On Jun 7, 1:49*pm, cavelamb wrote:
Michael Horowitz wrote:
I'm practicing making joints.

I built a simple jig to hold *two pieces of tubing parallel and about
6" apart and have notched and placed a third piece of tubing,
connecting the two parallel pieces at 60*

To minimize warpage from the heat (I'm using gas) I know I should tack
one side of the joint, then the other, then repeat at 90*

So how do I get to the other side of the joint (for the second tack)
if it's lying flat against the board? Certainly the folks building a
fuselage don't take it out of the jig after doing only one of the four
tacks per joint - Mike

The way I did mine was to tack front and back sides while in the jig.
Tack left and right after it's out.

Heating metal to cherry red tends to shrink it. I will measure parts
as each tack is cooled to see where it needs to be shrunk to walk it
back into alignment and add the next tack there. I continue this
process as the welds are completed. With experience, a welder can
produce tubular parts within a few thousandths of spec.

Gas welding tends to heat a larger area than say TIG so parts can
suffer greater warpage. However, I've carefully reheated TIG welded
tubular structures with a gas flame to remove warps.

I love gas welding but if I were to do another welded fuselage, I'd
bite the bullet and buy a TIG welder. It's much faster and cleaner.