How do I stop undercutting?

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I'm MIG welding steel 1.5" angle iron to 1.5" square tube. (All 1/8" thickness) I have a small autoarc 130, 1/8 - 3/16" is the limits of the machine so I am at max voltage, wire speed 20/100.Not every time but once and a while it undercuts at the edges of the top of the bed, not so much the bottom edge. I tried dropping the voltage and go sputtering so i turned it back up to max.
Reply:A lot of times you just have to change the gun angle.Don’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:Watch the puddle fill in. Gun angle could be wrong. I would also say your running it too hot, but you said you already tried to decrease volts/wire. Plus its a 110 machine on 1/8, so your just about maxed out, so I wouldn't assume its too hot.Ya gotta spend money to make money!
Reply:Trying to watch the puddle and weld it to begin with is difficult for me with this one because it's a corner with angle iron against square tube at a 90* angle. So it's a tight short run and the gun basically blocks seeing the puddle since I'm working from the inside edge of the corner to the outside pulling the gun.
Reply:You can control undercut a few different ways. You can turn your voltage/amperage down. You can change your gun/rod angle and point it at the undercut. You can slow down and fill the undercut in with weld metal as you see the undercut develop.  Try different things. You will get it.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:How do you stop undercutting?The same way you get to Carnegie Hall.  Practice.  The three main causes of undercut are excessive arc length, travel speed too fast, and improper electrode angle.Too low voltage causes the wire to stub into the workpiece (pushes the gun/torch back).  Too high voltage causes the arc to be unstable (excess spatter).IIRC, you are/were doing a lap joint of the angle iron onto the square tube, yes?  If so, your 'undercut' on the edge of the angle iron is more like an "underfill", as the arc melted away the top edge of the angle iron and you didn't get enough wire filler in there to correctly/properly fill in the weld bead.  Mostly that's too fast of a travel speed or slightly wavering on your travel position/direction, possibly because you can't or aren't seeing the "puddle" (not just the bright light of the arc, but the actual puddle of the molten steel).Practice, practice, practice.  The best laid schemes ... Gang oft agley ...
Reply:Originally Posted by MoonRiseHow do you stop undercutting?The same way you get to Carnegie Hall.  Practice.  The three main causes of undercut are excessive arc length, travel speed too fast, and improper electrode angle.Too low voltage causes the wire to stub into the workpiece (pushes the gun/torch back).  Too high voltage causes the arc to be unstable (excess spatter).IIRC, you are/were doing a lap joint of the angle iron onto the square tube, yes?  If so, your 'undercut' on the edge of the angle iron is more like an "underfill", as the arc melted away the top edge of the angle iron and you didn't get enough wire filler in there to correctly/properly fill in the weld bead.  Mostly that's too fast of a travel speed or slightly wavering on your travel position/direction, possibly because you can't or aren't seeing the "puddle" (not just the bright light of the arc, but the actual puddle of the molten steel).Practice, practice, practice.
Reply:For the sake of not making a new thread,Why is it sometimes when I go to start a weld, it just goes insane and spatters everywhere and doesn't "catch" and form a puddle. I move over 1mm and start again and no problems? Is it from contamination?