Miller 30A spool gun

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I have the above gun on my Millermatic 250X. I bought everything new ?? years ago and the welder works fine. I have not used the spool gun for prolly 10 years and when I did (a long time ago) it worked fine. Well a little alum. project has come up and when I "trigger" the Sp Gun I have wire and gas but no arc. Been looking around on Miller's site and it seems that an answer from you guy's might be faster. One thing that I do not know and may have screwed up while changing gun polarity for flux core is the location/hook up of the wire to the Sp Gun. Right now it's on the - stud with the ground clamp. My initial GUESS is that is wrong and needs to be moved to the + stud but I'm skeerrd to do it without asking the real welders. While I am asking for advice, I'm welding some .250 alum (5052) H32? brand new & clean. Do I need to do any other cleaning or brushing, prep? It's a $300+ 4x12 sheet that just about every inch is "spoken for" in this project. Thanks,
Reply:Yup. If I've read your setup description right, you need to change the spool gun power cable to the (+) output stud.  By having it connected to the (-) along with the work clamp, you don't have a complete weld circuit.SS wire brush and wipe down with acetone.  Even new material has a micro thin layer of oxidation that needs to be removed prior to welding.  MIG is more tolerable of it but it should still be cleaned away first.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:That was it Duane, thanks. It looked like the problem but I didn't want to fry anything. Alum sure is a different animal all together. I'm getting stuff to stick ok. Now  I need practice. I used a recommended setting that I found here on weldweb  and I think it was "spraying", at least it looked like it. Toasted a tip in the gun! I slowed things down 19.5 v @ about 360 ish wire speed. The wire that I have is 5356 and read that the 4043 is popular. Is there a big diff between the two?
Reply:Due to the added heat when running aluminum properly in spray mode, you'll need to maintain a slightly longer stick out of 3/8" or more, a little higher gas flow (25-30cfh) and faster WFS to help prevent problems with tips.  Keeping the tip slightly recessed (1/8") inside the nozzle helps too.WFS and filler wire size obviously plays a roll in the proper voltage setting for spray mode but voltage would normally be in the 22-26V range and WFS set accordingly.  Travel speed will be faster than short circuit mode with other metals.As for the 5356-vs-4043 question, I refer you to this:http://www.lincolnelectric.com/en-us...re-detail.aspxMM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!