Framebuilders - would this work?

sorry if this has been discussed before, i did a quick search (here and google) and did not find what i was looking for.

so i was thinking. if you had an old steel frame, could you cut out the tube parts and replace them with carbon fiber tubes? would this be safe? or even effective?

the parts boxed in red would be cut out and then replaced with CF tubes. (this is not my bike, photo borrowed from www.pelagodesign.com/blog/tag/commuting/)

http://images2c.snapfish.com/232323232%7Ffp53659%3Enu%3D338%3A%3E359%3E3%3A3%3EWSNRCG%3D324838%3C%3B%3C8343nu0mrj

um.... why?

in theory, you could debraze the lugs, find carbon with the same inner diameter, and glue them in place. or you could just cut up the frame, then find carbon tubes that fit inside or outside of the tubing "stubs" there.

I had a friend who wanted to do this to make a bamboo bike. then he started working on bikes, and couldn't bring himself to cut apart a bike that had a comfy geometry for him.

it COULD be done. but what would you be gaining? seems like a lot of cost and danger. if its for looks- you could just get some carbon fiber and wrap the frame in it. if its for weight savings, there are other cheap aluminum frames on the market.

my main intentions would be for weight reduction. though im not really sure it would take that much off. would it not also soften the ride a bit?

what do you mean by danger? the bike possibly falling apart while riding down a big hill or the danger of putting money into a project and ending up with a pile of chopped up bike parts taking up space on the garage floor. :lol:

im not sure i would actually do this (i have quite a few projects on the list already taking up time) i asked mostly just out of curiosity. (had it been done, would it be worth doing, any real benefits to make it worth the time and money...ect)

im planning on putting a single gear (maybe fixed) bike together and im just trying to think of ways to make it as light as possible. (and cheap) i found an old bike locally that someone is selling for only 45 bucks, i haven't seen the bike in person yet but from the pictures it looks like what i want to start with. the seller did not say what material the frame is made of but it looks old enough to be a steel bike

I saw a bike that followed a similar concept, except it was built that way originally. I forget the brand.

I wouldn't do this. There is a good reason why most composite frames have larger tubes.

I've owned several bikes with "standard diameter" carbon tube glued into lugs. They were all swingsets, and none were very light compared to today's bikes.

This is a very poor idea and I would forget it post haste.