Newbie with MM200 and 30a spool gun working but question on how to measure output dc

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Hi guys,  I am a newbie to the form. Thank you for everyones input and help in getting my vintage mm 200 and new miller 20a pro spool gun working from another thread here.  works great but I have two important questions that I really need help with from the group.  I am welding only aluminum 1/4 thick, 3/8 thick and some 1/2 thick plate.  Here are my questions I cant seem to figure out.  1. How can I measure the dc voltage output of my mig machine on any given setting? My old machine has not digital displays just a rotary setting for power and wire speed.    I need to know the exact dc output voltage of these settings to be sure I that I am in the spray transfer ballpark.  Can I simply attach my meter in DC voltage setting with the positive lead to the center electrode aluminum wire and the negative lead to my work piece ground and pull  the trigger on my spool gun or will the machine strike and ark and weld my meter to the bench?  There must be a simple way to make or connect a voltmeter to am older but good machine like mine?2.  My second question is on on the 100 percent Argon shielding gas that I am using with 4043 .047 diameter wire welding 1/2' thick aluminum plate// should my as flow rate be 35 cfm ,minimums? Higher ?   its a bit confusing.. Seems when I drop my flow lower than 20 cfm I get black soot.  Any and all help here is super appreciated.  Thank you. J
Reply:You don't need a meter to know you're in spray mode.  You tell from the sound.  When spray is achieved you will hear a whoshing sound almost like a small air leak rather than a crackling, frying bacon sound.For the material thickness you're dealing with I predict you will need to be on at least 5/High if not 6/High and adjust the wire feed speed accordingly to prevent wire burn back to the tip.Your argon rate is probably close to spot on and I typically run 25-30cfh with my SM-1 spoolgun for aluminum.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:I agree with Duane except that if your welding 1/4" to 1/4" the settings might be a bit high, in that case high 2 or 3 might be more apropriate. You need to set the power settings closer to the thicker material settings when welding different thicknesses together. That is an awesome setup you have and should work well for you. Also push your welds rather than pull to reduce soot.Yeah, I know, but it'll be ok!Lincoln Square wave 255Miller Vintage mig30a spoolgunThermal Dynamics Pacmaster 100xl plasmaSmith mc torchEllis 1600 band saw
Reply:Thank you guys for the help.  I will use the settings advice. cool...thx again. J