Its neat to watch others weld on challenging projects. I've been welding since 94 and now run my own welding business. I concur on welding the perimeter complete first. I kind of think of it as conquering the conditions and injecting quality alloy to build off, once you got it ringed you know that it will cover. Sometimes back purging really helps especially if the cavity your tigging over reverberates with the frequency your using on a\c this reverberation being a sound wave causes the argon to bounce, drawing in raw atmosphere into that argon envelope and causing a scuzzy puddle. Back purge solves a lot of issues in challenging conditions with tig or at times even a piece of tape covering the base of the cylinder but not completely sealing it is all it takes to get a better puddle. Tin foil makes a good gas barrier sometimes I just pack the area behind the weld zone with a crumpled up tin foil ball . In the future you might try feeding the rod from inside the combustion chamber and torch from the outside for fun, a positionable vise would be key for this, I've done holes both ways and sometimes its easier, sometimes not. Fun stuff for sure. Nice job!
