plug weld-confused

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I plug welded a piece of 16 gauge to the tail pan(18 ga.) on my '39 Ford two door sedan for a deck lid striker support.  I have a Lincoln 175 amp mig.  I used the same heat that I usually do when welding 16 & 18 gauge, C & 5.  It didn't stick.  I drilled 1/4 " holes.   I've done a lot of welding on this car and haven't had this problem before.  Should the holes be bigger?  I'm stumped.  Thanks in advance, Rod
Reply:i hold it long enough till right before you think its going to blow a hole threw then let off the trigger other wise your just tacking it.
Reply:What puty72 said.  May need to up the heat a little above what you normally use for welding this material.  The key is to get sufficient heat in fast and enough filler to prevent blow thru.OR . . .. . . you can do it the way the old Miller spot weld feature works and set the voltage to the highest setting so it burns thru the top piece (thinner of the two if different) with no holes into the lower and WFS set to assure sufficient filler is added to prevent blow thru.  You only need to hold the trigger for a second +/- and the Miller spot control makes it easy to get repeatable results.  The Miller spot nozzles make it easy to hold the proper stand-off from the material as well.  Tweco makes spot nozzles for some of their guns and others may too.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:Quarter inch hole is on the small side. Go to a 5-16 hole and you should have better luck. I use a heat setting similar to the combined thickness.Miller xmt304,  Miller S22 p12, Miier Maxstar SD, Miller 252 w 30A, Miller super32p12, Lincoln Ranger 9, Thermal Arc 181I with spoolgun, Hypertherm 10000 ,Smith torches. Esab 161lts miniarc.
Reply:Seems like I've plug welded with a MIG welder about a million holes. One key is to make sure that the wire first touches on the lower (backing) piece. Don't move for a second until the arc burns and you get good penetration in the back piece. Then start a circular motion and continue until the hole is completely filled and rounded nicely on top. I've always thought about keeping a ball peen hammer next to me and peening the weld while it cools, which should keep it from "sucking in" in the middle as the metal freezes.I have gotten away with 1/4" holes lots of times but like the man says 5/16" is better.metalmagpie
Reply:Also, since we're talking old car sheet metal, make sure the metal is ground till shiny, not just wire-brushed.A few weldersA lot of hammersA whole lot of C-clamps
Reply:I do it exactly like the magpie does.