MIG wire size & difference ??

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Hi all :-)I am still a rank novice on my newly aquired MIG welder. It was from a farm clearance sale and came with a near full roll of what I think is 1.2 mm wire (label has come off !)My question is: Just for general welding around my workshop, most projects would be on mild steel from about 2 mm up to 6 mm (every now and then I may weld thicker stuff), is this 1.2 mm wire an overkill ?Is it harder or easier to weld on smaller wires of say .9 mm or .8 mm  ?I use gas with my MIG as well.
Reply:I don't think in metric, but if I remember right, 0.8mm is .030" wire and 0.9mm is .035" wire.   Let's see, there are 25.4mm per inch, so 1.2mm would be about .047" or 3/64" wire.   I'm guessing 2mm plate would be about 14 ga and 6mm works out to be about a little under 1/4".Any of the wires you mention, 0.8mm, 0.9mm and 1.2mm are suitable for your use, with the 1.2mm being a bit big for the thinner metal.  The 0.8mm and 0.9mm are better for the thinner end and middle of your stated range of thicknesses and the 1.2mm is ok for the thicker end.  The .035" (0.9mm) covers the full 2mm to 6mm thickness range you want to do and is what I use most for solid wire and gas on that thickness range.   I would save the 1.2mm wire for welding thicker metal (above 6mm, provided your machine has the power to run that wire and plate thickness).You will need to change to the right size tip and drive rollers to use the 0.8/0.9mm wire in the machine, and possibly change the gun liner as well, if the machine has been properly set up to run the 1.2mm wire.Last edited by DesertRider33; 03-05-2009 at 05:14 AM.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Thanks for that. I forget you guys are on imperial measure (thanks for converting).My welder is 210 amps.I think I may get a spool and new tips for .9 mm and do as you say and keep the 1.2 mm for the bigger stuff.
Reply:I agree with DesertRider33 that .9mm (.035) wire would be the best fit for the thickness you're welding.  You said you are using gas with it.  Using 100% CO2 is the cheapest way to go, but it will give you alot of spatter.  75/25 (75% Argon mixed with 25% CO2) is a little more expensive but will give you a better looking bead with less spatter.Good Luck.Welding is my hobby, I just happen to get paid for it!
Reply:Originally Posted by eyspyThanks for that. I forget you guys are on imperial measure (thanks for converting).My welder is 210 amps.I think I may get a spool and new tips for .9 mm and do as you say and keep the 1.2 mm for the bigger stuff.