First of all I would not use a mig welder to do frame work. The welds don't really get enough penetration into the base metal without quite a bit of practice. If you use a stick welder I would 7018 just because it will make it easier for you to strike an arc and get a good bead. I don't know how much welding experience you have so I would suggest running two passes on everything just to make sure you get good base metal penetration and a good solid weld. Run the machine at about 125-130 amps and practic a little bit with the travel speed until you get a nice convex looking bead. The size of the tubing doesn't matter as much as the wall thickness does, this is what would determine what type of welder I would use. Good luck. Just drop me a line of you need any advice or anything.
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