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warren
human power expert

USA
6050 Posts

Posted - 02/17/2009 :  10:21:07  Show Profile  Visit warren's Homepage  Reply with Quote
Hi All,

I'm thinking about building a weight weenie SWB recumbent bike using CF tubing. To use the parts I have available, it will probably be 24" front wheel, and 700C rear wheel. I'd like to use some pre-made 2" CF tubing, but don't know how thick it has to be.

This place: http://www.macqc.com/items.php has 2" OD CF tubing, but it's only 0.062 thick. Is that anywhere near thick enough?

ID(in.) - 1.875 OD(in.) - 2
Wall(in.) - 0.062
Weight(lbs./ft) - 0.251
Length(in.) - 70
$192.50

Thanks,

-Warren.


Edited by - warren on 06/28/2010 09:46:04

warren
human power expert

USA
6050 Posts

Posted - 02/17/2009 :  10:49:41  Show Profile  Visit warren's Homepage  Reply with Quote
Ok, so I found this:

http://www.carbonfibertubeshop.com/tube%20properties.html

Which lists:
the tensile strength (how easy it is to tear it apart)
the tensile modulus (how easy it bends)

So, my interpretation is that for a given tube OD and thickness, a CF tube is about 2/3 as strong as steel, and about twice as stiff.

Now I know that a 2" OD x .035 wall steel tube is plenty strong for a monobeam 'bent, so because of that I'm thinking that the .062 CF tube should be plenty strong, especially if I reinforce the high stress areas.

Anybody have differing opinions? Bueller?
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alevand
human power expert

USA
2876 Posts

Posted - 02/17/2009 :  11:41:51  Show Profile  Visit alevand's Homepage  Reply with Quote
I differ.

Tensile modulus for carbon composite is listed as 20 Msi and tensile strength as 275 ksi. 4130 Steel is 30 Msi and yields at 60 ksi. Thus steel is 3/2 stiffer per volume, but bends at a lower stress. Thus a .062 wall composite tube would be 4/3 (1.3) times stiffer than a .035 wall steel tube.

C:
Tony Levand
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warren
human power expert

USA
6050 Posts

Posted - 02/17/2009 :  16:29:13  Show Profile  Visit warren's Homepage  Reply with Quote
Hi Tony,

So, your opinion is that this tubing should be strong enough?

-Warren.
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Jeff Wills
human power supergeek

USA
1270 Posts

Posted - 02/17/2009 :  21:38:03  Show Profile  Reply with Quote
I recall that Robert Johnson at Terracycle built a carbon fiber highracer using a portion of sailboard mast as the basis. I recall this because I was looking at the bike at the OHPV meeting tonight. I don't recall the tubing thickness, but an email might answer your question.

__________________
Jeff Wills
All my bikes:
http://home.comcast.net/~jeff_wills/Gallery/index.html
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Hadden
recumbent enthusiast

United Kingdom
208 Posts

Posted - 02/18/2009 :  01:34:30  Show Profile  Visit Hadden's Homepage  Reply with Quote
On my semi-faired recumbent the Black Panzer I used 7 layers of 300g Uni HM carbon for the front tube plus some local reinforcement. This comes out at 2.1mm/.083" wall thickness. This gave a very light stiff bike at 8.5 kg http://www.fatbirdscc.co.uk/album_file.php?user=Hadden&album_id=2&media_id=15

simon sanderson

Edited by - Hadden on 02/18/2009 02:49:24
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alevand
human power expert

USA
2876 Posts

Posted - 02/18/2009 :  06:53:27  Show Profile  Visit alevand's Homepage  Reply with Quote
Warren,

I have no experience building with composites. From what I understand the main failure modes are compression buckling of the fibers in the matrix, interlamiar separation and impact damage. The carbon fiber tube is strong enough to replace the steel tube in the macroscopic sense. Getting the forces into the carbon tube will require local reinforcement, as you know. A plastic polymer layer over the tube will protect it from impact. How durable it will be the question. For occasional racing and training rides I think it would be fine, but not for commuting. I would not use filament wound tubing, as the fiber orientation is wrong for this application.

C:
Tony Levand

Edited by - alevand on 02/18/2009 07:01:22
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Hadden
recumbent enthusiast

United Kingdom
208 Posts

Posted - 02/18/2009 :  09:51:54  Show Profile  Visit Hadden's Homepage  Reply with Quote
In most cases it will be the stiffness not the strength of the fibres that determins the wall thickness of the tube. The failure mode will normally be microcracking of the resin between the fibres. The fibre orientation of filament wound tubes can be varied over a large range to give the required properties. Tape wound and roll wound tubes tubes are good. Pulltruded tubes would be the ones to avoid as their fibres are only in the 0 degree axis. Tubes are quite easy to make using prepreg cloth or uni tape wound over an Ali tube that has been polished and coated with release agent. Then compressed with a plastic heat shrink tape and cured in a cardboard tube with a heat gun. http://www.flickr.com/photos/bhpclub/2457486714/in/set-72157604828238682/

simon sanderson

Edited by - Hadden on 02/18/2009 10:02:27
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calfeenated
recumbent enthusiast

USA
226 Posts

Posted - 02/18/2009 :  21:13:26  Show Profile  Reply with Quote
Warren,
IMHO, .062 is not thick enough by itself. If you notice on the macqc site they also make a tube that is almost a perfect match to go on the inside of the 2" as well. sort of like internally beefing up the tube. Perfect for re-enforcing the head tube area and the chain stay area.
Also, Notice that they make bicycle specific tubing as well that is slightly thicker and is specifically wound for resisting bending loads rather than torsion (twisting).
If you plan on hand wrapping carbon roving (Tow) around the joints then even better yet.
Let me know if you need roving, I have a few thousand feet of it...
Don't ask why...


Mark.
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Charlie Ollinger
recumbent enthusiast

USA
187 Posts

Posted - 02/18/2009 :  21:53:21  Show Profile  Reply with Quote
From my experience converting metal structure to composite, I'd say that tubing is too light. As is, using just that tubing, you would have about 60% weight savings over steel, and I'd bet a good design would be more like 40% savings.

Failure, as was already mentioned, will be in the resin, and we don't know how much strain the resin will tolerate. We also don't know the majority of fiber orientation. If its mostly wound at 45degrees or more (more axial), its probably okay for the boom. For the main tube, you would probably want to add some uni top and bottom, and then make sure you get good wraps to the headtube, and put a lot of thought into the attachment of the chainstays.

The trouble here is if you're too light, you don't know it until you've seriously damaged it.

Charlie
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warren
human power expert

USA
6050 Posts

Posted - 02/19/2009 :  09:34:22  Show Profile  Visit warren's Homepage  Reply with Quote
Thanks all!

Here is the current plan (subject to revision at whim).
* Mark has a tube, which is probably a bit light. I'll wrap the tube in one of the biaxial sleeves listed here to beef it up. http://www.sollerpaddles.com/composites/carbon%20fiber%20sleeves.html
* Joints wrapped with carbon roving
* Run cables inside frame
* Possibly fill main tube with expandable foam (thanks Garrie)
* 24" front wheel with CF aero fork (already have)
* CF rear chain stays (already have)
* XL CF VK seat (already have)

Now I just need to decide whether to build my own handlebars out of CF tubing or buy a premade item.

-Warren.
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Larry Lem
human power expert

South Sandwich Islands
2523 Posts

Posted - 02/19/2009 :  10:16:04  Show Profile  Reply with Quote
Does this mean there's nothing left to do on the Cuda-W?

Larry Lem
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warren
human power expert

USA
6050 Posts

Posted - 02/19/2009 :  11:22:35  Show Profile  Visit warren's Homepage  Reply with Quote
HaHaHaHaHaHa....

All I have plans for this year on the Cuda-W is to make it so I can turn the *&$*@&( front wheel a bit without the tire hitting things like chains, chainrings, and cranks. I have the chain and chainring thing under control now, and decided I needed to go to a 155mm crank to avoid that crank-to-tire problem. I ordered these cheap BulletProof cranks in 155 length. They arrived, and it looks like they used 165 or 175 cranks, and just drilled the hole at the 155mm location. @$&*! So now I need to get out the grinder and attack the brand new cranks to make them work.

If I have 3 projects to work on at once, then there is almost always something I can do on one of them while the other is waiting for:

a) parts
b) patience
c) epiphanies
d) weather conducive to doing stinky stuff outside

-Warren.

Edited by - warren on 02/19/2009 11:25:22
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alevand
human power expert

USA
2876 Posts

Posted - 02/19/2009 :  14:06:10  Show Profile  Visit alevand's Homepage  Reply with Quote
Why is 45101 only $15 ? (maybe they are tent poles)

The 45309 2.4-50-FABR, 2.54 OD fabric outer layer is probably stronger than 45536 1.875-70-11P 2 in OD uniaxial outer layer. Torsional stiffness goes by diameter to the 4th power, thus 2.54 OD tubing is 2.6 times stiffer in torsion and bending than 2 inch tubing and 2 times stronger in both bending and torsion.





C:
Tony Levand

Edited by - alevand on 02/19/2009 18:52:15
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Hadden
recumbent enthusiast

United Kingdom
208 Posts

Posted - 02/20/2009 :  11:29:25  Show Profile  Visit Hadden's Homepage  Reply with Quote
This is only true for bending if the walls are thick enough that the cross section does not deform under load. (One of Eulers formula)

simon sanderson

Edited by - Hadden on 02/20/2009 11:53:30
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alevand
human power expert

USA
2876 Posts

Posted - 02/20/2009 :  11:33:28  Show Profile  Visit alevand's Homepage  Reply with Quote
Yes, in either case the wall is 1/16 inch thick and both would be "shear resistant".

C:
Tony Levand
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warren
human power expert

USA
6050 Posts

Posted - 05/01/2009 :  16:47:29  Show Profile  Visit warren's Homepage  Reply with Quote
The parts are starting to come together for a weight weenie CF bike. I have collected weight weenie parts that didn't seem to fit with any other project:


And I decided to buy a CF tube from Mark Anderson. The CF tube is a little light duty, so I'm going to cover it in a Soller composites sleeve.

More here:
http://www.recumbents.com/wisil/stickbike/

-Warren.


Edited by - warren on 05/01/2009 17:29:04
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JS Tyro
Starting Member

Canada
2 Posts

Posted - 05/17/2009 :  21:52:28  Show Profile  Reply with Quote
I may be late to this party, but maybe you want this: http://www.sciencedaily.com/videos/2008/1201-hitech_cycling.htm

Edited by - JS Tyro on 05/17/2009 21:52:52
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warren
human power expert

USA
6050 Posts

Posted - 09/14/2009 :  10:07:15  Show Profile  Visit warren's Homepage  Reply with Quote
I am now beginning work on the CF stick bike.

Mark A. had sent me some super-lightweight two-part filler putty, which I used to join the main tube to the rear stays. It's cool stuff. It starts out kind of powdery but ends up doughy after kneading it for a while.



I notched the CF tube, and put the tube and the CF rear stays in the frame jig. The rear stays have a replaceable derailleur hanger that I did not get with the fork, so I had to laborious hand cut and file an old hanger that I had in my scrap bin. Scrap bin to the rescue again!



Next weekend I'll trim the leading edge of the seat stays until they look right, and then start covering the mess with CF.

http://www.recumbents.com/wisil/stickbike/default.htm

-Warren.

Edited by - warren on 09/14/2009 10:07:55
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warren
human power expert

USA
6050 Posts

Posted - 11/12/2009 :  18:45:58  Show Profile  Visit warren's Homepage  Reply with Quote
Has anyone seen these CF tubes up close?

http://www.cabelas.com/p-0065089321015a.shtml

Good price, Would they work as seat stays?

-Warren.
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Kragasaur
recumbent enthusiast

259 Posts

Posted - 11/13/2009 :  19:04:42  Show Profile  Reply with Quote
Warren,
Did you see any indication of their diameter?
Eric
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calfeenated
recumbent enthusiast

USA
226 Posts

Posted - 11/13/2009 :  23:12:33  Show Profile  Reply with Quote
Warren,
It's tempting but I wouldn't go there...
You have no idea how they are woven and if they were meant to do what you'r trying for.
If you are looking for seat stay material I have some great maclean tubes ranging from 1/2 to 3/4 inch in diameter and meant to take axial loads and some bending and of course, very light.
contact me off list.



Mark.
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Speedbiker
human power expert

USA
3704 Posts

Posted - 11/14/2009 :  06:25:35  Show Profile  Reply with Quote
Hey Warren,
Where did you get those nice, premade
stays? Is this bike going to position
your body in a competitive manner? It
looks promising. One day I'll have a bike
that is as light as it is aerodynamic :~)

Thom
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warren
human power expert

USA
6050 Posts

Posted - 11/14/2009 :  07:21:10  Show Profile  Visit warren's Homepage  Reply with Quote
Hi Thom,

Don Smith had several sets of these, and I bought one several years ago. I'm not sure if he has any left.

I am going to make this bike have the same riding position as the NoCom, so the riding position should be good. I may have to cut the main tube and give it a slight bend at the head tube to make the BB lower as the NoCom has a 9" seat to BB height differential. The only thing I am apprehensive about is the long tiller that will be required. I really don't like the superman bars.

-Warren.
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warren
human power expert

USA
6050 Posts

Posted - 11/14/2009 :  07:23:57  Show Profile  Visit warren's Homepage  Reply with Quote
There was no info on the Cabelas CF tube other than length. I have looked at a bunch of other CF tubing online and was scared by the prices. I did see a couple tubes on EBay for reasonable prices, but not in the sizes I wanted.

-Warren.
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raymondg
recumbent guru

865 Posts

Posted - 11/14/2009 :  09:31:16  Show Profile  Reply with Quote
Warren,
There's plenty of sources for tubes on the internet that have better info, so not sure why you would want to go with such an unknown.

Of course...you can easily wrap your own. I've made quite a number of tubes over the years by wrapping over aluminum tubing mandrels. Wrap CF cloth over the polished and mold released aluminum, use heat shrink tubing over everything for compaction/surface finish, cure at elevated temp (like from blowing a space heater into an insulated box) and shock cool after cure with ice water through the tube. Pull the CF tube off the mandrel quickly while the aluminum is still cold....and voila! nice new carbon tube. You can make any layup you want that way, including local uni or bid reinforcement as needed.

Raymond
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