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Just got mysalf a new gas gsaless mig welder. The welder was set out off the box
for gasless wire polarity + to earth. I purchased one of those desposible argon co2 bottels
from Bunnings to run it on gas so I changed the polarity to - earth. (Those bottles dont last very long
,about 15 mins). My question is Whan l put the gasless wire back in the welder l forgot to change the polarity back,
It did not make a difference ,l think to the weld. The hand book does nt say why it should be changed
So why should it be changed?

When u change it to gasless it gives a hotter weld. Less chance of blowing holes and less splatter. Someone will have to back me up on this on.

also depends on the wire some wire is polarised, what metal your are welding the gas your using (some flux cored wire use gas) the main reason is becuase it can damage the welder if you dont have the right polarisation to match the wire with gas less wire this is most important a mate had to replace the circuit board in his because someone put it on the wrong polarity. as for giving a hotter weld with migs i don"t know. but reverse polarity with a stick welder put the heat in the work (what your welding) not the electrode (the welding rod) less chance of blowing holes because of a more even spread of heat in your work.