To me a good tig welding machine is one that has a good crisp low amp start that wont blow holes in thin metal and wont melt the corner off thin sheet metal.
A good tig welding machine must also have high freq start, good duty cycle, and enough balls to weld the occasional aluminum block my machinist friend just crashed his tool changer into.
In a nutshell, Its got to have AC and DC current, good low amp starts, and plenty of sack.
Everything else, all the bells and whistles, are gravy...they are much appreciated , but not completely essential.
I figure one of the best ways to test out the low amp starting capability of a tig welding machine is to weld some aluminum cans...just welding beads on the bottom ridge will tell you what you need to know about a tig welding machine...whether it has a good low end or not.
I tried out 2 machines A Miller Dynasty 200dx
An Everlast Powertig 250ex
they both performed very well and both were able to light up on the can without nipping or blowing a hole...impressive.
Not all tig machines are able to start low enough not to melt aluminum that thin.
I also experimented with some pulse parameters that seemed to work pretty well for coke cans.
I figure if you need some good tig machine settings for thin aluminum, what better way than to weld on coke cans.
The settings that work good on thin aluminum coke cans will also work on other thin metal like .020", .032" .050" or .063". you just need more amperage.
So here are the settings that I settled on...
60 pps 30% on time of the peak pulse ( also called pulse width) 20% background 60 on the ac balance 90 hz ac frequency
The output was only about 12 amps but remember when using pulse, you need to set the main amperage higher because the output is an sort of an average of the peak and background