While searching for this topic I found a discussion on the MillerWeld website that covers the same issues. I think it is worthwhile to read the replies there , particularly on page two.
http://www.millerwelds.com/resources...lease%29/page2
The bottom line (in my interp) is that grounding various pieces of equipment or the table to separate ground rods won't work since they are all at slightly different voltage potentials and as such will generate various 'swirling' currents. If you insist on grounding multiple items or building Faraday cages, they must all go back to the neutral bar of the building's electrical service.