Is this carbon fiber unusually flexible? Low grade?

Ask your wood and other materials questions here. Please DO NOT post pictures and ask us to identify your wood, we have found that accurate ID is nearly impossible, and such discussions will be deleted. Thanks.
Post Reply
Liam McGillivray
Posts: 18
Joined: Thu Dec 21, 2017 3:07 am
Location: Vancouver, BC, Canada

Is this carbon fiber unusually flexible? Low grade?

Post by Liam McGillivray »

I bought these carbon fiber rods from Aloft Hobbies. They are 1mm×6mm×1m. While I realize that 1mm is quite thin, and that they resist flexing better in the 6mm dimension, they are still less stiff than I expected. Here is a video of me wobbling it in the 1mm dimension. However, I am able to slightly bend it in the 6mm dimension by hand, although that's harder to demonstrate on video.
https://youtu.be/7Yh0zUhM8Ow
I bought them to run through the neck and body of my instrument, as I want very high stiffness for piano-like tone. I was planning to glue multiple of these together so that they're 2×6mm, or 3×6mm.

When I was shopping online for carbon fiber, I decided that I needed a length of 92-100cm (or 36"-40"), preferably in the upper end of that range. Before I considered this 0.236"² and this 0.125"×0.325" rod from Rock West Composites (cut into appropriate lengths by their service), and also this 0.187"×0.325" from DragonPlate. But those are more expensive. DragonPlate may appear cheaper than Rock West Composites, but they require a shipping quote by e-mail, which ended-up being $46 for me on-top of the $30 minimum order.

I chose Aloft Hobbies instead because it's much cheaper. But they are not nearly as stiff as I expected. I read here that stiffer grades of carbon fiber have a higher "msi". I shouldn't be surprised if Aloft Hobbies are a lower grade, given the lower price, but I don't want to choose the more expensive option if they don't provide specifications to prove that they are high-grade.

Do you think this carbon fiber really is too floppy for it's size, or is this just usual for carbon fiber if this size?
Liam McGillivray
Posts: 18
Joined: Thu Dec 21, 2017 3:07 am
Location: Vancouver, BC, Canada

Re: Is this carbon fiber unusually flexible? Low grade?

Post by Liam McGillivray »

Update: I found here that Rock West Composites standard modulus carbon fiber is 33 Msi, and that this is a measure of "tensile modulus". However, I don't know if Aloft Hobbies has the same or lower.

When I ordered from Aloft Hobbies, I felt like probably any carbon fiber would be good enough.
JC Whitney
Posts: 208
Joined: Mon Jan 09, 2012 1:19 am

Re: Is this carbon fiber unusually flexible? Low grade?

Post by JC Whitney »

A ratio of 6:1 depth to height makes it tough for a beam to resist Y axis bending, as it doesn’t have enough X axis material to resist buckling (I may have my axis swapped, but hopefully you get the idea). If you laminate several of those 1 mm strips together and can get closer to a 6:3 or 6:2 ratio I bet you’ll be surprised at how much stiffer the resulting member is.
Brian Evans
Posts: 922
Joined: Sat Aug 30, 2014 8:26 am
Location: Tatamagouche, Nova Scotia

Re: Is this carbon fiber unusually flexible? Low grade?

Post by Brian Evans »

If you constrain it in a slot so it cannot "wobble" you will gain all of the value of the 6mm stiffness, whatever that might be.
David King
Posts: 2690
Joined: Sat Jan 07, 2012 10:01 pm
Location: Portland, OR
Contact:

Re: Is this carbon fiber unusually flexible? Low grade?

Post by David King »

You'll get 4x the stiffness by going to a 12mm wide assuming you have the depth in the neck. I use 1/2" x 1/8" pultruded spars and embed 1/8" into the bottom of the fingerboard which makes a very stiff assembly. A couple of 1mm x 6mm profiles probably won't make any measurable difference in most necks. Call Allred and see if they have Canadian distributors, that should save you a bundle in shipping at least. Pultruded CF is a pretty ubiquitous product.
Ron Belanger
Posts: 153
Joined: Fri Jan 06, 2012 8:54 pm
Location: Orillia, Ontario, Canada
Contact:

Re: Is this carbon fiber unusually flexible? Low grade?

Post by Ron Belanger »

Josh House Canadian Lutherie Supply has 1/8 x 3/8 pultruded strips. I order mine directly from Allred (Dragon Plate). I usually order 6 or so 4 ft. lengths. Makes the shipping cost worthwhile.
Clay Schaeffer
Posts: 1674
Joined: Fri Jan 06, 2012 12:04 pm

Re: Is this carbon fiber unusually flexible? Low grade?

Post by Clay Schaeffer »

" I want very high stiffness for piano-like tone"

Why do you feel this will give you a piano like tone?
Post Reply

Return to “Wood and Materials Q&A”