I've been making some brick trays to cover existing manholes. I've got 3mm x 50mm x 50mm angle for the frame, mitred and stick welded together. I was quite pleased with that. I had some 2mm plate to fill the interior (450mm x 900mm) which I've MIG'd all round, both for the practice and so that the brick-bedding sand doesn't run out. The plate now has a warp set into it which must be because I didn't go slowly enough to let the heat dissipate. If one steps on it, there's a great bang as it bends out the other way. This would be fine if the weight of the bricks kept it down, but they don't. Short of cutting around the whole thing and welding it again, can I release the tension with a torch, or perhaps put a bar across for strength? I had hoped that welding the plate to the frame would give it some of the strength of the flanges on the angle, but obviously that was pie in the sky.