stryped wrote:
On Thursday, August 9, 2012 2:34:58 PM UTC-5, David Billington wrote:

stryped wrote:


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



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"Existential Angst" wrote in message



...



"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.



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.




Tell that problem with brazing to the big Italian tube maker, Columbus,

that tube is Cr Mo. The classic Reynolds 531, 753 and maybe a few of

their other tube sets were Mn Mo. IIRC the classic Italian bike were

often set-up on a jig and the joints drilled and pinned then removed

from the jig for final brazing. The last stage was then cold setting the

frame to make sure it was straight as intended. A number of other makers

did all the brazing in the jig to help keep the frame straight or

straighter.


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.



Make your own lugs. They came as sheet steel formings or investment cast

but I suspect you could fabricate your own. The other option is fillet

brazing.



One of the benefits of buying a standard tube set is that the tubes are

butted so thicker at the ends where required and thinner in the middle,

at least for some tubes, IIRC the seat tube is only thicker at the

bottom end where it fits the bottom bracket shell. The butting will be

one of the reasons a bike tube set is more expensive than just buying

standard Cr Mo tubing.


How would I go about making my own lugs without a mill????

Possibly with difficulty. The local frame maker near me uses or used to
use a Myford for the mitering of the frame tubes, lugs were bought in.
With the various jigs and other bits you're likely to need I think a
lathe and mill would be a worthwhile additional to the tool set. If you
can fashion wax masters and can get them investment cast in steel then
that would be a tried and tested method if not cheap. Hard silver
soldering requires tight fits, IIRC around 0.002"gap is optimum, brazing
is more tolerant of fit. Whatever you do it would be good to be able to
ream or bore the lugs to get a good fit. Then of course you need to be
able to braze a lug properly, I heard of a few cases in the US in the
early 1980s of frame makers popping up and making frames that fell apart
in use as they couldn't braze a lugged joint and get proper penetration
of the braze filler through the lugged joint.

Regarding lathe and/or mill if you don't want to get them and learn to
use them then I suppose a vice, files, and lots of time would suffice or
have someone else do it.