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Thread: Stitch welding

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    Registered Member Gregs04.5's Avatar
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    Stitch welding

    Question on sheet metal welding. After tacking the patch in, do you "stitch weld" the entire seam, or is it ok to leave gaps?

  2. #2
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    Greg, here's what I do, and I think most.

    This is for mig welds mostly, though it applies to any welding equipment or procedure. Tack your panel in place. The tacks should be separated widely. Usually I tack one end, the center, and the other end first - for each weld seam/direction. Make sure that there is little or no gap, and as you make more tacks, that the gap doesn't change. If it does, grind the weld and break it, and do it again. If at all possible, avoid square corners. I.e., trim the new and old panels so that you have a radiused corner.

    Then come back and tack again halfway between the original tacks. Keep doing this, tacking halfway. Once you have tack welds fairly closely spaced (say 1"), it's time to grind them flat and planish the tack welds to make sure that patch is level with the original metal. Then you can resume tack (stitch) welding until you have a solid joint. Then you can dress the welds with a grinder and planish the welds.

    Robert (MP&C) has posted this procedure with photos. You may want to search his posts.

    You don't want to leave a gap, ever.

  3. #3
    Registered Member MP&C's Avatar
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    Greg, what are you welding in? Can you post up a picture?
    Robert



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    Registered Member rockytopper R.I.P 5-13-2017's Avatar
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    I did not show this in my qtr pnl patch thread and not to hi jack but it has relavance. I tacked my panel in place about 2 inch apart. I then ground all down almost to grade each tackweld per Robert teaching. I recall he said he then starts on one end and welds grinds and planishes each weld going one one direction. I welded each spot along the patch and then stopped a ground each weld. Then over lapped per Robert direction and just repeated until done. So I welded say 5 or 6 spots each pass and and then ground them down not just one, grind, & planish as I believe Robert teaches hope I'm making sense. I was unable to planish as planned during welding because of limit access so I got lazy should have made custom tool as Robert teaches but didn't. Latter found I could squeese my hand behind and planished after I already welded the entire panel. I used these eastwood clamps to secure patch. I fit my patch pretty tight along the entire edge of patch but I cut small indents in edge to allow for clamp thickness .05 or so gap. I used magnets to hold clamps in place to attach and remove once tacked. I'm pretty sure these gaps created most of the distortion issues I experienced even thou I did not planish as much as should due to limit acess. It just seem when my repeat process was welding the gaps it went south quick. Any input would be appreciated before my next one about to start.

    Last edited by rockytopper R.I.P 5-13-2017; 02-21-2016 at 07:21 AM.

  5. #5
    Registered Member Gregs04.5's Avatar
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    Quote Originally Posted by MP&C View Post
    Greg, what are you welding in? Can you post up a picture?
    I have not started welding yet, but I will need to weld in a patch piece in the rear of the trunk, and will also replace floor panels.
    I have a Miller 135 Mig, and plan to practice before touching the car this spring, so I'm looking for advice/ videos to help me out so I don't f**k it up.

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    Registered Member chevynut's Avatar
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    Just jump in and start practicing. Once you get going you'll get the hang of it.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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    what dose it mean when you say planish the weld

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    Registered Member chevynut's Avatar
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    Quote Originally Posted by 5557mad View Post
    what dose it mean when you say planish the weld
    Welding always causes the metal in the HAZ to shrink. Planishing with a hammer and dolly, using a hammer ON dolly technique stretches the metal back out reducing or eliminating the warpage caused by the shrinking.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  9. #9
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    thank you i understand that now. what do you do if you cant get a dolly behind the weld. just learning to run my welder

  10. #10
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 5557mad View Post
    what do you do if you cant get a dolly behind the weld.
    You do what you can to minimize warpage. That is cutting patches and putting weld seams in high crown areas or close to creases, rounding the corners, and keeping the heat down to minimize the HAZ.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

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