracing that's being used by several builders.

Another question: Why do guitar builders stick to Nomex honeycomb? Wouldn't Kevlar be an improvement? What about PBO?
Author:  ernie [ Tue Jun 19, 2012 9:34 am ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
David thanks for the heads up abt the balsa. After reading abt all the densities of balsa on website vendors (didn/t know ) I went to several hobby shops.I found the density I wanted at michaels they had loads of balsa sheets in different sizes widths etc. I found a piece I liked after 1/2 hr of fiddling an testing.The balsa at lobby hobby was in plastic packages.
Author:  CharlieT [ Tue Jun 19, 2012 10:57 am ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
Jim Watts wrote:
BTW: here's some cored braces out of Nomex. This was my very first guitar I guilt a little more than 15 years ago!
Don't do this, it's light, but its way too stiff and not really adjustable, but it was innovative in a bad kind of way. It's not that bad really, just difficult and didn't brimg anything to the table so to speak.
Attachment:
1st-top.jpg


Jim - that's a pretty cool first guitar! I'm intrigued with the concept, even though it was too stiff.
Author:  Jim Watts [ Wed Jun 20, 2012 12:14 am ]
Post subject:  Re: CarbonFiber/WRC lattice bracing
Eric Reid wrote:
Jim Watts wrote:
BTW: here's some cored braces out of Nomex. This was my very first guitar I guilt a little more than 15 years ago!
Don't do this, it's light, but its way too stiff and not really adjustable, but it was innovative in a bad kind of way. It's not that bad really, just difficult and didn't brimg anything to the table so to speak.
Attachment:
1st-top.jpg


Jim--why are you dismissing this concept? Too stiff? Easy enough to change that. Not adjustable? Why not cap the Nomex with spruce? I would think that the idea you've got here would be at least as good as the carbon fiber laminate bracing that's being used by several builders.

Another question: Why do guitar builders stick to Nomex honeycomb? Wouldn't Kevlar be an improvement? What about PBO?


Eric, I basically think it's way to stiff which is easily remedied as you suggest, and using spruce would certianly help in that regard. Also there's really not much of a weight savings, braces just don't way that much, but I'm sure I could get it to work, but I'm not sure what it really brings to the table so to speak other than different. I've thought about other iterations of this in the past, but haven't really persued it, maybe someday.
As to the Nomex core I think it's used primarily because it's readily available in cell sizes and densities that make sense for guitar makers, that and we're a bunch of lemmings :). I think any of the engineering fibers could work as a core material for guitar applications if you have access to the core, but you probably wont have the selection of cell sizes and densities available to you that you have in a nomex core.
Thanks for the encouragement.
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