General Cycling Discussion - properties of aluminum/ carbon fiber

I will attach a pic of the clamps for my fork. I think I can improve the top clamp.

My question is this: what are the differences in the different aluminum alloys? As in 6061 compared to 7075? Also, do any of you know of a good source for stock- I need a piece 1/2" think and 3" wide, 7" long.

Another ques- how about using a block of carbon fiber for this? I have some composite experience, and any weight I can knock off this thing would be good, I'm just not sure if it would be strong enough to be used as a clamp. Any thoughts appreciated.

Originally posted by MikeOK
I think I can improve the top clamp.


Whats wrong with it? They are pretty light already, I wouldent touch it. The numbers each mean something.....I think the last number or 2 tells the metal content or something.

I'm sure they made that clamp to fit any size (length) head tube. My Bullit head tube is very short, so the offset on the top clamp causes the clamps to end up too close to each other, even after I added all the spacers underneath it. In my case, I would be better off with a flat top clamp instead of the offset that is stock. I really don't like their pinch bolt design, seems it could be better. Plus, by increasing the distance between the clamps I will make the fork more rigid. It's very rigid now, don't get me wrong, but I still think I can make it better. I am using the stock stem that comes with it too, it's very cool. But I think I can improve that too with my own clamp by giving it more adjustability. Plus it's winter and I've completed about every other possible project I can think of :)

From what I've found just from visiting a few metal supplier sites (as well as my experience working with aluminum, as well as my degree in mechanical engineering..), I can tell you that 6061 is easier to work with, and is widely available for use as bracing, bracketing, etc. It comes in a wide variety of plates, bars , ingots, etc. Any machine shop or fabrication shop will have tons of 6061 laying around, since it is probably the easiest metal to work with. 7075, however, is not as widely available. It seems to be better for tubing, but is rarely seen as stock. Chances are, it has greater strenght/weight ratio, but is either more brittle, or has a lower cycles/failure ratio, or maybe it's just too expensive.
Carbon Fibre, OTOH, is notoriously poor in shear strength. The strength in CF is mostly along the lines of the fibres within the matrix. For this reason, I'd bet that a simple block of CF would be a poor idea for just such a project. CF is unidirectional in strength most of the time. Used properly, it can give incredible strenght for very little weight. Used improperly, it will break very easily. I can't see how CF could possibly be any use as a clamp.

http://www.brucescycleworks.com/tips/tip18.html
http://www.kleinjapan.com/tech_guide/2002_klein_tech_manual.pdf
http://www.worthsports.com/forming/materials.html
http://www.eastonbike.com/downloadable_files/r&d_files/R&D-01%20Al%20Alloys.pdf
http://www.alcotec.com/techpage.htm
http://www.bohemianbicycles.com/materials%20science.htm

D*Alex- I thought that might be the case with the CF. It would be more trouble to do it that way anyway, but the cool factor would be way up there. Also, there's a fab shop not far from my office, I bet they would have some 6061 laying around, I had forgotten about them until you mentioned that.

Hunter- thanks for the links, those were some good ones.

The Easton website gives a good explanation of the different properties of aluminium, also look for mil-hdbk-5. The only way to make a weight difference is to make the 7075 thinner than the 6061, being that the 7075 is stronger. But the only ways to figure out where you can thin the part is trial and error or stress analysis (know any engineering students?). Also the 7075 is much more prone to corrosion. 6061 is easier to get, machine and will not corrode. Make sure you get 6061-T6 not 6061-0. The -0 is very soft.

Boba- I noticed that on Hunter's first link above. There is a huge difference in tensile strength between the 6061-T6 and the -0. I was browsing a mag today and looking at the different alloys used in different parts. Seems frames are usually built with 6061 (they usually don't specify the -?), and things like chain rings are 7075 (and the -T6 is usually there). I guess the harder alloys are better for durability, and the softer are used for things like frames for flex. Interesting...

My frame is 7075.I asked the difference and they said its better because its lighter,stronger and rides better.So far the ride is fine.I can only compare it to my cannondale that had a front shock i locked out and my new bike is a lot better ride ever with 23c tires vs the 28c on the cannondale.Oh the cannondale is for sale,a very nice hybrid.

Actually, the T6 means that the metal is tempered. Heating the metal to a certain temperature, then cooling it at a certain rate will change the properties of the metal. Usually, though, as hardness and strength increase, ductility decreases, and the metal becomes more brittle and more corrosion-prone. Stress hardening does the same.