Advice on framework for a welding table

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I have a 2'x2' 5/16" thick steel plate that I want to use for my new welding table. The steel plate I was previously using was only about 8"x10". I purchased some 1.5"x1.5"x3/16" steel tube to make a framework fro the underside of the large plate. The framework was tacked up in one of those 90 degree clamps and finish welded on the small plate. One half of the frame was welded at a time. When I welded the two halves together on the small plate they were clamped down but there was alot of weight hanging off of the plate. The end result was that the framework was not flat. I do not plan on welding the large plate to the framework, just a couple of bolts so it can be replaced if need be. Can I just use washers under the plate to compensate or do I need to rebuild the framework? If I have to do it over, I'll weld up the tubing on the big plate this time. I'm new to welding so this is my first lesson in metal shrinkage
Reply:Please dont take offense but it comes down to whether you want it done or done right.  Each person has to draw their own line in the sand as to what level of perfect they strive for; lets face it perfection is a myth and yet we strive for it. My experience has been that by the time I get done screwing around trying to make something work right I could have started over and done it right from the start.
Reply:I agree with you on that. I'm a machinist and perfection often comes down to 0.0005", so learning welding I'm kind of picky on how acurate something is. I have alot of learning to do but a project is only as good as what it's built on. I will probably end up rebuilding the framework. What can I do this time to ensure it will be flat and square. Should I build it on the new table plate sitting on the garage floor and leave the joint opened up a little so it will shrink to square?
Reply:Here are some pictures of my failed attempt. Any comments good or bad are welcome. The welds were a mix of 7018 and 6013. The new tabletop is the plate leaning against the box in the first pic. Attached Images
Reply:My opinion only. If the large plate is nice and flat, grind down any welds in the framework tubing that will be in contact with the underside of the large plate (so you don't make contact with the crown of a bead).After you have done that, cut open the welds (saw or abrasive wheel)  on the side and bottom of the tubing (leaving intact the bead that sits against the table plate).Clamp the tubing framework into position on the large plate (using as many clamps as you can) and tack weld the tubing framework back together.After you have made all the tacks, then come back and weld your beads "one at a time" alternating to a different corner after completing each bead.This way you will minimize draw by keeping the total heat low and in just one spot at a time.Allow everything to cool until you can touch it barehanded mark a corner of the plate and the tubing so you can put the plate and the framework back together in the same orientation you welded in.Unclamp it and check the fit.  If it suits you after this, clamp it back up and drill your mounting holes through the plate and framework at the same time.  Or, you can drill holes separately in either piece you choose and transfer the hole pattern with transferring center punches.For you, (as a machinist) I probably put in too much info (on the hole drilling), but perhaps some other reader might need to know.Last edited by walkerweld; 05-13-2013 at 01:56 PM.
Reply:That is an idea. If I mess it up, oh whell now I have some extra tubing.
Reply:Sawing 3 sides loose will allow the tubing to bend (and assume a parallel orientation)across the uncut 4th side because the paltry 3/16" thick X 1-1/2" dimension remaining will be no match for the 2' X 2' X 5/16" plate you clamp it to.The only thing this trick can't account for is if you somehow had a "higher elevation" between any 2 of the tubular sections of framework when you welded it together in the first attempt.And I doubt that as you did at least have it positioned and leveled on the smaller flat plate (didn't you?).