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Hi DS, First question I would ask does the WPS (welding procedure specifiction) allow the use of Mig? If not then you will need to consult the Welding Engineer for there approval. I always use a left to right travel as then I can see the total molten puddle as I have a left dominate eye. Although 100%Ar can be used, 75%Ar25%He adds more arc stability with deeper pentaration which is desirable for AL welding at about 40cft/hr. Although Mig short arc will work well for 1/4" AL, Mig spray arc is that much better as the molten transfer and arc stability is smoother. Mig-SA then you want a spool gun with a CV machine with a 60% duty cycle at 250a. For high work the ideal machine is one that has voltage and slope controls on the spool gun. With the newer machines I would bet that slope control is no longer needed. Without using any of the newer machines, it's hard for me to say what brand but 20yrs ago my choice would be Miller then Lincoln. In any event stay away from the cheap machines while welding AL. Welding Fe is alot more forgiving than welding Al. You can speed up your Tig (wet torch) welding with using a different techinque. Use a #10 short cup and rocking in your weld. Rocking the weld is where you establish the arc then place your cup lip on the V grove edge and rock the cup in side to side while at the same time twisting (turning) the torch just slightly at a angle to move the cup forward. The Filler rod is layed into the V and not moved. With the correct heat setting and filler rod diameter and rocking motion, As the torch is moves forward (rocked) it burns off just the correct amount of filler thus filling the V. Besure and ball your 100% tungsten using a piece of copper. Sharpen the tungsten to a sharp point then using DCEN on a copper bar thus forming a ball on the tip. As with any AL welding I can't stress enough keeping the weld joint VERY clean with a "new" powered SS wire wheel. T_Bone
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