Hi Dave,

Im a hobby welder, have a 175 miller matic. So far my take on mig welding is that the penetration is not as good as stick but this can be overcome with preparation.

You will want to V the plate. If you are in situations where this is not possible use Flux core. Flux core polarty should be wire negative. This puts more heat into the plate and gives better penetration.

I thought flux core would be nasty compared to solid wire with gas. Bought some and was pleasantly surprised. Flux core costs more.

Dave P.

it's not so much a question of wire thickness...it's a question of how many amps are going through the wire. .030 wire will handle 130 amps. the reason it can run that many amps through it w/o melting is because it takes time for it to heat up to the melting point. if your wire feed speed is set right, the wire will not melt before it comes in contact (short-circuits) w/ the base metal. if the feed speed is set too slowly, then the wire will melt before it touches resulting in the wire fusing to the contact tip. in fact, .035 wire is the largest wire size recommended for out of position welding on ANY thickness of steel, provided you have the available amperage to penetrate to the root. there are 300 amp MIG welders out there that only have .035 wire in them because if you have wire any thicker it'll make a bead that's too hard to control when you're welding overhead.

also, you can weld any thickness of steel in any position w/ 1/8" 7018 and at least 140 amps...so the thickness of the rod doesn't necessarily have to be the same as the base metal thickness.
anyway...hope that helps you.