MIG Welding wire size selection

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What is the thumb rule for selecting the SIZE of MIG wires for various applications?
Reply:Well the rules of thumb for selecting mig wires are about as usefull as the rules of thumb for driving. Too many variables to be of much use other than drive slower on slick or icy roads or any other time it's not safe to drive fast. There are some very general charts based on something close to full penetration citing things like 1 amp required for every .001 inch of material, and some charts showing the amp maximums/minimums of wire sizes in general and charts showing amps delivered per inch of feed for each size. Some of the simpler ones are manufacturer specific, either wire or machine and are much like bar charts. Go check lincolnelectric dot com or maybe the manu of your particular welder. So many types of wire, gas mix and weld fit ups charts just don't do much for ya. .023 has about a 90 amp max, .030 around 145 and .035 about 180
Reply:It really depends on the welder, the process (short circuit or spray), the thickness of the material, the desired current to achieve penetration and the amount of fill.  There aren't any universal rules of thumb, but most welders come with a door chart that will get you pretty close.  Alternatively, you can check a welding manual for a chart.At a given voltage and feed speed there's going to be a certain amount of current and a certain deposition rate for each wire size.  For a particular class of welder, there's going to be a certain wire size that works well within the range of the welder allowing for the greatest level of control.