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Old 06-10-2011, 03:37 PM
artistmcgill artistmcgill is offline
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Default weld finishing

How does one go about finishing a lap weld joint? I have an angle grinder and have a flap disc I use to smooth butt welds, but because one side of a lap joint is higher than the other I worry about thinning the metal too much.

I need the piece to be as smooth flowing as possible. I'm considering using solder as a filler and then just grind it down till flush. Is there a better way to do this? The end product I would like to be a nice shiny metal, so no body filler or bondo please. Thanks~
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Old 06-10-2011, 05:02 PM
ClassicRestorations ClassicRestorations is offline
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Is it a body panel or a chassis(structural) piece?

If its body i would advise gaswelding and planishing.(no lapjoint)

When you are using a lapjoing and MIG welding it is almoast impossible to make it invisible.
Planishing these welds is not easy and will result in cracks.

The best you can do with these welds is leadloading them...
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Old 06-10-2011, 05:24 PM
artistmcgill artistmcgill is offline
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It's just a body panel essentially. I do not have a gas torch, so that's out. It doesn't need to do any load bearing, just look smooth and match the brushed/polished steel its mainly made from.
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Old 06-10-2011, 05:27 PM
ClassicRestorations ClassicRestorations is offline
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Maybe a Tig welder?

Otherwhise i would say Mig weld is without overlap, grind it flat at both sides and planish it a little bit or use lead.
Do watch out with planishing MIG welds!
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Old 06-10-2011, 07:20 PM
ShawnMarsh ShawnMarsh is offline
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If you need to finish the weld without filler, lap joints are out of the question. You have to butt weld with metal of the same thickness.
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Old 06-10-2011, 10:17 PM
Dyce Dyce is offline
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If you want to paint the panel a lap joint is not the way to go. Even if you get it straight the weld seam will show with temperature changes. My brothers 55 chevy is proof. On a nice hot sunny day one quarter will get a line in it where someone lap welded it.
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Old 06-11-2011, 06:45 AM
ojh ojh is offline
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As others have said, you are going to have to butt weld if you want that bare/raw metal seamless joint - can't even use lead as there is quite a color difference. I think you will have to learn to gas weld if you don't have tig, getting David Gardiners' DVD (he is the master at gas welding and knows how to explain it) would be a good idea.
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Old 06-11-2011, 09:14 AM
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jhnarial jhnarial is offline
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Like every one has said it has to be butt welded to do any kind of metal finishing to it. The reason for this is when you weld you are shrinking the metal and the only way you can fix it is to re-stretch it. You can not re-stretch through two layers of sheet metal, that you would have on a lap joint. So what ever distortion you have is locked in.

So what you need is a nice tight fitting but joint. Getting a good fit up is a thread in it's self.

The most important part of having a invisible weld is your line up while tacking. The metal has to be perfectly parallel with it's self, if it is up a little or down a little while tacking or welding you will never get it right unless you thin the metal.

If you mess up cut the tacks that are bad and fix it before welding.

After that you need to know how to re-stretch your welds.
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Old 06-11-2011, 05:46 PM
ShawnMarsh ShawnMarsh is offline
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While I think a butt weld is the only way to go, I disagree that you "need" to learn to gas weld or TIG weld to do it. I prefer those methods, but I have metal finished MIG welds in the past. When butt welding using a MIG, it is suggested to use a 1/16" gap to get good penetration. That is an I-CAR thing, and as much as I have tried using a tight joint with a MIG, I never get as good of results, so I'm back to using a small gap if MIG welding.

However, as stated, if my goal is to not use filler (I'm not good enough to actually achieve zero filler) I prefer TIG or gas. My TIG is much better than my gas and I only use steel at this point in my life, so that is my preference.
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Old 06-13-2011, 09:25 AM
artistmcgill artistmcgill is offline
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Thanks for the responses, all. Looks like I'll be making sure the pieces fit perfect next time.
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