MIg then tig question....

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Ok fellas I have a pretty simple question for you all.  Been building some things around the garage and usually utilize the mig to tack the pieces together and then use the tig to put the final welds in place.  THe problem I am having is when I get to the areas where the tach welded with the mig the TIG welding looks like crap.  when going over the mig welds trying to smooth them, I get a "sparckler" effect and lots of pitting.  I am assuming that its contamination - but the MIG welds look real clean and nice.  How do you guys handle this problem.  I see them using mig and tig all the time on shows - and wonder how they avoid this problem.  Thanks.Regards,Best Times with 434 Naturally Aspirated Vette60 - 1.261/8 -  6.37@ 107.25 MPH 1/4 - 10.08 & 134.9MPH1/4 - 9.60@144MPH
Reply:You have to clean, clean, clean - TIG welding anything that is dirty will cause lots of fireworks and sparks. Your basic tools - grinder, wire brush, acetone.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Brush and Acetone 2-3 times a day to maintain a healthy spark.ThermalArc 185MillerMatic 180 w/ AutosetVictor Cutskill Oxy/AcetyleneThermal Dynamics Cutmaster 38and spite!
Reply:THe only area that I have the problem in are the areas where I go over the mig (tack welds).....the other areas look perfect.  Bright, shiney and with no pitting. When I go over the tacks it looks like the 4th of july ....lol.  ANd the welds get downright UGLY.Best Times with 434 Naturally Aspirated Vette60 - 1.261/8 -  6.37@ 107.25 MPH 1/4 - 10.08 & 134.9MPH1/4 - 9.60@144MPH
Reply:Was the area cleaned before and after tacking?John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Maybe you need to touch those tacks with  a grinder, wire wheel or something.They should be fine after that.  The filler metal is close to the same.  Its gotta be contamination.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:If I have to tack with MIG, I will put new tacks in place with TIG, then go back and remove the MIG completely.
Reply:Yeah its weird, I welded all the other areas about 35" total and it all looks perfect, until I get to one of those buggers and then it looks like chit.  I will give them a good wire brush treatment and see what happens.  Other than that all is good.Regards,Best Times with 434 Naturally Aspirated Vette60 - 1.261/8 -  6.37@ 107.25 MPH 1/4 - 10.08 & 134.9MPH1/4 - 9.60@144MPH
Reply:if you look at all mig welds there is a glaze on the bead.  As stated before you need to grind the tacks and clean them before running tig over the top.I'm a Lover, Fighter, Wild horse Rider, and a pretty good welding man......
Reply:If you going to tig it afterwards, why don't you use your tig to tack it to begin with so less chance of contamination and chit? I know the mig is faster for just tacking but would help the final look of the job. Of course still cleaning them before final welding. Or is that a dumb suggestion?Latest Toys Miller 180 Mig and Elite Mask!!Wright Welder 225ACShop OutFitters 20/20 Bending SystemHypertherm 380 Plasma30 Years of Sparking (Electrical & Welding)
Reply:Just TIG the whole project Disclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:All good recommondations and will take them into consideration with the next project.  The things I have been working on were just "minor" things like my welding table etc.  Just trying to show the wife I needed both a MM210 and the synchro200  - so I tried to utilize them both.  Best Times with 434 Naturally Aspirated Vette60 - 1.261/8 -  6.37@ 107.25 MPH 1/4 - 10.08 & 134.9MPH1/4 - 9.60@144MPH
Reply:Originally Posted by WolfmanJack13If you going to tig it afterwards, why don't you use your tig to tack it to begin with so less chance of contamination and chit? I know the mig is faster for just tacking but would help the final look of the job. Of course still cleaning them before final welding. Or is that a dumb suggestion?
Reply:I've heard you can have the same problem when TIG welding over a Stick weld (SMAW), lots of bubblling, spitting, and porosity.  I suspect it may have something to do with a  higher dissolved oxygen/nitrogen content, or oxide/nitride content in the weld metal for some stick and MIG welds on steel.If you are MIG tacking with short arc and 100% CO2 it might make sense that the tack weld is less "sound", more crud in it and more likely to out-gas, than a spray MIG tack made with 92% Ar/ 8% CO2.
Reply:Scrub those mig tacks with a brush.  Mig wire contains a lot more "scavengers" in it than TIG rods do.  These scavengers allow mig welding to be done on less than perfectly clean metal, because the scavengers bring the contaminants up to the surface of the weld pool.  Chances are you're trying to weld right over top of these when you're tig welding."A winner isn't someone who doesn't lose, a winner is someone who doesn't quit."