[sdubfid]

Just because a shop has a tig welder doesn't mean they can operate it properly. I have a knife but I wouldn't perform surgery.

I think godwin means ac for aluminum. DC can work but you would use AC 99% of the time at home.

My tig sells for $4000 and I have used $500 tig welders that will do the same thing (for exhaust anyways). It's about the operator and prep.

-prep work is 90% of the weld
-ZERO gaps and backpurged with no filler is proper sanitary industry procedure for ss tube ~.065" but it doesn't look "baller" and takes more time to prep so very few people do it
-most people think any weld that has color is excellent when in reality it means squat from a functional standpoint
-color is technically contamination with the atmosphere but it's automotive and people like that kind of thing
-the outside of an exhaust only tells half the story
-the proper way is to backpurge the tube with argon so the backside of the weld doesn't react with the air in the tube. Without doing this you can't get full penetration and end up with "sugar" inside.

In the end it's a damn car exhaust and you can get by without backpurging and fitting with gaps and cheating bends. You won't be running milk through it and feeding it to your kids or going into space.

I shoved my camera into a Ferrari formula one header last year and this is how it should look. 100% penetration. They didn't use tube for this part of the header. It is flat sheet cut and then rolled into a cone to a certain angle and bend radius and then welded along the seam.