MIG welding poorly fit joints?

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Hello All....What do you guys do when you have to MIG weld poorly fitting joints?  For example, welding 90 degree joints using 2 x 2 1/8 angle that has been "notched" to make a flush fit.  Problem lies with the fit has been poorly cut, or there is a larger than you would like gap in your joint fitting.  Say the gap is 1/2, or greater.Should I try some type of patch on the backside and try and fill the gap from the opposite side?Any info is greatly appreciated.  Thank you.MetalBob
Reply:You could build the gap up with weld until you get a complete fill.  Whats it on?  Is it critical like a trailer or something that could hurt someone?Various GrindersVictor Journeyman torch200cf Acet. 250cf oxygenLincoln 175 plus/alpha2 gunLincoln v205t tigLincoln 350mpEsab 650 plasmaWhen you can get up in the morning, Its a good day.Live each day like its your last.
Reply:Fill it with a patch piece of metal.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Thanks guys for advice.  Keep it coming if anyone has more...Doolittle - no, it is NOT on anything that would hurt anyone.  Mainly a hypothetical question, but I have run into this.  Just wondering how you guys handle it.  Thx for responding.MetalBob
Reply:1/2" is a pretty nasty gap to try and fill, let alone try and make it look nice, and be something you want your name on. Is this something you could fish plate? either on the bottom as you suggested, or the top.
Reply:I'd at least try to fill part of it with a sliver. If it wasn't gonna happen, then I would build it up spot by spot, making some passes to get close. Then, when I could bridge the smaller gap I had finally created, I would lock it up in several spots before just filling it in. I would also say the best thing to do in that case is to keep the grinder around, and clean up the excess that you don't need. You will want to fill the void, not build mt. Everest out of filler wire.
Reply:With a 1/2" gap I would be temped to just replace the peice with one that fits better. However if for some reason you're forced to use it, I would build up each side of the joint untill they meet, if it's structural I would also plate it on one side, if not you'll probably be fine with just using a mound of weld.
Reply:Originally Posted by maxyedorWith a 1/2" gap I would be temped to just replace the peice with one that fits better. However if for some reason you're forced to use it, I would build up each side of the joint untill they meet, if it's structural I would also plate it on one side, if not you'll probably be fine with just using a mound of weld.
Reply:Many welders have a heavy copper bar in their tool box.  The copper is clamped across the bottom of the gap to support the molten metal.  Heavy copper bar is hard to find.
Reply:Great feedback guys.  Thank you.Lotech - pardon my ignorance, does the filler wire not weld to the copper plate?MetalBob
Reply:Other options: Structural: put on a backer and call it a backed full pen weld. Maybe a 1/8 or 3/32 (10 or 12 guage) slab. Tack it in, then fill the gap, burning into the backer. Finish with filletsover the backer edges to reduce stress risers. Non structural: a couple pieces of angle, one on each side, filletted to each part.Structural: Use a hunk of angle for th backer. Tack in place, fill the gap, then  put the angle on the other side (th side you filled from) and fillet both angles in.For something like channel or wide flange, where the flange clearance is cut back too far but the web is a proper fit, a backer is quite common, with the weld metal just being poured in to fill the gap.If the gap is the right size, slug it with a hunk of square stock turned so the corners stick out, giving two 45 degree vee preps on either side of the part, perfect for full penetration. By the way, an aluminum bar will work almost as well as a copper bar. Need to go a bit easier due to the lower melting point of Al. If you can grind the back side to remove contamination (or it doesn't matter) a graphite block will do in a pinch (like a large motor brush, for example)
Reply:Just fill it in. I do it all the time ( damn fitters). Make sure you chip after each pass. Also do a couple of passes and walk away. If you keep at it your metal will be to hot and you will cut through what foundation is there. Is this vertical or flat?- MattBMP Barge Marine Products "Welder"Mig, Stick, Air Arc, Submerge, & Torch
Reply:Originally Posted by jamlitWell said. I would do the same, but I would also do some major grinding to make it look good rather than a mound of weld.
Reply:Originally Posted by MetalBobGreat feedback guys.  Thank you.Lotech - pardon my ignorance, does the filler wire not weld to the copper plate?
Reply:Originally Posted by lotechmanCopper is best for backing because it will take more heat.  You run you weld against the steel edge and let the puddle roll onto the copper.  Aluminum or brass can be used but too much heat will casue problems.  Filling big gaps with pieces of metal goes way back.    During WW2 they paid welders by the poundage of electrode they consumed by tallying the amount taken out of the toolroom.  The waters around the dock were filled rod thrown into the water.  I had a boss who told me that as a young guy he got chewed out for being so slow on his welding until he started to chuck rod also.   The next tactic was to pay welders in shipyard by the length of welds completed.  They quickly learned that they could do more welds by dropping a 1/4 inch round bar into the joint and covering it over with a bead.  Some Liberty ships broke up in the North Atlantic for mysterious reasons.   Eventually shipyards realized that you got quality welds by paying an hourly rate and having regular weld inspections.  Filling gaps is not a quality weld but we all do it on occasion.  Just don't call that kind of weld a good weld.
Reply:1/2" gap on a weldment like that?  Sorry..Ain't no way..Do it over again.....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:Originally Posted by maxyedorI kind of assumed that this would be a joint one either didn't care about the appearance of, or would not be seen. If somebody could see it I would tell the guy responsible for fitting the joint to find a new job and I'd re-do it so that it fit nicly and could be welded in one pass. All that time spent building up the weld, then grinding it to look good is a huge waste of time and money. Then again I try and at least make all my joints perfect.
Reply:Unfortunately, in the real world, you end up with poor fitup and need to deal with it. A lot of the time, the monetary cost or time to remake a piece is a LOT greater than the time to fill the gap.
Reply:Originally Posted by jamlitSorry if I bothered you in quoting you before.
Reply:I use copper.If I Can't Weld It!-----It Can't Be Welded!
Reply:I had to play that game with a loader cutting edge, only with 7018.  I just ran bead after bead till it was the way I wanted it. The bucket was thrashed and the customer ordered a weld on edge. I cut the bucket square, but it was ugly. It wasn't an open root so it wasn't that bad just took a little time. Everything is fine, as the machine is working with no problems. As far as GMAW on structual always ask the Engineer(do you take the money or drive the train?) what is acceptable. Poor fit up is just lazyness and is a pain in our aressses.Disclaimer; "I am just an a$$hole welder, don't take it personally ."