On Thursday, August 9, 2012 12:09:46 PM UTC-5, Clare wrote:
On Thu, 9 Aug 2012 12:58:59 -0400, "Existential Angst"

wrote:



"anorton" wrote in message

...



"Existential Angst" wrote in message

...

"stryped" wrote in message

...

I dabble in metalworking for fun. I also run marathons and some

triathlons. Been thinking it would be neat to be able to say I built a

bike and used it in the triathlon. I have a road bike but not a triathlon

bike.



As far as frame, I am limited becasue I dont have a tig welder. I do

however have a mig, oxy torch/weld set and arc welder.



I am guessing my choices are aluminum tubing or chrome moly steel.



I can mig weld the tubing with argon and aluminum wire but not sure if

this is ideal. I have read you can braze it.



I have read conflicting advice as to whehter it is recommended to mig

4130 or not. (The same for brazing it).



Weight is an issue. I want it to be light but at the same time be strong

enough to do a half or full ironman. 56 miles/112 miles.



I appreciate it!



sci.engr.joining.welding would be the better ng for this.



As far as projects go, my understanding is that unless you will be

hacking together black plumbing pipe and couplings, a bicycle frame is

probably one of THE most difficult welding projects to tackle -- a

deceptively difficult project all the way around, incl. fixturing.



The custom shop I visited used very high end dedicated tig, one brand

being Thermal Dynamics, and one other, something-arc (not lincoln or

miller). Fishmouthed thinwall tubing joints are not the easiest welds, a

lot of machine control is required. He showed me an innocuous small

bundle of tubing for his next build, a ridiculous price tag for a few

feet of tubing, iirc on the order of $500. Whatever it was made me gag.



Custom frames (the frame alone) start at $3K, and go up to $10K, mebbe

more. I assume there is good reason for this, but I'll spend only $19..99

on running shoes, so I'm not exactly on the same wavelength as this

crowd. I know they get the frame custom fitted for their body

dimensions, a big time consuming deal unto itself for pro's. I assume

there is a rec.cycling ng you could post to, to get some idea of their

bike requirements.

--

EA







It think if I were going to build a frame without proper tools and

fixturing, I would look at making a carbon fiber frame. Working with

carbon fiber is a lot like fiber glass. It is a lot of time and tedious

craftsmanship, but it seems very do-able at home. There are several people

on the web describing how they made theirs. Here is one:

http://theprojectjunkie.com/composit...e-project.html



Besides, your first homemade aluminum frame is probably going to look

second rate, but even a ratty-looking carbon fiber frame will be cool.



Indeed.

How much do you think carbon fiber tubing would cost for a bike? I imagine

the weight would come in around 5# or under.

Do it the old, well-proven way. Set up your frame in Chro-Mo tubing,

pinned together, then braze with oxy acet torch

Not sure what you mean by "pinned" togther but that is kind of the way I was leaning. (The cro mo).However, I have read you should not braze it. Something about the brass causing the wood like grain in cro mo tubing to crack.

I thought of carbon fiber hoever have no experience in it. I do not know how you would ensure it ould carry the reqhuired static and dynamic loads.

There are certain companies that offer "luggs". Basically you stick the round tubing into these pre made fittings to hold the material. It was the way bikes were made some time ago. Problem is a tri bike has a steeper seat post angle. (almost straight up). I have not seen pre made lugs that would allow you to do this.