how much does carbon tubing cost?....and steel bottom bracket cages etc...

[bike_the_planet]

Ok....somebody stop me before I go mad with this...
But is carbon tubing expensive?
And are all the metal parts such as dropouts, BB cage etc possible to get/cheap?

Will I die if I do this?

I ask because I saw this: http://www.cyclechat.co.uk/forums/showthread.php?t=27899

Carbon fibre does not come in standard tubes. This is because carbon fibre does not have isotropic strength - ie it is not strong in all directions in the way that steel, al and ti alloys are. When you build using carbon fibre you have to build it as a complete structure and not as individual tubes joined together as with steel etc.

This is why many carbon frames almost look moulded in a fluid sort of way rather than tubes joined together.

Most people assume that carbon fibre is 'stronger than steel'. Well it is in tension (hence the claim that carbon's ultimate tensile strength is better than steels). But in compression it is weak. It's impact strength is relatively poor. This is why you have to carfeully consider the type of stresses that are present in a bike frame and build the frame accordingly.

That's why many modern carbon fibre bikes are built as monocoque structure.

Carbon fibre's other achilles heel is it's failure mode. Most metals have a failure point well above the yield point (the point at which the material deforms). Steel's a classic example - stress it too much and the early warning sign is that it will bend - permanently. But you have to stress it alot further before it will snap. Carbon doesn't do that - overstress it too much and it just gives.

If you want a carbon fibre bike - just buy one...

Tony

 

[youngoldbloke]

Carbon fibre may not be available in 'standard' tubes, but it is available in tubular form - see link to Carbonology earlier. Columbus (for example) also supply carbon frame tubes - see http://www.framebuilding.com/acrobat files/Columbuscarbonframesandtubes2009.pdf
Many frames are made as monocoque structures (at least, the main frame triangle, to which the rear triangle is then added), but earlier frames were made using a tube and lug approach. There is also an interesting 'how I made my own' how to do it article on the Sheldon Brown website. There are many examples of 'tubes joined together' - the carbon steerer tube attached to the forks, and the carbon rear triangles added to many top end aluminium frames are 'glued on' assemblies.

 

[Joe24]

I'm thinking of possibly (looong project) making a carbon fibre frame myself....but interested to see if this is just completely stupid or an actual acheivable, cost efficient idea.

Might not be so cost effective, and not something thats easy to do. You first have to get used to working with carbon fibre and doing the other stuff.
Im tempted to give one a go with making one up. Id have a nice tight fixed frame.
Something to look into i guess. I would be too worried with it snapping though i think

 

[bike_the_planet]

Carbon fibre may not be available in 'standard' tubes, but it is available in tubular form - see link to Carbonology earlier. Columbus (for example) also supply carbon frame tubes - see http://www.framebuilding.com/acrobat files/Columbuscarbonframesandtubes2009.pdf
Many frames are made as monocoque structures (at least, the main frame triangle, to which the rear triangle is then added), but earlier frames were made using a tube and lug approach. There is also an interesting 'how I made my own' how to do it article on the Sheldon Brown website. There are many examples of 'tubes joined together' - the carbon steerer tube attached to the forks, and the carbon rear triangles added to many top end aluminium frames are 'glued on' assemblies.

Carbon fibre is available in all kind of shapes.

However, when building with steel, ti and aluminium, because of isotropic strength af these materials, and the predictability of good welding, it is indeed possible to build a good reliable frame.

But with carbon fibre you have many more variables. How many layers of carbon? What direction to get the best strength to cope with forseeable stresses? What epoxy is used in the tube construction itself? What bonding agent will you be using? How long will the cure be? What tube and joint thickness?

The point is this: when you are flying down hill on your newly built bike and you hit a bump/ small pothole, how confident will you be that your frame will be stable enough not to get a bad case of instability or speed wobble, or worse still, fall apart?

If you are reasonably confident then by all means, build your own carbon frame. But you better be sure you get these variables right.

And I also caution against buying second-hand carbon frames and doing them up. You simply don't know what the previous rider might have done with the bike, eg involved in a collision. It is notoriously difficult to detect small cracks resulting from compression/impact stresses in the epoxy that could spell an early, and rather sudden, demise in the frame itself.

Cheers,

 

[montage]

Cheers Bike the planet - I don't think it is worth the risk to be honest .... I seem to be crashing far too much at the moment as it is