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Thread: butt weld or flange weld

  1. #1

    Default butt weld or flange weld

    Hey Kevin im sure you have answered this sometime or another but i can't find the answer so i'm asking. which is better or preffered butt weld panels or flange the panels and then weld? Or does it matter what you are doing for example a show car or a daily driver or does it depend on what you are replacing like floor pans , quarter panels, etc. Any info will be greatly appreciated. thanks dslosjr

  2. #2
    Join Date
    Jul 2009


    On exterior sheet metal I usually butt weld... the end result is much easier to work with, requiring less filler. The benefit of a flange or overlap weld is that it's stronger, which comes in handy with floors, firewalls, and internal structural panels. On an exterior panel, IE- a quarter or door skin, you have a better chance of retaining the original crown and shape of the panel with butt welding.... since you dont have to distort it by making a flange. The exception to that is using a backing strip, about a half inch overlap on each side of the weld, and that way you essentially have a butt weld, with extra strength, without the destructive tendency of the pressed flange.... I use this method at the top of a sail-panel when replacing a quarter, which is also an ICAR mandated repair technique for late model panel replacement.

    Good luck!


  3. #3
    Join Date
    Sep 2009
    Central Illinois

    Default butt weld

    On the segment on TRUCKS where you were moving the wheel well forward on Project Rolling Thunder, your tips on cutting both panels at the same time and then butt welding them with an exact .040" gap was excellent. However, you didn't let us in on starting butt welds with the gaps. I have been practicing with my Eastwood 135 on a piece I took off of my 87 Formula that I am replacing but I keep blowing up the gaps with either huge globs of metal or ragged holes. What is your technique for starting to fill in these gaps? I am perplexed at how easy you make it look.
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  4. #4
    Join Date
    Jul 2009


    First thing.... THANK YOU!!!! for listening to me when I say over and over again to PRACTICE on a scrap panel... it really makes a difference. Secondly, really play with your heat settings... the slightest difference in settings can make a huge difference in how a gap is filled. Have you tried the copper backing techniques? Copper works well as a heat sink, and will help fill gaps, provided you can get a direct contact right behid or under your gap.. literally a backing strip-effect with Coper which wont get melted or fused in the weld. THIRD...... prep the edges of your two sections.... one big reason for undercut or blowing out a butt-weld is that there may be ragged edges on your metal that accellerate heat transfer. Look at it like a piece of paper... tear it in half, light it on fire, and the shredded edge will ignite MUCH FASTER than the pre-cut edge on the perimeter.. it's simple chemistry, and the air in between the paper fibers allows better ignition..... just like the ragged edge of the unprepped metal lets oxygen into the HAZ and accellerates the metal changing from solid to liquid- IE burning through faster.

    180 grit sand paper just to eliminate burrs on each edge of a butt joint is all it takes... and 180 wont change the profile of the edge much ,if at all.... just cleans it up. also, cleaning your weld are seconds before you weld is very important... I used to think this was just for aluminum and stainless... not correct... I've learned, mostly from Ryan Shand, that carbon steel also contaminates easily, and you benefit with BETTER WELDS if you wire brush the joint area right before throwing the coal to it.

    Third ( and a half) thing to try, is to create a smaller gap... it looks like you're ( in the picture) using a 1/8 inch blade to make your slices... thinner is sometimes easier, and you dont need to use as much heat to create your pool. once you've established a weld pool that bridges the panels,,, weld off of the cooled bridge.... NOT off the actual work piece... this stablizes your heat and cuts down on runaway heat into the workpiece.

    Hope this helps!!


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