I like this way of jacking up the table.
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Do a search for welding tables on the Garage Journal forum, get comfy, and read for a few days. You'd be amazed at what the guys over there come up with. The way they document and explain everything is great too.
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Whatever size you do choose, take the top plate in to a water jet service and have a hole grid put in it. This way you can drop in JIGS anywhere on the table and use bolts to clamp projects down. I just had mine done for a 7/16-14 heli coil.
Any advantages to A36 alloy vs regular carbon plate?
Now thinking C 6 x 8.2 for a 6.5x3.5' frame under the table.