04-22-2008, 09:51 AM
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Registered User
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Join Date: Jan 2006
Location: Akershus, Norway
Posts: 53
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I was contacted on email referring to this thread. I hope it's OK to copy this to the thread without identifying the person. I do that since it seems I may have written something that might not come out as good purchasing advice. And anyway it was a very good question.
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We have gas, (O/A), Arc & MIG, (Miller 151 Mig-matic) at home. I see on the BB you recommend TIG, rather than MIG – why is that ? The reason I ask is that TIG is very expensive {local price deleted} I understand is has to do with heat being able to work the metal afterwards.
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Actually it's mostly because I have OA, MIG, TIG and stick, and I point out where I will prefer each of those. It's not that it cannot be done with one or more of the others. TIG is very nice for getting a nice weld with little warping and very nice to deal with after welding. MIG is a ***** on places where you need to straighten it and planish afterwards. What you gain in it being very quick when welding you waste on grinding and straightening afterwards. The MIG weld is very hard, so damaging the hammers and dollies. And the metal on each side of the weld will be more brittle because of the high welding temperature and rapid cooling.
If I were forced to give up all welding methods except one, it would take me 2 seconds to decide on the OA. It will put in more heat and thus warp more, but it (the sheetmetal) will stay very soft and workable. And if you have experience using OA, it will be much easier to master TIG when/if you get there.
I suggest you cut a lot of coupons let's say 15x30cm with one very straight edge (use a file if you must) and weld 2 of them together at those edges. Tack at 30-50mm intervals, grind if necessary and hammer (+dolly) those until the sheets are completely straight again. Then fill in between them and grind/straighten again. When you can do this every time and end up with a sheet that have no waves or oil-canning, you're ready to tackle the car body. If you can do it in less than one hour, buy yourself some beers, you deserve it.
And I might add:
So yes, it very much has to do with the ease of working it afterwards. But I'm willing to spend on equipment not just to get the job done and done good, but also to learn using it. I love learning!
One of the factors I forgot to mention is that OA is much less dependent on the weld site to be scrupulously clean. With MIG and TIG there must be no traces of rust, oil, paint or in short anything but steel within the heat affected zone. On old car bodies that very often rules them out because it is just not possible to get that condition. But very seldom is there one method that is the right one although there may be a preferrable one.
I just corrected the previous post too as I found I wrote TIG where actually MIG was used. Why? Because the closed box shape will make OA difficult with the heat being deflected back to the nozzle. The TIG machine was not close by but would have done it nicely. The MIG was there and in this place there will be more OA welding, so I'll run the flame over the weld to anneal the weld area.
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Einar (AT) eunet (dot) no.
1996 960 3.0 24V
1988 780 Bertone
1986 Maserati Spyder.
1995 Alfa GTV 2,0TS (4 sale)
1962 Alfa Giulia Spider
Last edited by ESjaavik; 04-22-2008 at 10:04 AM.
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