On Thu, 9 Aug 2012 05:52:51 -0700 (PDT), stryped
wrote:

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!

Having built a few bikes I have a few comments.

All of the top triathlete people are riding carbon fiber bikes which
are notably lighter then metal bikes, which has an effect on climbing.
But that being said,

If you use aluminum you not only need to weld it (TIG or MIG) but you
need to heat treat it after it is welded. Columbus, for example,
states " The heat treatment is strictly recommended, 4/5 days after
welding: artificial ageing 6h at 90°C, then 4h at 150°C."

This presents a problem to most builders as it requires an oven large
enough to hold the entire frame.

Steel frames can be built by using lugs and silver brazing the joints
or by filet bronze brazing the joints or by TIG/MIG welding the
joints. The lugged frame will probably be a few ounces heavier then a
non lugged frame.

The question of 4130 really doesn't enter into the equation as if you
are planning a serious bike you will want to use butted tubes and so
will need to buy the tubes from companies that make special tubes for
bike frames and they will be weldable.

I suggest that you download Columbus' catalog
http://www.columbustubi.com/eng/1.htm
There are recommendations for welding/brazing each type of material.

Columbus also sells carbon fiber tubes and other bits. I'm not really
familiar with building carbon fiber frames but I assume that you cut
and fit the tubes and then wrap the joints with carbon cloth and epoxy
them.

Some added comments. A carbon fiber frame can be as light as 900 gms.
The lightest lugged frame I've built (52 cm top tube) is 1300 gms. for
the bare unpainted frame.

Depending your weight it would be difficult using normal bicycle
tubes to build a frame that would not be strong enough.

Frame alignment will be difficult to control without some form of jig
to hold things. There is some question as to just how accurately the
frame needs to be aligned but certainly there is some point where
misalignment will effect handling.

Tri bikes have different geometry then normal road bikes. Usually a
more upright seat post and shorter top tube as they are usually
designed to be used with aero bars. However, this will also move the
CG forward and I'm not sure how much this effects handling.

Download THE PATEREK MANUAL
(icelord.net/bike/paterek.pdf) and read it. It is the original
edition and there is a later version that Paterek sells but the older
(free) edition contains all the information you need.

That is all I can think of at the moment but if you want more
information just ask.
Cheers,
John B.