Pos / Neg vs earth ground

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I'm new to MIG welding, and have a Hobart 140. I'm a bit confused about the pos and neg aspects. From the factory, the tip is ground, work clamp is positive.  So, if I want to weld on something that is physically mounted into the ground - do I simply reverse the polarity wiring? Any risk in doing so? Does this have any impact on the wire being 'cold' when the trigger isn't engaged?I need to weld some 1/8" flat bar to some steel posts. I'll be using a gas generator for power.
Reply:No. You only change the gun and clamp polarity when switching between MIG and flux core. Internally, your machine is only grounded on the power input side for safety. The output is isolated from input via the transformer inside the machine.Don't worry about the positive work clamp being in physical contact with the earth.PapaLincoln Idealarc 250 (circa 1962)Lincoln Weldpak 155 w/Mig KitLincoln Squarewave TIG 175
Reply:There is no 'ground' on your DC welders output side. Only positive and negative leads."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt