[abianco37772]

Hello, I'm thinking about putting together a scratch start tig rig as a gift for my brother this christmas. I can get my hands on an AC stick machine for $50 so I'm wondering; is it necessary to build a rectifier? What's the beef with tig welding carbon steel using AC? Does it have to be DCEN? Why?

[rake]

Rectifier? Yes.

DCEN why? Direction of current flow. On DCEP the current will flow from the base metal to the tungsten.
Translation, the heat will build up in the tungsten and melt it away.

It isn't all that hard to build a rectifier.

[dynasty200sd]

The situation you run into when TIG welding in alternating current is the arc wanting to extinguish when the polarity switches from negative to positive. This is why you see high frequency built into TIG welders to prevent the arc from extinguishing.

[MinnesotaDave]

You'll be money ahead to just find an AC/DC welder for about $200 in my opinion.

Then buy a torch and flow meter, about $125 and $35, and you're all set.

Sometimes it doesn't really pay to tinker in my opinion - cool idea for a gift

Side note, the ESAB 161 is a very nice stick/tig package.