Help! Saggy table top

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Okay, after having worked almost 3 weeks on my cart, I made a crucial error I am using a 1/8" top for my table (due to weight considerations, it is a swingout table). I have read not to fully weld the top to the supporting frame because it might distort.  Well I made a series of tacks starting with the center support as shown - and the top distorted.  The top is sagged about a 1/8" or so towards the center of the worksurface.  I realize that it is going to be difficult to keep the top from warping, given it is only 1/8" thick, but I took a LOT of pains to make sure the supporting frame was dead-flat before I tacked the top. Is there some way to recover from this without starting from scratch? Attached Images
Reply:Heat draws. I have successfully pulled (drawn) a warp from pipe, frameworks and plate using a rosebud, but not understanding the explicit dynamics involved, it's not always successful. All I can tell you is to heat it up until it "draws" the warp out, and let it cool. If it doesn't go back to the original distortion, you were succesful. Don't heat it to the point that it is cherry red, watch it while you heat it and try to get it to "draw" past flat somewhat and let it cool on it's own. It's trial and error with this method, but I've had more success' than not. Good luck.Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize we cannot eat money.                                         -Cree Indian ProverbSA 200 LincolnVictor Torches
Reply:Pretty much1/8" will just be one hell of a mess trying to get it back to Flat with any Flame heating.Ed Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:Did you clamp the table top down before starting to tack it? Often times you can get rid of a gap by hitting the steel with a heavy hammer where u tacked it while its still hot. You will probly have to cut it apart, grind it up and start over.Nothing Ever Got Done By Quitting, Never Give Up.
Reply:I would suspect the tack caused your frame to bow. The tacks contracted.   I don't know what you used for frame material, however, I usually try to straighten stuff cold, first.  Make a straightener: a piece of metal that spans the warp.  Place blocks between it and the frame, then use c-clamps to reduce the bow by tightening them. Move the clamps and blocks to influence the placement and sharpness of the bend.  As with any bending do it slowly and small increments.  Check against a straight edge.If you decide to go with heat, as suggested.  Heat the bottom edge of  you frame then cool it with water.  as stated trial and error.  You can experiment with scrap.  Heat and edge watch the metal run away, then cool it and watch it come bend the opposite direction.  The contraction is more powerful then the expansion.Last edited by tapwelder; 05-18-2009 at 04:58 PM.
Reply:rosebud.. heat the other side..
Reply:Good suggestion by Doug. Try peening, even now that it is cool.  Got nothing to lose.
Reply:You could also add a couple more cross supports.This is a small table top I made for putting on top of saw horses before I made my bgger table. Attached ImagesEd Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:Only way to do it is to add a support in the middle, I assure you that if you try to heat it its just going to get worse.  It can be done but it takes some practice to get it right, and it seems like your pretty concerned with having this flat.IMO, 1/8 is to thin for a worksurface that needs to be flat, it will eventually sag anyways from normal use unless you have more support.  You ever plan on putting something heavy on there, maybe use a big hammer to adjust something? Should of gone with 1/4" me thinks.Have we all gone mad?
Reply:Try reheat your welds and take the chipping hammer to your welds and possibly try to see if more trusses can support any low sections.Take something you know is flat and run it along the top so you can see what is distorting and a better consideration may be to weld tabs underneith and bolt the top to the tabs(a number of different obtions, studs, flush heads etc.), you can still keep it to 1/8th.
Reply:Pay attention to where and how you place your tacks in the future. Distortion forces from cooling weld material will always be in effect. If you decide to cut it loose for any reason and want to save both parts, it's gonna be tough to get a grinder inside those square corners. We've all been through it in one form or another... Good luck! maniak
Reply:I think I'm gonna look upon it as a learning experience and live with the sag. I don't really have access to a torch to play around with thermal stress relief stuff. I used thin wall tubing (18 g) for the frame, and it most likely warped due to the welds contracting.  The strange thing is, it sags in the center where there is a support beam - it is also the first area I placed tacks ...Thanks for all the suggestions - I'm learning a bunch