What is the trick/problem when welding inside corners?

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Hi,I've been building boat trailer parts. It's all fairly heavy stuff, 5 inch channel 5/16 gauge or so. When I say outside, basically I mean if you put a piece of channel on top of something making a 90 degree angle - if you were going all the way around it with a bead, you weld 3 edges "outside" then 3 edges "inside". Outside corners I seem to have no problems - or at least I can control what I'm doing, making a flat or convex weld, everything lays in OK.. I can slow the speed way down and make a big wide bead or go slower and make a smaller one, molten metal lays down kinda as expected..Same settings & rods and I move to an inside corner (where it's a real pain to grind out too) and everything goes to hell - undercut, splatter, sticking, blobs.. What makes this go south? What might I try to make things go smoother?Forget the sizes (I think everything I buy is 1/8, could be 5/32) but am using 7014 and 6013 rods (usually they both feel kinda the same to me and I'm using the 7014 on the outside, but alternated attempting to find something that worked better)... DC positive, was using ~120 amps on the outside but upon undercut stepped all the way down to less than 80 amps attempting to correct the problem, at which point kept sticking rods and gave up on going down. Try DC negative? AC? Change my angle? There must be something fundamental I'm doing wrong.Thanks in advance!Jon
Reply:Weld from the outside edge to the inside of the corner, eliminates the arc blow.
Reply:Inside corners can be a bit tricky. Sometimes I'll weld into the corner from one side, then stop. Then I'll weld into the corner from the other side ensuring I melt into the end of the first weld into the corner, then stop. When welding structural steel I'll sometimes encounter arc blow when welding inside corners. You have to find a way to do it that works for you. You may have to try a few different techniques to find something that works for youJasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Try AC if you have it available on your welder.On DC wrap the ground cable around the steel, if not effective wrap it the other way.Read this:       http://www.lincolnelectric.com/en-us...ow-detail.aspx"The reason we are here is that we are not all there"SA 200Idealarc TM 300 300MM 200MM 25130a SpoolgunPrecision Tig 375Invertec V350 ProSC-32 CS 12 Wire FeederOxweld/Purox O/AArcAirHypertherm Powermax 85LN25
Reply:Thanks guys! Yes it's an AC/DC, miller thunderbolt.
Reply:Forget ac and dc neg, he never indicated an arc blow problem. One issue may be the temp. If you just welded the outside, the the piece is a lot hotter than when you started. Let it cool off first. You can also use a smaller rod and lower your amp input. Also, i haven't in recent memory use 6013 or 7014, nor have I found a reason to. 7018 works grand for that, and is fairly easy to manipulate, you may try that. As far as the undercut, you have too much heat, and not enough fill time. So turn the amps down, use a smaller rod, and spend more time on the side you have undercut.The inside of a channel can be problematic to make in one pass because when you start welding on the flange you are pushing the electrode, then you are dragging it along the web, and dragging along the other flange. Try bending the rod to improve the angle on your first flange weld. Otherwise, weld the flanges first, grind your starts, then weld the web.
Reply:Well I tried AC (maybe should've tried DC neg too) and that was totally night and day. Still a little tricky because of the funny angles and the fact that being a stick I want to go around it in one pass to avoid needing to clean again. Actually, given the way I welded one side (good bevel and areas with poor fit that I basically filled), probably wasn't any reason to weld the other at all - but this is the 2nd time I've fought with the same issue so it's good to learn something that works.Will try a 7018 on the next pieces. Will be welding some 2 inch X 3/16 channel to thicker steel - what size do you figure I should go with?I'm not sure why I ended up with the 6013 and 7014. With this machine I started off with a bunch of 6011's and ran them for awhile, then last project wanted something more appropriate for new clean metal, and that would be easier to use, so got those. With a poor fit I've been using the 6013, then on subsequent welds over the same joint the 7014, and/or the 7014 with good fit up. Maybe this is stupid, I am admittedly a beginner. Thanks,Jon
Reply:For the materials you are welding I would use 3/32" 7018 on 80-85amps DC reverse polarity (electrode +). You'll also want to weld uphill with the 7018. Get a wire wheel on an angle grinder to make flux clean-up quicker and easier.In the field: '06 Ram 3500/Miller PP350    '14 F-350/Lincoln Classic 300DIn the shop: MM252, Hypertherm PM-85, White face MM200
Reply:Inside of two faces is not so bad.Where you have three faces that create an inside corner, it gets worse.Three sided inside corners act like slag traps, and DC will not behave well with arc-blow. AC counters the magnetic force that creates arc-blow with DC, but you still have a slag trap. Cleaning in between beads is real important, because fixing a screw up inside there is miserable. Somebody might have said already to work from the outside in, that might help.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:Shouldn't be getting arc blow with 1/8" rods but weld the inside flanges first.
Reply:Thanks for that guys - haven't gotten back to it but going to go at the next round with the 7018's and see how it changes things. Will try the wire wheel setup too - got one on a drill now that I use for the same purpose.