Originally Posted by dsaul

You should try it. The machine setup is the difficult part of AC TIG welding. DC is easy, because you just set the amps and weld. AC requires the correct AC balance setting (about 30% electrode positive or 70% electrode negative, depending on how your machine shows that value) , in order to get the right cleaning action and prevent your electrode from melting. Once you get that right, I found aluminum welding to be easier than thin walled chromoly steel. Everything happens slower with aluminum, so you have more time to see what is happening with the toes of the weld puddle and more time to feed the filler metal and advance it in your fingers. I'm not necessarily recommending building aluminum bicycle frames, but you should get some aluminum and practice. I think you will pick it up pretty quickly.

One thing to note, and I think it is the main reason for people having issues with the puddle suddenly melting away, is you need to physically remove the oxide layer on the surface of the aluminum just prior to welding. The oxide layer develops pretty quickly and its melting temperature is much higher than the aluminum. If you try to weld without removing the oxide layer, it will melt the aluminum under the surface before the oxide layer melts and then the whole mess just falls out when the oxide layer breaks. I prep my material by abrading it with scotch brite just before welding it.