220V to 110V converter

So "how" do I get away with using a 3 terminal plug (no neutral) for occasional 120V and WHY would I do that?

FIRST, at my junkhouse, the 240V welder box comes DIRECTLY off the main breaker box. AT THE MAIN BOX the is where main power comes in, and the neutral buss, and the ground buss and the box ground ALL AMOUNT TO THE SAME TERMINAL. This is NOT the case with added breaker boxes / sub panel such as "over at the house." (My main is at the detached garage)

At the house breaker box, which in this case is actually a sub-panel, the box is grounded to a stake, and is grounded to a ground / green conductor coming from the garage. The NEUTRAL at the house box is connected to an INSULATED neutral buss bar, NOT THE CASE at the garage main panel

If you open my box, there is about 2ft total wire "or less" between the box for the welder, the main box, the neutral, and the ground buss. They are one and the SAME

So I have "cheated" and tied the neutral and ground together on my 120V adapter. They are one and the same.

I ONLY do this when I want to use the 120V MIG "far from" the house, as I have a couple of long "welder" extension cables

This is NEVER plugged in for more than long enough to get the job done, certainly not unattended or overnight.

So far as grounding, it is safe because everything that is a "box" is grounded including the welder, which ALSO has a 3 wire plug