7 ft. butt weld

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Hello,I am constructing a larger flat in sheet steel (3/16 or 5mm) from three laser-cut parts by means of butt welds. Weld lengths are approximately 7 feet long. Dimensions of the larger flat are 12x7 ft (4000x2300mm).I would like to get some pointers on how to keep the whole thing straight all the way through the welding process, or how to proceed so that parts straighten out after welding.Thanks,maurits
Reply:first off what method of welding are we doing?tack the middle..then the ends..halfway between the middle and the ends another tack..then go with  1" to 2" welds from the middle out..keep alternating sides to keep the heat build up in one place to a minimum..you have alot of welding to do.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:first off what method of welding are we doing?
Reply:Here's a 4 foot weld I did with  oxy-acetylene.  It is a corner of 14g steel.  It is backed with 1/8 inch angle.  The sheet was tacked to the angle from the inside with a stick welder and the outer corner was tacked approx. every 2 inches stick, also.  I back stitched o/a welded going down.  I welded between tacks going up to the previous tack progressing from top to bottom of cabinet.Oh yeah, I did keep a move a wet rag along side of the weld.The ripple seen in the finished photo came from arc welding the shelving inside. Attached ImagesLast edited by tapwelder; 09-04-2006 at 01:49 PM.
Reply:Originally Posted by mauritsmig 500A watercooled, wire SGjust 5 tacks total on 7 ft. Isn't that being a little stingy?I'm planning to V-groove the sides on the front side, because it gives a nicer weld visually. If I were to do that I assume that shrinkage would be more of an issue. You think that is true? And if so, how do I compensate for that. Pinning it down the parts with a couple of I-beams?Is it advisable in this case to use backing ceramics?  And it's just a small part of the whole project.--maurits
Reply:Welding from one side is going to increase your problems.Your plate is going to shrink transversely across the weld bead.  If that transverse shrinkage is more on one side than the other then you will not get a flat joint.  If you have lifting equipment consider welding one side for a third then turning it over to weld the other side and back again to finish.If you weld from one side you could prebend the assembly. You could also tack weld on strong backs across the joint every foot with mouseholes over the joint.  Vee prep and flat welds mimimize distortion.The other shrinkage you will have to contend with is longitudinal.  The weld will try to shorten up lengthwise lifting the seam into a bow.  Skip welding and back stepping is about all you can do.  If this sheet is going down onto a frame maybe that should be done before welding up the seam.  Sometimes people weld continuously when it is not required.  Ask yourself if this is the case.
Reply:@lotechmanFlipping back and forth while finishing the weld makes sense. I have an overhead crane at my disposal so I might try that.Mouseholes over the joint? I don't know what you mean by that. Could you elaborate a little bit?The sheet is just going to be skip welded onto a vertical frame. Frame is not stiff enough for the plate to be welded up against.@zapsterWhat do you mean by "an aluminum bar right down the middle where the weld is going and pin it down about a foot in from the sides.."Thanks both for your thoughts
Reply:Originally Posted by maurits@zapsterWhat do you mean by "an aluminum bar right down the middle where the weld is going and pin it down about a foot in from the sides.."
Reply:[QUOTE=maurits]@lotechmanFlipping back and forth while finishing the weld makes sense. I have an overhead crane at my disposal so I might try that.Mouseholes over the joint? I don't know what you mean by that. Could you elaborate a little bit?The sheet is just going to be skip welded onto a vertical frame. Frame is not stiff enough for the plate to be welded up against.A strongback would be a piece of flat bar say 14 by 3 and about a foot long.  You would torch a half circle about an inch round in the middle of one edge.  Tack weld ten of these across the joint standing up.  The half circle cut makes a mouse hole you can weld through while the strongback holds the plate flat.   There is no guarantee in your case if you are welding on one side only that when you snap the strongbacks off that the plate does not spring.  If you have a crane then backstep weld and skip over the seven feet for about a third then turn the sheet over and weld the other side.  Keep monitoring the pull on the plate and weld on the side that need pulling.  Like I said before it is a lot better if you don't have to have a continuous seal weld full length.
Reply:Originally Posted by ZTFabPlace the aluminum round bar underneath the center of the joint to be welded (parallel to it) and clamp the pieces of plate about 1ft in from each end to "pre-bend". This will counter-act the movement caused by welding.
Reply:Originally Posted by zapster thanks.. ...zap!
Reply:Why does it have to be welded 100% or did I miss that?Weldtek
Reply:Originally Posted by WeldtekWhy does it have to be welded 100% or did I miss that?
Reply:[QUOTE=zapster]check post "a"???? Duh, I'm still missing it. What's a larger flat?Weldtek
Reply:i think he wants a huge piece of 3/16 made out of the 3 that are on the floorlooks good on paper......zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Ditto.Weldtek