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What's The Right Way To Mig Weld A Joint

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  • What's The Right Way To Mig Weld A Joint

    Hi Guys

    I'm a newbie to mig welding. However, I've done elec./tig for some 16yrs. But unfortunatly, I never needed to mig weld. I bought a Millermatic135.
    So here I am.

    I'm about to take the challenge an restore my ' 66 Mustang Convert.

    Here's what I've been reading about and is this the right way to
    mig weld a joint.

    1st. Clean the metal and spray with Weld-thru coating.
    2nd. Tac at different places before I lay-down a continous bead.
    3rd. After the joint is sealed spray with an rust converter.
    4th. Cover entire weld with seam sealer.
    5th. Spray with an primer/ etching primer.

    Is that the steps I should do as I prepare to weld a joint together?

    If I missed anything please don't hesitate to help me out and direct me
    to the correct steps.

    Thank you
    GOD Bless


  • #2
    I personally wouldn't bother with the weld through covering (you wouldn't prep a tig joint then spray it in paint would you?) it's just a potential contaminant in your weld. Tack weld everything as you said but i would go for a series of small 'stitch' welds maybe an inch or so long and lay them at intervals coming back to 'fill in' the gaps. This should reduce the risk of burning a hole in the joint.

    I'm not really ann expert in body repair so maybe somebody from the motorsport board may be able to help you some more.



    • #3
      Hi Russ

      The weld-thru spray prevents the area from rusting-up after I finish mig welding the 18ga. sheet metal.

      Its a great way to stop rust after welding.
      And the seam sealer is a protection over the weld when its completed.

      Other than that Thank you for you input.

      GOD Bless



      • #4
        I would also post this on the Motorsports board. I am almost 100% sure from my limited knowledge that you do not want to make continuous beads on sheet metal,it will warp. Like the previous post said,make a small weld(an inch may be too much),skip several inches,make another one,etc,then keep adding to them from the beginning. Then you get to practice your grinding skills. Good luck.


        • #5
          I personally dont mig weld any body work if I dont have to, I know many professionals that prefer TIG of OA welding it as well. The weld-through primers are more of a marketing ploy then anything. Its a zinc rich paint...but the backside of your weld will still corrode where the heat vaporized the paint off. Tack often, weld in segments followed by cooling the panel ( no you wont harden or shrink it ), if you can get to both sides of the panel so much the better as you can planish it out. best corrosion packages are as follows:

          Option 1 (best)

          Bare Metal-Zinc Chromate primer-Enamel ( no hardener ) or Laquer topcoat

          Option 2 (ok)

          Bare Metal-Epoxy primer with chromates-Urethane or Enamel (with hardener)topcoat.

          Option 3 (better)
          Bare Metal-Phosphate treatment-chromate free epoxy primer-Urethane or Enamel (with hardener) topcoat

          Option 1 gives better performance due to the non hardened topcoat pore structure allowing oxygen to get to the metals in the primer, and allowing them to be the sacrifical element.

          The Modern paint finishes are designed for application over a phosphated steel substrate which takes the place of zinc ( this was done for enviro and cost reasons, not performance) and doesnt require the breathing ability of the topcoat. Therefore using them over the zinc primers doesnt give as good of results.

          Hope this helps and doesnt add to the confusion

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          • #6
            Hey Guy

            Thank you for your input.
            I will take what you said un consideration.

            Thanks again
            GOD BLESS



            • #7
              i have to agree with the guys on the 1" only then move, or atleast let it cool a sec. i just helped put in some floorboards and did it in about 1" tacks. the metal will store up heat and you will blow threw if you go much more than 1" at a time. unlike in TIG you cant back off on the foot controle to make up for the heat you are adding. it would also most likely worp out big time if you did manage to get a full bead weld.
              i was working on 20 gage but whatever yo will be using i would do a few practise welds to get the hang of it. you should find it prity simple after TIG. i have had a MM135 for over 6 years now and its a great lil welder. i used it and a MM210 on the floor pans. the MM135 with some .025 wire and C-25 woule be best but i had strait Co2 in mine (MM135) at the time and C-25 in the MM210. so eather will get the job done. after running a few beads you will be ready to go to it, and should realy like the MM135.
              be shore to post up some pic's of the progress.
              thanks for the help
              hope i helped
              feel free to shoot me an e-mail direct i have time to chat. [email protected]
              summer is here, plant a tree. if you don't have space or time to plant one sponsor some one else to plant one for you. a tree is an investment in our planet, help it out.


              • #8
                when I was told how to weld body metal in my class last year I'm not sure if im right but my teacher told me one person can weld and behind him (or her) comes someone with a wet rag or what ever you want to use towel etc. and just cools the weld right down and prevents the warpage. I'm sure you would still have to stop and let the area cool down but it would be less time on stopping with the water trick and I'm sure you could go for more then 1".

                I hope this helps
                Thanks for reading I hope my post helped



                • #9
                  Originally posted by SCHOONER View Post
                  Hi Russ

                  The weld-thru spray prevents the area from rusting-up after I finish mig welding the 18ga. sheet metal.

                  Its a great way to stop rust after welding.
                  And the seam sealer is a protection over the weld when its completed.

                  Other than that Thank you for you input.

                  GOD Bless


                  If your gas pressure is right and the angle your welding at is correct, you shouldn't have to worry about rust/oxidation. Thats what the gases are for. I agree with the guy that mentioned contamination from weld through covering. A good clean metal is all you REALLY need. I've seen plenty of tubs done on pickup truck beds.

                  This is after the bed was cleaned, ground to bare metal where needed, tacked, seam sealed, then primed. the trucks axel can have full motion to lay the body on the ground.

                  The bed of the truck is going in for rhino liner right now.


                  • #10
                    I have to side with Brightspark on the weldthru, I have mig welded more VW sheetmetal than I care to think about. Just get it very clean and spot it togeather then weld between the spots about 3/4-1" at a time moving around and waiting a bit on each weld for cool down. if you are doing butt welds and can get behind the seam, use a copper peice for backup. I wouldn't use any anti-splatter either, just use seam sealer on the back side and primer the front after grinding it smooth and using plastic or lead filler to get the imperfections. If you are doing patch's then a hand/air flanging tool works great and is cheap to buy, and will make for a stronger joint. JMHO
                    Regards, George

                    Hobart Handler 210 w/DP3035 - Great 240V small Mig
                    Hobart Handler 140 - Great 120V Mig
                    Hobart Handler EZ125 - IMO the best 120V Flux Core only machine

                    Miller Dynasty 200DX with cooler of my design, works for me
                    Miller Spectrum 375 - Nice Cutter