RubeRad

First post on the framebuilding forum, I apologize if I'm asking some dumb question that comes up all the time (I searched a little bit).

I clicked on an ad presented to me here at BF, and got an idea...

I'm no metalworker. BUT, I think I could manage to take a middling old-school lugged steel frame, learn enough how to use a torch to get the main triangle out of the lugs, buy some round carbon tubing in the same diameter, cut the tubes to match the removed tubes, and epoxy that sucker back together.

Seems to me that's a pretty simple plan that will bypass a lot of my design and tool-owning shortcomings, and "create" a bike that is cool and unique.

Would that work?

Do carbon tubes need to be significantly bigger than 1" steel tubing to achieve the same strength?

Does super-pricey high-modulus carbon or specialty bicycle tubing need to be used (that would nix the deal right up front)), or would regular unidirectional be ok? (0, 45, 90?)

Would handling or other properties of the frame be affected (better? worse?)

Would I suffer catastrophic bicycle explosion on my first 45mph descent and die?

unterhausen

your idea comes up now and again. The issue with reusing lugs is that they don't have enough surface area. Tube to tube carbon construction is done with sheets of carbon fabric. Of course, the better the material properties, the better the bike will work. Your first bike will probably explode. I want to build a carbon bike, but it's on a long list of things to do

fietsbob

Bamboo tubes get a wrapping with Carbon cordage and epoxy, to join them ,
substitute a carbon composite tube for the bamboo?

hamster

It will not be the lightest carbon frame in the world. Supposedly, a good deal of thought goes into the specific design and fiber orientation in every part of the frame, to maximize stiffness and durability while minimizing weight. If you're doing a straightforward replacement of steel tubes with unidirectional carbon tubes, you'd have to play it safe with wall thicknesses.

An important property of the frame (especially of a carbon frame) is torsional stiffness. Imagine fixing the rear triangle vertically and trying to twist the frame by pushing the front fork sideways. High stiffness is desirable for handling. If you build a bike out of unidirectional carbon tubes, I think it's going to be extremely flexy. You need some 45 degree fibers in the top tube and the down tube.

Junctions between carbon and steel will be your weakest spots. Even carbon-to-carbon junctions (between layers of cured epoxy) are not as strong as one-piece carbon constructions. Bonding carbon tubes to steel lugs would probably be a pain to do in a safe and secure way. It may be best to use steel lugs as molds, assemble everything and wrap epoxy-saturated fabric around them.

If you want to pursue this, I have some composite fabrication supplies (a gallon of epoxy, mold release, etc.) laying around, I might be able to give a hand.

unterhausen

take your cues from a bamboo frame, only use carbon. There are construction sequences for carbon on the web. Lugs don't align anything, so you need a way to hold the tubes in place. I would leave them out due to the potential for corrosion

Best to use oversize tubes.

RubeRad

Oh wow, and you're right around the corner, so to speak (I live in Poway). Frankly, since the feedback is that my idea is not super-good, or at least it's only a beginning, and a lot more work would have to go into it, I'll probably never get around to it. However, if you are working on a frame some Saturday and wouldn't mind somebody looking over your shoulder, admiring your tools, and generally being pesky...

And damn, Elev. YTD: 188778ft? That's over 1000 ft average, every single day this year! Do you just ride up and down Palomar all the time?

Canaboo

You can just miter and tack and then make your own lug with a number of varieties of carbon cloth and/or tow.
While carbon is supposedly used in all sorts of specific orientations in order to achieve stiffness in one direction and flex in another you can likely achieve a "steel like" ride by just using a generic carbon tube that has a uniform mix of unidirectional and woven.
Look at a typical carbon seatpost. Tubes like that are available from Aircraft Spruce for example.

busdriversrock

I did something very close to what you did a few years ago. At the very least, I learned a ton about frame construction. Because I did not have a vacuum system, I was going to lay fibers on a foam core. So, I decided to research some foams that had actual construction properties, and I discovered a marine foam core called Core Cell. I purchase my carbon from a online tuner car shop (3k weave), along with kevlar, etc., and used the West System (super awsome) for Epoxy resins. I used an awsome glue made by Plexus designed for exactly the adherance of aluminum and epoxy (I did research on this too, and used the glue in metal fab construction). I purchased my stainless drops and aluminum headtube/BB/seattube from Nova, and I constructed my jig out of laminated wood (actually very accurate - I used my calipers for measuring), and purchasing some small vices for holding the bottom bracket, and constructing axle jigs, etc., I managed to produce something that looked like a frame, but really was super sub standard in strength. As soon as I rode it, I knew it was going to break, but I spent so much time building it, that I was going to ride it, damnit! And I did a faceplant about a block from where I live. I did work in a meta-fab shop, and the next frames I make will all be metal. This bike probably cost me 1k to 1500 to build. Like I said, I learned a lot!, but I don't have any plans to attempt it again. I have seen many people attempt it, and some constructions are absolutely fantastic, but they are pros, not hobbiests like me, who are looking for something to do. They cut their teeth in the industry already - kinda why I'm going to concentrate on metal, if I ever get around to it. If I were you (and I have thought about doing this), is start by getting damaged carbon frames off of eBay, and start repairing them. You will learn alot just from this, and at least you may have something to ride once you are done.

hamster

I don't really work on frames, I just saw this post by accident, and I have the stuff left over from the time I was experimenting with it last year. I like the general idea of making my own carbon frame, but I have a feeling that it's going to be a huge time sink and I can think of 20 other things I'd want to finish before I start this. Starting with preformed tubes would simplify things a bit.

As to the elevation - Escondido (at least these parts) is a bit similar to Poway, except that it's hillier. I live 20 min from the bottom of Bandy Canyon -> Highland Valley Road, 25 min from the bottom of Lake Wohlford Road, and it's less than 1:30 from here to the foot of Palomar. (Which I don't ride nearly as often as I should.) There are three general routes leading to & from my house, two out of three involve 400+ feet of elevation change in the first two miles.
Besides, I did a bunch of climbing centuries earlier this year (KOM series and MLBC).

MichaelW

Carbon in direct contact with metal can generate corrosion. Even with carbon tubes, you still need metal at the headset and bottom bracket. Almost all frames use an insulating interlayer of glass fibre. I have seen broken steel frames with a temporary fix of glass fibre wrap, some in use for many years.
You need to test your construction method to complete destruction. Maybe setup one carbon-wrapped joint and break it.
The rear triangle needs some curvature to avoid heel interference so many builder just buy a pre-made rear triangle, eg Deda.

seankanary

There is really good carbon building info in THIS thread.