I'm working on a plasma table (it's under the custom shop tool category). This is my first big welding project. I've done a cart and a bunch of little things, but nothing on this scale.
I used 2" 14 ga square tube for the frame. I MIG welded 2" x 1/8 flat bar around the bottom of the square tube. One edge was centered on the square tube. This gave me 1" protruding on the inside. I used this for the bottom on the water table.
The problem I had was that after I welded the 2" bar the 2" square tube got a pretty serious arc to it. It was about 3/4" higher in the middle than the ends on a 6' 6" run.
For the future...... What can you do to avoid this?