steel thickness

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Hi, this is my first post. I learned how to mig weld a few years back and welded alot of stuff around the house. For example, i welded some sheet metal in the bed of an old dump truck i had. I've never done any other kind of welding and so i dont know a whole lot about it. Im about to start a project here pretty soon and i'm going to be doing some welding and had a question about what i can weld with a mig welder. I've noticed on the chart that is on the welder it gives metal thickness that you can weld. The project im going to be doing will be 1/4" steel and on some parts up to 1/2". My question is can i weld that 1/4" and 1/2" stuff with that mig welder and expect it to be a good weld? Last year when i was doing a little welding i also welded a hitch to the back of the dump truck and i welded some 1/4" and bigger stuff and it held up, but is there any reason i should weld it some other way? thanks in advance for any response. Zack
Reply:How many amps does your MIG put out?   I weld 1/4" with a 200 amp MIG and it welds it fine, however anything much thicker than that is too thick to do in one pass.   To weld the thick stuff, I grind a bevel on each side of the joint to be welded, gap them apart a little and weld it multiple passes untill the weld fills up the joint.   That method of welding thick steel can be used with any welding process too (MIG, stick, TIG).
Reply:I'm not sure about the amps, i borrow the welder from my wife's mother's fiance so im not too sure about the amps. I remember welding 1/4" steel when i welded that hitch and i would let the weld puddle up then make passes back and forth and it seemed like a pretty good weld. If the welder is less than 200 amps do you think im going to have a problem welding the bigger stuff?
Reply:Quick ballpark rule-of-thumb for welding steel:Use one amp for every 0.001 inch of steel thickness.So, for 1/4 inch steel, since 1/4 inch is 0.250 inch, you are looking at 250 amps.Good experienced welders and doing multiple passes on the weld or doing other 'tricks', like double-bevel edge prep and welding from both sides, can extend that amperage-to-thickness range a good bit.
Reply:The above estimate doesn't sound right to me. Many of the Miller and Hobart machines that are rated at 150 amps are spec'd on their sheets as doing 3/8" steel and their other machines rated at 200 amps are spec'd for 1/2" steel. I'm not saying you're wrong, but that "rule of thumb" just doesn't jive with manufacturers specifications.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Double-bevel weld from both sides and/or multipass welding.  It's usually in the fine print on the spec charts.Example,  the Miller manual for the 135/175 lists 125 amps for 1/8 steel material, see page 35, the PDF is here :http://www.millerwelds.com/om/o1324k_mil.pdf
Reply:Ya, the fine print within always has a catcher.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:You could run 95/5 gas which will put it in spray transfer. You WILL get penetration there.
Reply:Here's a simple question.  What kind of plug is on the welder??  if i's a 120V plug,  you can expect 1/4" max without a lot of beveling and multi pass...  oh yeah consider using fulx core for the thicker stuf it runs hotter.