I'm practicing with an Ox/Ac rig; Using mild steel (.035).
Got a little cocky and decided to try a patch on tubing. With a
rosette weld as well as along the edges.

Well, I chased that hole all over the patch! burning it and filling
and burning and filling! The patch obviously getting hotter than the
base metal. Tried different angles, nothing successful. Any
suggestions are appreciated.

Had the same problem along the first edge. Then I wised up and clamped
a 'chill bar' on the patch. Worked like a charm; however, I can't see
an experienced welder stopping for each side and reclamping the 'bar.

I'm using 2psi of both gases, and a blowpipe tip with an opening
appropriate for metals .037 thick.

Suggestions? - Mike