Critique a newbie's welds...

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So, I've been learning to MIG weld.  I've been O/A welding for a few years, but recently started on a MIG.  I'm using a Hobart Mig-Man wired 220v with a bottle of 75/25 set at about 20cfm.  I THINK I'm using .035 wire, but I'd have to check when I get home to be sure.  I've got the heat turned all the way up and the wire speed set to where I get a nice sizzle per the MIG welding video I have and the sound that's made when every person I know that's a good welder makes.  This is a 4' piece of 1/2" square tube (prolly .125" wall) that I've been cutting a few inches off and welding back on, then attempting to break in my bench vice.  This is the latest one I've done and I think it's correct, but I'll let those of you who know what you're doing be the judge of that.The Weld.The Break.So, how'd I do?
Reply:Are you overlapping tack welds? or running a continuous stringer?I think contiuous beads on flat joints showcase a weld better and are easier to diagnose than those on small joints like you have above.Keep the pics comming.
Reply:For now, just tacks.  I'm really shooting for proper penetration more than anything.  I don't do it for a living, so I'm not worried about speed...
Reply:PS - what's a stringer?  Newbie here...
Reply:Originally Posted by timhypoPS - what's a stringer?  Newbie here...
Reply:Well, it looks like it broke in the base metal, not the weld, so that's a good thing.Like Zap says, if there's a crater, it will act as a stress riser in the initiation and propagation of a crack.  Pesonally, on this particular weld, I'd be more concerned with the sharp transition and lack of penetration (LOP) between the widely spaced spot welds.  These are a major stress riser.  If you want to use this overlapping spot weld technique, you should try to overlap them more so they form more of a smooth continuous bead.One thing to be aware of is that MIG allways gets less penetration at the weld start because the arc takes some time to get established, and so the first metal deposited is layed in cold.  So each of your spot welds would be colder/less penetration than a continuous weld made with the same settings.Thanks for the pics, let's see some more, maybe on a larger piece/longer weld.Stringer, a single weld pass, generally done with no weave at all, or very minimal oscillation, so that it remains rather narrow, as opposed to a weld that is clearly weaved from side to side.
Reply:Lets see some of your o/a welds!!!!
Reply:I never thought about the affects of the cold-start nature of MIG welding on the structural integrity of my welds.  I guess that's why when one of the old guys in our car club did the welding on our dragster frame, he did so much at a time.  How do you avoid burning up the edges with a MIG when you get there?  Gradually reduce arc length?When I get home, I'll dig up and post the pics of the O/A stuff I've done for practice.  I got the O/A to eventually do the time-honored technique of hammer-welding to do true metal repairs on our old cars, honestly I'm much better at gas welding than MIG, but I'll get there.  I know a '58 Olds isn't worth much, but that's not really the point, I'm just trying to learn this stuff.  Right now, I'm working on shaving the handles/locks on some Datsun 240z doors that I have just for kicks.  I'm using the MIG for that, though tonight I should have the right adaptors to hook up my Meco Midget and then I should be able to do really nice O/A work.  At least, really nice for me, I'm sure you pro-welders make mine look like crap any day of the week...
Reply:Also, what would cause the hole in the middle of my weld?  Metal not clean enough?
Reply:Originally Posted by timhypoAlso, what would cause the hole in the middle of my weld?  Metal not clean enough?
Reply:Originally Posted by zapsterIt happens when you stop the weld..You should tap the trigger twice after the inital tack..Build a small hill..Don't leave a crater..
Reply:I'll try that tonight, it makes sense, fill the hole while it's still red and before it fully forms...