Welding Tips and Tricks

I am making a cabinet with drawers and I am putting a 3/16" top on it. I've added a 8 inch piece (X30 in) to a 48 X 30 inch top. I have a stick, tig and mig welder (only .025 wire). I attached the 8 inch piece and tig tack welded it about every 6 inches on the front and back. I straightened it pretty well, and then I put about a 12-18 bead using the mig on spray (about 22v and about 550 in/minute). It warped it pretty good. I got my gas torch out and went over the weld and it like popped right back to where it was again. It's just a top, and it's pretty straight again, but I was wondering what is the best procedure? Should I back step the welding doing a 3-4 inch long bead using my tig, or mig or what? I guess I put a lot of heat in a relatively small area when I welded it with the mig on a high setting. Should I use the mig on short circuit or just tig it, both sides, using back stepping or what is the best procedure. It's mild steel. The gas torch really fixed it the first time, I guess because I heated up a fairly large area and let it cool slowly.
Thanks for any information, I'm just a hobby welder.

Clamp it tight, do small stitches, and move around to avoid heat soaking it. You also might let it cool a bit between welds. Large chill blocks clamped down to it also help.

Thanks Weldmonger,
I went and tried to make the plate even more flat, and I screwed up. I made the thing so dished, that I cut the offending 8" piece off, and I think I will be able to make the big piece flat by bolting it to my cabinet (thankfully made of steel tubing) I think after I get that piece bolted on, I will cut another 8" piece and try it again.
I know if you take a beam (or any substantial thickness of metal) and heat it red hot, that it will expand, but will press against the back side of the metal (unless that is red hot too). Since the metal has no place to move it will actually bend a little and when it cools, it will be dished in the direction that the heat came from) concave to the heat source. I know if you want to avoid the weld being brittle (if it has a high iron equivalence) you can heat the whole thing up, to heat it to cool slowly. Does this entire heating thing help also to avoid distortion? I don't have a 'rosebud' to get the entire thing hot, though.
I think I will tack it together again (w/ new 8" piece on end) and then do the stitch thing as your reply says.
Thanks for the info!

I would not heat the entire piece. You’ll never get it hot enough to prevent warpage as the welding will be twice as hot. The disparity in heat will exacerbate the distortion.

Clamping it down tight after racking helps. Also, patience will help. You can air coil it too since it’s decorative and not structural. Take your time, skip around, 2” stitched. You’ll be fine. Let it cool completely while clamped. Then cut the tacks free.