I visited a metal working company while I was in grad school that had an awesome system for welding – They had these huge table that was a steel grid on about 3” centers. Where the framing members joined there were holes available for hold down clamps. While I haven’t yet created a plan to build a table like this in the shop, I was browsing the latest copy of Machine Design and came across a company that has a wide variety of clamps. As there are a variety of other theatrical uses for these clamps I thought I would pass the link on.
Their site also has a variety of useful reference material available here