do not use 6013... i am a welder and we refer to 6013 as garbage rod... because it is garbage... the first 2 number stand for the tensile strength of the steel in the rod and the third number describes what position the rod can be used to weld in 1= all positions 2= flat and horizontial positions 3= flat positions. for what your looking at doing you should run dc straight (DC-) which means the current comes from the machine and out of the electrode and into the ground. (DC+) is the opp.
Stick welding takes alot more skill but is alot stronger than a mig welder. I recommend using an 3/32 E7018 electrode at about 95 amps for tubing about 120 wall may be a little hot to learn on so adjust it if it is hot. I am a welder and we use 7018 or "lo hi" for complete x ray joints and structual welding. It is tried and true and been around for a long time. There is a reason why the dont use MIG (metal inert gas) for structual welding. it is easier but not as strong. everyone seems to think that the MIG process is the best of the best but it is not. You can have no skill and use a MIG welder and make a decent looking weld. Although A 220 mig welder is enough to create a good joint for a cage or sliders or whatever. but the 7018 will be stronger if done correctly
