Progress Thread Welding Nightmare

Discussion in '1965 - 1973 Classic Mustangs -General/Talk-' started by 65-Fstbk, May 15, 2014.


  1. 65-Fstbk

    65-Fstbk Member

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    View attachment 90548
    Ok so I'm tacking along the butt weld seam for the new quarter. Nice beads, everything going well. I keep moving around and waiting etc. No problem. The problem for me always seems to be when I start grinding the welds down as I'll end up with a small ridge/lip on the seam where if I grind it it seems to make the metal too thin. Then when I try to fill pin holes I end up with blowthrough and from there it's a slippery slope such as......filling holes with weld bead, welding from the inside and occasionally a small patch. The seam then ends up being more wavy than I would like (too much heat I guess although I don't go crazy with the welds) but when I hammer and dolly to try and correct sometimes a seam will appear in the metal which tells me it's too thin and I end up having to patch again; round and round we go.

    Anyway the end result isn't perfect but it's going to need some filler so I'm looking for any advice you may have. Should I call it a day, quit while I'm ahead and let the glass reinforced filler do it's thing or continue to try and hammer and dolley??

    In the 'patched' pic I'm basically afraid to grind any more as it just seems to get me nowhere. I'm thinking....'know when to quit' may be a good approach and that filler will take care of the valleys etc. What are your thoughts?

    Thanks in advance. resize quarter.jpg
    photo(1).JPG
    Last edited: May 15, 2014
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  2. horse sence

    horse sence Please don't call me Mom SN Certified Technician

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    Cool your tacks as soon as you make them ,it a pain in the butt but it will keep the warping down to a minimum . I use a air nozzle to cool the welds ,you can use a wet rag but it causes the metal to to rust and will temper the weld. Cool after each tack and stitch weld all the panels ,that is a tack after a tack until finished . A continuos weld will cause major warping . I use a 90* air grinder ,like a die grinder to grind the welds with a 36 grit wheel .Do not try to grind the welds all the way down at once .You should grind in long areas at a time to keep the welds cool, grinding will cause warping same as welding .Your panel joint reappearing is probably do to not enough penetration of the welds ,you should see a blister on the back side of the panel after each tack. No blister is to cold of a weld.
    A copper bar behind the panel you are welding will help fill in holes ,welds will not stick to the copper .A flattened piece of copper pipe will work fine.
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  3. 65-Fstbk

    65-Fstbk Member

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    Thanks Horse,

    That's just what's so weird. Prior to starting my butt weld I played with the heat and wire feed on some cut-off pieces (same metal) to get things just right. Many of the welds do seem to get good penetration (nice blue haze around the tack). If I turn the heat up I get blow through and then have to fill with weld or where I feel it's too bad, weld in a small patch.

    One thing I'm thinking is that maybe the radius on the new quarter is not quite what the factory was so where the butt weld is it creates a ridge. I now have some wavy spots along the seam which I need to try and hammer and dolley slowly back to flat.
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  4. rbohm

    rbohm Founding Member

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    something i notice, your tack welds seem to be a bit cold, which means that when you work them, you end up removing most of the weld which then leaves you with a hole because the weld never really penetrated the metal properly. also dont get too aggressive with the grinder. the second picture tells me your welds are inconsistent, some really good ones, others too cold.
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  5. 65-Fstbk

    65-Fstbk Member

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    I have turned up the heat by one setting. One last small patch to clean up an ugly bit and it seems to be better. A little hammer and solely work to flatten and I'll scuff the whole seam with a Scotchbrite and then try some glass reinforced filler over top.
    Seems to be an incredibly fine line between a nice weld and blow through. Hopefully all good now.
    Thank you!!
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  6. horse sence

    horse sence Please don't call me Mom SN Certified Technician

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    With the thickness or thinness of mustang sheet metal it can be hard to get the proper setting on your welder .Primer or paint on the metal can cause trouble . The new metal doesn't always weld good either ,kind of like it is contaminated . Try stitch welding ,tack after tack and see if that helps .I know it helps keep warpage way down .When you get good at it it will look like a tig weld . Do maybe three tacks and cool with air then skip over about 6 inches and repeat keep going back and forth until you have welded the whole panel .Never blow air on a weld that is still red ,it will blow through like a torch.
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  7. rbohm

    rbohm Founding Member

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    true, welding sheet metal isnt easy for sure. i assume you are mig welding, and as such you should try to get the sound of the welding to sound like bacon frying. that is when you get as perfect a weld as you can with mig. also your tack welds can stand to be held a bit longer, about 1/2-3/4 second longer. and as suggested, move around a lot when welding sheet metal. make your tacks about an inch apart.
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