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Crown in 1/2" Plate

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  • Crown in 1/2" Plate

    I'm building a small welding table and ordered a piece of 1/2" plate 2' x 4' from the local supplier. The first plate they sent was crowned 3/16 on the 4' dimension so they replaced with a second drop. It's the same way and I assumed it was created by the heat from cutting off this drop. I'd like to get it as flat as possible before tacking to the frame.
    Read some posts on here and last night I clamped the piece down to the frame and ran about 10 beads 3" long on the crowned side as was illustrated. Kept my voltage on the low side to not go overboard. It didn't have much effect on the crown I was trying to correct on the 4' dimension. I now have about a 3/16" crown (where I started) on the 4' dimension and a 3/8" crown on the 2' dimension. Can anyone offer any suggestions on what I can do to get this piece flat? I'm going to use a rosebud this time as it's a pita grinding off the beads. Also, should I clamp as before (think this might have caused the crown on the 2' dimension) or just let it "float" on top of the frame. Or, should I just forget trying to get it flat, tack down to the frame and start using?
    Thanks for your input.

  • #2
    Did you put the crown down or up? I had the same issue with my 4'x4'x3/8" table. I didn't want to weld on the top any more than needed so i made a frame from 3x3 angle and added the legs. Then i put the plate onto the frame with the crown down and pulled the edges down with clamps and tacked the top to the frame along the outside edges and it it nice and flat...Bob
    Bob Wright


    • #3
      It's hard to say with out seeing this in person. Bob's idea is good & probably the best for someone untrained.

      What could be happenning is when the plate is flamecut the edges actually shrink in the haz which causes the center to bulge. It could also have been from the mill & just did not get flattened enough. Then by welding in the wrong spot you caused it to bow the other way. When you heat metal it will shrink when it cools. You need to counteract this.

      Heat the center to try to shrink it. You could make it worse by heating in the wrong place or wrong side.

      Find a shop with a hydraulic press brake that can do 1/2" plate (200 ton or bigger) & have them flatten it.
      Last edited by MMW; 04-06-2012, 05:12 AM.
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      • #4
        I ran the weld beads on the convex side (crown up). I've since been working on it with the rosebud and it has flattened out in the middle of the 4' dimension where heat was applied. Still cupped on both ends so I put some heat there before I left for work this morning. Guess I'll see if I made any progress when I get home. If it's still curled I'll flip the plate clamp it down and tack in place as has been suggested. Thanks all for your input!