Hello Dave, everyone that has responded to your questions has given you great suggestions on things to look for and to try. You mentioned in one of your sentences something about seeing a purple color in the arc. My experiences with colors in the arc when welding aluminum typically indicate that the purple color indicates the presence of magnesium. Is there any possibility that any of the rods that you are using could possibly have been mixed in with some magnesium filler rods? Most of the time when the filler is of a 5356 grade the arc colors will be somewhat greenish and if the filler is a 4043 grade the arc color may be more of a pink hue. Another thing about trying to weld aluminum base material with magnesium rod, the weld will not fuse readily and if a bead is formed it may fall out of the joint in one long piece when any sort of force is applied to it. You can check the filler rod you are using and any type of base material that you are welding on for the presence of magnesium by getting ahold of a solution of silver nitrate and putting a drop of it on the material, if the drop turns black there is magnesium present, if the drop stays clear it is aluminum. A question for you, when you first try to form the puddle before you add filler rod does the puddle cloud immediately and does the area immediately surrounding the puddle show no indication of the HF cleaning action of the oxides? If so that is a pretty good indicator of possible shielding gas problems or possibly DC reverse polarity current being present instead of AC. Initially my suggestion for you would be to very carefully check all of your initial machine set-up hookups and connections, proper polarity, tight gas connections at all fittings and no gas leaks, proper assembly of torch components,(tungsten collet inserted in the proper direction, all parts included in the assembly of the torch head,spacers,o-rings,any other gaskets), I had the experience of putting the collet in backwards on one particular style of torch and even though you could hear the flow of gas and feel it, it disrupted the flow in such a way that it would not shield properly, once it was installed in the correct direction everything worked perfectly. Along this same vein, make sure that your collet parts are for the specific diameter of tungsten that you are using, some torches have different components for each different diameter of tungsten that can be used. Make sure that you are using the proper flow rate for the particular size of cup that you are using on your torch, smaller cups require reduced flow rates when compared to larger cups. As one of the other posters stated, an incorrect flow rate can create turbulence that will actually draw the surrounding atmosphere into the weld zone when the flow is too high and obviously if the flow is too low there will be insufficient gas to shield the weld zone properly. One other question, when you have tried to start the weld and run a bead and then stopped welding or trying to weld is the tungsten maintaining the the ball that you started with and is the tungsten still shiny without any indication of oxidation or blackening? If the tungsten is staying shiny that would be an indication that your gas shield is performing properly, if not, it would indicate that there is a likely gas issue. Here again the answers to those questions would point you in the direction of equipment problem or material or filler issues. One more thing, when you are welding are you keeping an eye on where all of your leads, gas lines and related components are? The reason that I bring this up has to do with having kinks in gas lines because they snag on things, having things laying on top of the gas supply line causing a lack of gas, having hot parts, sparks or other things put holes in the gas supply line, even setting the leg of your welding stool on the line cutting the supply of gas off that way. Sorry for the long winded response, I'll be curious to learn what you find to be the problem. Regards, aevald