Question about flattening out plate

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I had a piece of 1/8" steel plate, and I decided to start building a roof for my wife's Polaris rzr.  When I got the sheet on my fab table I noticed it has a bow in the sheet.  How would y'all attempt to flatten it? Just heat and beat, or heat and sandwich between my table and a heavier piece of plate?  I don't do a of sheet metal work so I would appreciate any advise.  ThanksMiller BobcatHarris cutting outfitMiller spectrum 625 plasmaVariety of shopmade tools
Reply:How bad is the bow, and how are you planning on attaching it?  Bolting down may exert enough force to pull it into shape.That is a pretty heavy plate to attempt to do any stretching or shrinking if you have no experience. If you can cut the plate to size so that the plate is bowed evenly, you would probably be better off trying to make it work the way it is. If you have a decent size hammer you can work around the perimeter to stretch it out, but you will need a heavier plate laying under it on a concrete floor to act as your anvil. If you go about it bass ackwards you will only make it worse.
Reply:Originally Posted by Pro-FabHow bad is the bow, and how are you planning on attaching it?  Bolting down may exert enough force to pull it into shape.That is a pretty heavy plate to attempt to do any stretching or shrinking if you have no experience. If you can cut the plate to size so that the plate is bowed evenly, you would probably be better off trying to make it work the way it is. If you have a decent size hammer you can work around the perimeter to stretch it out, but you will need a heavier plate laying under it on a concrete floor to act as your anvil. If you go about it bass ackwards you will only make it worse.
Reply:You're best bet is to make the roof first and do any cutting, welding and bolting that needs to be done.  Then if it is still bent, you can likely support it on 2x4's and stand on it to straighten it back out.Don't heat it, with no experience on such thin material you're just going to make it worse then it is.  Heat straightening is part science, part art, and mostly luck.Have we all gone mad?
Reply:Originally Posted by jw3Thanks, which side would u heat ?(the hump or the dent).  I was thinking of putting the 1/8" plate on my 1/4" table ,heat the 1/8", then putting sum3/8" plate on top of the 1/8", and clamping securely until the 1/8" cools.  Do y'all think it would work.
Reply:Originally Posted by jw3Thanks, which side would u heat ?(the hump or the dent).  I was thinking of putting the 1/8" plate on my 1/4" table ,heat the 1/8", then putting sum3/8" plate on top of the 1/8", and clamping securely until the 1/8" cools.  Do y'all think it would work.
Reply:!/8 inch plate is real overkill on such a small vehicle.WOW! !/8 plate weighs 5lbs. per square foot.If you heat metal when it cools down and it shrinks.A 3 foot by 3 foot plate would weigh 45 lbs.,!Last edited by Donald Branscom; 04-05-2011 at 10:35 AM.AWS certified welding inspectorAWS certified welder
Reply:Originally Posted by Donald Branscom!/8 inch plate is real overkill on such a small vehicle.WOW! !/8 plate weighs 5lbs. per square foot.If you heat metal when it cools down and it shrinks.A 3 foot by 3 foot plate would weigh 45 lbs.,!
Reply:For heat shrinking plate there are different techniques / methods. For thin small sections of plate I like to use a welding tip on an O/A torch, start in the middle of the hump and heat a series of dull red small circles. Being very careful not to use too much heat! Sometimes I'll let it cool naturally, other times I'll use a spray bottle of water. For thick large sections of plate I'll use either a cutting tip or rose bud, and heat stripes. And use a water hose to cool. Attached ImagesDon’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:the method i would use is on the hump side start in the center and heat in and ever widening circle like a spiral watching the metal as it moves to straighten until the desired effect is complete. then i would blow low pressure compressed air on it to cool it slowly following the same circle pattern.225NT bobcatAEAD200LEScott 125mm175, mm252 w 30A, PT225mm211, TA 181iHyper Therm 380, cut master 529100X & XX, Digital Elite6 Victor setssmith little torch, meco midget kalamazoo band sawsteel max saw evoulution circular saw
Reply:In the grand scheme of things, 1/8" sheet is pretty easy to bend, I personally wouldn't bother with heat (although you've got some good advice on how to do it that way), I'd most likely either put it on some wooden blocks and  hit it with a sledge (don't hit the sheet directly with the hammer, use wood) , clamp a bit of box with spacers to the bench and bend it by hand (depending on the size/length of the sheet), wedge it between a pipe and the wall and pull on it, or just tweak it with the press (if you have one).Last edited by Baila La Pinza; 04-06-2011 at 04:26 AM.
Reply:Thanks for the info y'all. I got started on the project this evening.  Got alot done before my phone went to ringing again so back to work I go.Miller BobcatHarris cutting outfitMiller spectrum 625 plasmaVariety of shopmade tools
Reply:Originally Posted by jbmprodsthe method i would use is on the hump side start in the center and heat in and ever widening circle like a spiral watching the metal as it moves to straighten until the desired effect is complete. then i would blow low pressure compressed air on it to cool it slowly following the same circle pattern.
Reply:Originally Posted by jw3This evening while heating the high side,instead of flattening out the hump grew.  I got called back in to work so I didn't see what happened when it cooled. Does this sound right?