These sizes would be a little big for my lathe and vice but I quite often make dome caps for smaller tube in SS and Alu.4" and 5" OD with a 3mm wall.
This is what I suggested apart from forming it into a dome before welding.Can you not cut a disc out to OD required in thickness wanted and then weld on? Or is it a removable thing?
Yeah I didn't get it first readThis is what I suggested apart from forming it into a dome before welding.
It's a fairly simple thing to do especially in Alu.