Originally Posted by CATZ
On the bent, I'm building, I'm MIG welding.
The problem with this is, as you go around the tube, you have to stop and reposition. This leaves a hump, where you restart. TIG doesn't do this because you can remelt for the restart, without adding filler. .. or in the case of the robot welded joints, there is only one start.
The excess filler can be removed with die grinder, file or whatever, but this leaves an area to be "finished". ... On the bike stand I made, I went through this process, but additionally applied braze, after grinding and filing, to form a more even fillet and to fill some of the irregularities. This evens out the whole joint, creates a nicer fillet, and leaves a softer metal to finish.
It may not be "politically correct", but I think it will come out good, ... and strong. ??
I don't know about politics, but it sounds like you are subjecting those tube to a lot of heat cycles. You do not say what kind of material you are using; since you are MIG-ing I assume it is steel. Every time you heat the tubes (and allow them to cool) you are altering (& degrading) the structural properties. Steel (& aluminum, for that matter) can get brittle or crystalized after too much of this, which can cause tube failure, usually right at the edge of the weld.
I seem to remember Cannondale saying they heat-treated the entire frame after assembly to compensate for this, but I'm talking maybe 10 years ago so I could be mistaken.
MIG is best for automated set-ups because it's fast & strong; one pass and the robot's done.
If you know how to braze why not just build that way and skip the welding?