SMAW would be My preference, how critical is the application?
Welded 2 bits of 12mm a couple of weeks back. Gussets on a bag lift for a farmer.
Manual mode, 1.2mm wire, everything up to maximum. Hasn’t fallen apart yet, and it lifts 2.4t quite often..
Waiting for the AC/DC Rebel to come to the U.K., and may “upgrade”, alternatively it’ll be the 320ic
If it’s over engineered so there’s no flexing in it and you’re a competent welder then you should have no issues, stick welding would be my choice unless you think you’re going to get too much distortion...Thinking of building a new head for a Bridgeport manual mill converted to CNC - from the column upwards including the Z axis, would be U section weldments I think, early stages yet.