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Hot Rods failed plug weld attempts

Discussion in 'The Hokey Ass Message Board' started by old_chevy, Jul 22, 2020.

  1. old_chevy
    Joined: May 28, 2012
    Posts: 69

    from USA

    I'm a newbie trying to plug weld on some scrap 18 gauge metal. I know to have clean metal and to degrease. Im using a mig and start in the middle of a 5/16 in whole. it takes me two circles and im still not completely filling the whole. So when I grind there is a lip from the hole when flush. is this expected? I think I'm failing to do this correctly.
  2. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,153

    Mr T body
    Alliance Vendor
    from SoCal

    I'm hardly an expert, but when I plug weld I start at the edge and swirl my way to the center. The center doesn't really hold anything, so making sure the perimeter has good penetration is important. Consider going to 3/8" as it's a bit easier to get into the edge with a slightly larger hole.
    May not be text book, but works for me.
    73RR, squirrel and Just Gary like this.
  3. X2
    Also try increasing your voltage & wire speed settings to get more molten metal into the hole.
    Bandit Billy likes this.
  4. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,460

    from Brooks Ky

    What size wire are you using? 18 gage is pretty thin. If you are using .030 wire, its a little iffy for something that thin. Might want to try some .023 wire. If you do, change the liner,tip,and drive rolls.

  5. two couped up
    Joined: Feb 22, 2006
    Posts: 65

    two couped up
    from pa.

    I start the weld on the edge of the hole and finish in the center.
    49ratfink and Just Gary like this.
  6. Blue One
    Joined: Feb 6, 2010
    Posts: 10,682

    Blue One
    from Alberta

    Mig is a fast freezing rather cold starting process.

    Sometimes if you try spot welding a small hole the hole is filled up before the metal at the bottom of the hole is hot enough to get any melting action and you end up with no fusion.

    The way to cure that is to set up the voltage hot enough that you will almost burn through the 18 gauge when you hit the trigger.

    I have the most success with spot welds with high voltage and the matching wire speed so that a spot weld is a short hot blast that melts into the base metal and quickly fills the hole flush or a little more.

    Set up some practice pieces on your welding table and you’ll find what works.
  7. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 6,884

    Bandit Billy

    ^^^Yep, hot! And back it up with a spoon or a brass drift. It will act as a heat sink and make the inside of the plug easy to finish. I welded up the spare tire hole in my running boards (almost an inch) in seconds after turning the end of a drift to fit snug in the hole and filling it from the outside in. It was red hot and flowed out nicely, very little grinding to finish. Of course running boards are a lot thicker than what you are working on but same basic idea.
    GordonC likes this.
  8. RJP
    Joined: Oct 5, 2005
    Posts: 1,657

    from PNW

    Hot, fast, and extend your wire about half an inch outside the nozzle. Do some test pieces.
  9. As Bandit Billy mentions, a brass backer from the opposite side works great. I’ve made a number of them from various sizes of round brass stock with a file handle and a piece of 1/4” brazed to the brass. You don’t want to try holding the brass by itself
  10. lostone
    Joined: Oct 13, 2013
    Posts: 1,369

    from kansas

    X3..... Hot, extended wire, almost a burn thru.

    Practice practice practice !! Once you get the hang of it, it's a piece of cake....
  11. old_chevy
    Joined: May 28, 2012
    Posts: 69

    from USA

    Thank you for the tips. I'm use .023 ESAB easy grind wire. All of the instruction videos I found online mention starting from the center. I'll try also from the hole edge. I have 4 heat settings on the Miller mig. I've been using the lowest setting at 1. I'll turn up the heat and try that also. Also will try with a backing plate of copper.

    So to confirm I should fill the hole completely in my plug weld? Right now I'm getting about 15% of the plug weld hole lip with no weld coverage.

    Does the metal on the back side of my plug weld need to be clean?
  12. jetnow1
    Joined: Jan 30, 2008
    Posts: 1,595

    from CT
    1. A-D Truckers

    all metal should be as clean as possible, both sides. I am no expert, but find for me that starting at the edge and working in works best. I also find that short, hot bursts get better penetration without burn thru.
  13. GordonC
    Joined: Mar 6, 2006
    Posts: 2,099


    Holes should be clean both sides if possible. Use a piece of copper or brass to back up the hole your welding. Inside the cover of your Miller mig should be a chart with settings for different thickness of material. A good place to start but adjust from there based on what your seeing/experincing. Have always started from the edge of smaller holes and worked into the middle of the hole I'm filling. Larger holes I use a plug and weld that in. My 47 Ford firewall had 73 holes in it and it was a great place to learn how to fill them!
  14. Paul
    Joined: Aug 29, 2002
    Posts: 15,028


    make sure the two pieces to be welded are firmly held together.
    And put the ground clamp on the piece behind.
  15. saltflats
    Joined: Aug 14, 2007
    Posts: 10,316

    from Missouri

    Guess I do it different, I start in the middle and hook out then work back to the meddle. I also run my tip up in the nozzle.
    Last edited: Jul 22, 2020
  16. ricky_tbird
    Joined: Aug 20, 2015
    Posts: 28


    I am with you saltflats. Getting a hot puddle in the center seems to get the edge of the top piece of metal glowing and then trace the hole with the nozzle to fuse everything together. Yes to clamping because it sucks when then weld lifts the top and you get a gap.
    Blue One likes this.
  17. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,544


  18. gene-koning
    Joined: Oct 28, 2016
    Posts: 2,033


    Ut oh. For 30 years I did all my mig welding with .035 wire, including the plug welds on the 20 gauge sheet metal. Clamp the clean metal together, turn up the heat, start on one edge, fill the hole in a circular motion, move fast. Makes nice flat welds that require very little touching up with a sander. A good plug weld will rip the metal apart before the weld fails. Gene
    iwanaflattie and thintin like this.
  19. 66gmc
    Joined: Dec 4, 2005
    Posts: 558


    I was taught to start in the center and go out, clamp it tight and crank the heat. Get in an get out as fast as possible. The entire edge has to be welded, any missed spots are just a place for rust to start. After a lot of practice it just becomes second nature and if you get your welder dialed right in you can end up with something that resembles a factory spotweld after a little cleanup with a grinder.
  20. saltflats
    Joined: Aug 14, 2007
    Posts: 10,316

    from Missouri

    This is the setting I use on this machine with .023 wire.
    Last edited: Jul 23, 2020
  21. b-body-bob
    Joined: Apr 23, 2011
    Posts: 455


    Me too (not that long). I never had any luck with thinner wire. The copper spoon above can be bought at Harbor freight. I ordered a couple of fancier hands-free backers made by VIM and a clamp with a copper backer from somewhere.

    Last edited: Jul 24, 2020
    Gasser 57 likes this.
  22. bobscogin
    Joined: Feb 8, 2007
    Posts: 1,761


    Yup, that's the trick.

  23. old_chevy
    Joined: May 28, 2012
    Posts: 69

    from USA

    Thank you! I have a Miller much like yours. I tried the same settings as you shown with .023 wire. I'm finding that the puddle is laying flat... it fills the hole more easily and quickly at 3-50. I had been using setting 1-50 and the puddle did not go down flat and fill the hole. I'm also using the copper backing with 3-50. A much smaller heat ring is produced with the copper backing. I also found that I need to hammer and dolly to bring the metals together. Clamping force alone does not always close any gaps and im left with a lip in the plug weld.

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