On 8/9/2012 11:28 AM, anorton wrote:

"Existential Angst" wrote in message
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"anorton" wrote in message
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"Existential Angst" wrote in message
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"stryped" wrote in message
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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.
--
EA


I have never tried making anything myself in carbon fiber. It is used in
some lightweight, airborne assemblies I have designed optics for.
Here are some retail prices of pre-made tubes:
http://www.rockwestcomposites.com/br...n-frame-tubing


And raw cloth:
http://www.tapplastics.com/product/f...cialty_fabrics

It looks like you might spend $200 to $300 on frame materials and epoxy
plus the purchased metal components. Of course the real cost would be time.



carbon fiber tubes are commonly made in the sailing community. i have a
tiller that is made out of this, really strong and light.