At 9/26/2006 01:24 AM +0100, Norris Lockley wrote:
>...just how amazingly skilful does a builder have to be to
>fusion-weld fine gauge tubes..possibly as fine as 0.9, to a thick bottom
>bracket shell without "holing" the finer pieces?
For joints like this, knowledge, practice joints and planning are as important as dexterity.
It's not much of a trick to fusion weld two 0.6mm tubes together, using 0.82mm ER-80S rod. And I've butt welded 0.25mm strap using a single strand of brake cable wire for filler rod. That was with a Smiths AW1 aircraft torch. Now that I have a couple of jeweler's torches, I wonder how thin I could go (if my hands and eyes were 30 years younger).
0.9mm to a BB would be tricky if the BB shell were very thick. I like to bore my shells out to save weight, which would also help in the cause. I imagine he preheated the shell quite a bit. Portholing would also make it easier, as would using a loose fitting aluminum plug in the thinner tube to limit the amount of oxygen getting to the back of the weld.
I use these plugs when TIG welding. A surprisingly effective poor
man's argon purge. Little or no scaling on the interior.
>Has anyone on the List come across similar types of construction on a
>quality frame..or have any of the List's frame-builders risked their
>reputations carrying out this type of construction?
I did oxy/acetylene fusion weld a recumbent frame once. But I think there would be too much distortion at the ST, TT, seatstay joint for a good seatpost fit. (I don't like to have to ream too much)
Mark Stonich;
Minneapolis Minnesota
http://mnhpva.org
http://bikesmithdesign.com