Cut a piece of 3/16 plate for a base and it bowed on me
Not the weld. The plate. I cut a 14 inch square of 3/16 for a base, sat it on the bench, and it rocked. Ran a straightedge across it and there's a belly in the middle maybe an eighth. It was flat when I bought it, or flat enough that I didn't check, which is the part I'm annoyed about. Twenty years ago I'd have tacked it to a strongback before cutting and not thought twice. Today I got in a hurry.
Two options. Heat it and shrink the belly out, which is fussy and I've never been great at it, or cut another one and clamp it down this time. I'll probably do the second one and keep the first as a shim under the bench for the next ten years, which is what happens to half the steel in this shop.
The metal doesn't care how long you've been doing this.
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the belly is from the cut releasing whatever stress was rolled into the sheet, so clamping the new one down won't fix it either unless you clamp it while it cools and hope. honestly i'd keep the bowed one and let it be a base for something that doesn't need to sit flat, that eighth is a feature if you stop fighting it. heat shrinking is a whole evening and it'll still never be dead flat.
The "clamp it while it cools" part is the bit people skip. Clamping cold plate flat just means it springs back when you let go, so either you leave the clamps on forever or you accept it. I'd agree with keeping the bowed one, though I'd say it plainly: an eighth over 14 inches is not a flaw to negotiate with, it's just what the material did. Put it under something that sits on three points and forget it.
Fair enough. An eighth is an eighth, and it's not going anywhere. I'll put it under the welder's vise and let it be a base for something that doesn't care.
The clamp-while-cooling point is the one I keep going back and forth on. If I clamp it hot and it holds, fine. If I clamp it cold I'm just storing energy in it. Cutting the next one oversized and trimming after is the honest fix, and I already said as much above. Should have done that the first time.
You're right about the stress, and I knew it when I wrote the post. Clamping won't take it out, it just holds it while I pretend. What I should have done is leave the piece oversized and cut it after it moved, or tacked it to the strongback first like I said. Cutting first and clamping after is closing the barn door.
The bowed one's not going in the scrap pile. It'll do fine under something that sits on a foot anyway, nobody's putting a level on the underside.
Only thing I'd argue with is the heat shrinking. It's an evening, sure, but shrinking a belly in a small square is about the most forgiving heat work there is. Not dead flat, no, but closer than it is now. I've got a rosebud and a wet rag and I've wasted worse evenings.