New to the tig, Need help!

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Hello, I'm James I'm a hobbiest at best but have always been interested in tig welding so after weeks of searching c-list I pulled the trigger on what I thought would be a good welding machine,It was a miller 250 hf dial arc( 82 vintage ) I have always loved my miller mig welder so I knew I could'nt go wrong and for $600 w/ bottle I took it home and now am trying to weld . I bought this for sheet steel or aluminum. The steel turns out ok  on a butt joint, a lap or corner... forget it, I just make a mess, then I tried aluminum I'm using a 3/32 2% thorated tung, #6 cup straight argon, on freshly cleaned 20 gauge aluminum (This machine has got a lot of switches an dials so bare w/ me ) I've reversed the polarity, set the dial to about 70 and the voltage switch to lowest of the  three settings  (this is the part that confuses me ) If I set the machine any lower it won't puddle and if I go any higher it melts the tungsten, (forget using the 1/16 tungsten, they just vaporize) I don't t want to blame the machine  cause I've never tigged before but any advice would be greatly appreciated, Thanks in advance.
Reply:Did you set the machine to AC?
Reply:I honestly can't tell by looking @ it. Ill study that miller pdf file owners man. again Can you tell by the pic?? Attached Images
Reply:The middle setting is A/C. You have it set on DC+ in the pic. That will definitely melt your tungsten.For alum. use A/C, for steel use DC- (top setting).That all refers to the switch farthest left."SOUTHPAW" A wise person learns from another persons mistakes;A smart person learns from their own mistakes;But, a stupid person.............never learns.
Reply:I thought that was the polarity switch but it was the ac/dc switch, this where I set it for sheet aluminum.
Reply:There is a middle!!!, ok  mystery solved, thanks
Reply:The switch just to the right of that, I would guess to be the balance control for the A/C. Not 100% positive though, since I can't really make out most of the symbols with that pic.
Reply:Originally Posted by jthawk71I thought that was the polarity switch but it was the ac/dc switch, this where I set it for sheet aluminum.
Reply:1) OK, careful of the advice you got here.  The machine is a Dialarc which is a sine wave machine - no balance control.2) Trying to learn aluminum welding on 20 guage is silly - pure frustration.  Grab a piece at least 1/8" or 3/16" if not a full 1/4".But if you insist...The lever on the far left is the polarity.  For most TIG you want it all the way up (DC-).  The exception is aluminum - for that you use AC (the middle position).The next lever from left is range.  For 20 gauge you want low range only (all the way down).The big dial is a percentage of what it says on the 2nd lever.  So if its like my older Dialarc, the low range is 10-45Amps AC setting.  You'll want about 35 Amps which is about 71% Start contactor set for remote.Amp control set for remote.HF set for continuous (all AC welding on a sinewave machine should have this).So for aluminum, you use AC setting and you use pure tungsten or zirconium tungsten.  Thoriated doesn't ball up like the other two - when it melts it melts ugly.  Since your machine is a sine wave machine without balance control you need to be more careful about electrode selection.No 6 cup is OK  15-17 cfh flow.  A no 4 cup go more for 15 cfh side.Personally I would be tempted to use a .040.  tungsten.  1/16 would be the maximum.This is all assuming welding in the flat on a relatively flat piece.Last edited by con_fuse9; 04-18-2010 at 06:31 PM.
Reply:All of what con-fuse9 said but to clarify the HF setting, it should be 'continous' for aluminum only and 'start' when you go back to DC for steel.  Just make it a habit when you switch the current (AC/DC) reach over and change the HF switch.Have fun! and 20ga aluminum would be frustrating for you, get a chunk that you can screw up with authority and have at it!