When we last left off, we had just got the seat tube to the point of being ready to weld the insert in place. I layed down a fusion pass that draws a bit of material from both pieces to join them together, then a second filler pass that was a bit heavier in the center rather than feathering in the edge. I set it up like this so that I can then skim pass the positive overage leaving a seamless, visually pleasing seat tube. Here we are with two seat tubes all ready for the next step; the binder bolt.
1.) keep the ovalized sections in phase, 90 degrees to each other
2.) swage the ti material to the approriate final size (remember the dreaded springback) without creating a peak or a subsequent crack.
3.) get through the now almost 2.5" inch long sections of thin tubing without destroying the tube...yikes!
The downtube took almost 4.5 hours, without taking time for pics. Why so long? Well, the swaging is not difficult, but does take time to do it right the first time. To achieve the final width I needed over the 12" tube length, the end of the tube almost closed off under the squeeze pressure. With the tube bi-axially ovalized, I then had to address how to miter it. Unlike Aluminum or steel, Ti will tend to pull and tear rather than cut smoothly, often dragging the side wall of the tube in with the direction of the cutter. To prevent this, I broke out the jigsaw and the sander and created internal wood plugs that matched the internal shape of the tube. This wooden plug allows me to miter the tube end in a supported fashion. It takes more time, but it saves some serious cursing and frustration if the tube gets destroyed by a wandering hole saw tooth.
A nice looong oval to round profile...