Auto Body Welding and Air Compressors

I'm getting close to cutting out rust and installing panels. I have a Century wire feed welder, MIG and flux-core, will flux core work for auto
body? I'm wondering since I don't use this very much I took my cylinder back instead of paying monthly rental. I can do a cylinder lease if necessary but if Flux core wire will work for auto body repairs then I can save some money.
Also, it appears I'll need a more powerful compressor. The compressor I'm most interested in right now is a Porter Cable 60 Gallon 3HP with a Cast Iron pump, these are running $599-$699 on the internet but the local farm stores have them for $399. I figure the 60 gallon tank being brand new would make that hard to beat, unless someone here knows of a better deal.
The Porter Cable 3HP compressor has around 10CFM at 90PSI, I have another compressor with 5.3CFM at 90PSI I can connect together if I need to. Also I have another compressor with around 3HP with a hole in the tank. Anyway, if I bought the $399 compressor with the 60 gallon tank, I could couple 2 more compressors and get close to 25CFM if I needed to.
RogerN
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Can you have owner bottles?

Thats like an equivalent of a 5 HP compressor. If you look around, you can find a decent 5 HP compressor, it will work forever and supply enough air.
i
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wrote:

Yeah, something like that anyway, lifetime lease or something like that. But if flux core wire will work just as well it would save me maybe $200 for the tank and gas.

In all I could hook up 2ea 3HP compressors and a 1.5HP compressor to get around 25CFM, I usually don't see over 18CFM maximum from 5HP compressors, though 5HP would be enough for about anything I plan to do, maybe some sand blasting. For the new compressors around here the single stage 5HP are $800 with a 60 gallon tank. At one time Rural King had a Quincy single stage 5HP 60 gallon for ~$600, I'd buy one of those if they were still available. Anyway, an extra $400 to step up from 3HP to 5HP seems steep since they both have 60 gallon tanks. I think I would be better off to buy 2 of the 3HP compressors and have 20CFM + 120 gallons of air tanks!
The portable compressor I have with 3HP and a leaking tank has a 30 gallon tank, pretty big for a portable. I don't like the idea of welding on a tank, it could have some compressor oil in there, might make flamable fumes. If I get energized to disassemble the compressor maybe I'll fill it with water and weld on it.
RogerN
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You can use the flux welder for plug welds; that's about it. Won't work for panel butt welds or lap joining, except maybe to spot weld the joints. It's almost impossible to run a seam in thin sheet metal with a flux welder. You really need to Tig it. JR Dweller in the cellar
wrote:

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On 06/27/2010 08:46 AM, JR North wrote: (top posting fixed)

(compressor stuff snipped)

> You can use the flux welder for plug welds; that's about it. Won't > work for panel butt welds or lap joining, except maybe to spot weld > the joints. It's almost impossible to run a seam in thin sheet metal > with a flux welder. You really need to Tig it. > JR > Dweller in the cellar > Or hammer weld it with oxy-acetylene. Not that this is a trivial skill -- it may take you less time to get a part-time job at McDonalds & save up for a TIG welder than it would take you to learn how to hammer weld a really good seam with oxy-acetylene. But it can be done.
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I haven't seen that done for 30 years, but someone who was expert at it tried to teach me once upon a time. He largely failed, or I just failed to learn. d8-)
It takes a lot of practice and a fine feel to know how much to "splash" the metal toward the weld with hammer and dolly.
I thought this was a lost art, and that everyone did this work with MIG these days, hammering down the bead a bit and then just grinding it off? It introduces a lot less total heat than TIG, and a great deal less than O/A.
--
Ed Huntress



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On Sun, 27 Jun 2010 15:34:44 -0400, "Ed Huntress"

The excess heat and consequent distortion is the problem with O/A. I can do hammer welding, or could at one time, but MIG and TIG make life so much simpler.
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I already have a TIG welder with a 350A liquid cooled torch. All the stuff I see on auto body is saying MIG weld, that oxy-acetylene and TIG makes too much heat in the panel and causes warping. I loved oxy acetylene welding in school, you could see what you were doing, welds were very solid, no slag to fight... but from what I have heard it doesn't work for modern automobiles, hopefully that's wrong.
RogerN
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On 06/27/2010 01:26 PM, RogerN wrote:

Oh, _modern_ automobiles...
I only ever learned oxy-acetylene welding, and that a long time ago and only to the stage where I was told that with lots more practice I should be really good.
I'm surprised that MIG is supposed to be better than TIG, but as I said I've been out of the loop.
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RogerN wrote:

I'm surprised to hear that it's thought that TIG puts in too much heat compared to MIG. My choice would be TIG and butt welds but that's my preference, on long joins at least. I'm not doing it for a living mind you. The longest external panel join I've done, read visible, was about 2' or a bit more letting in the bottom sill section of a rear wing on a Lancia Beta HPE. Usual procedure of tacking every couple of inches, hammering the tacks to counter contraction and keep the gap constant, then weld between the tacks and again hammer the weld. End result required very little filler in a few spots. I find that while MIG is quick you can then spend quite some time grinding back the weld and need to be careful doing it so as to not distort the panel from the grinding heat. For some shorter welds up to maybe 10" I have used MIG hot and fast and run a single weld in one pass to good effect but still care needed in the grinding.
BTW I've rarely used gasless and generally have heard it's not good for auto body sheet metal as it runs hotter and is more prone to burning through.
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    --Is that Porter Cable air compressor a red-painted vertical one? I got one a few years back and it had some serious teething problems that included sucking an air valve assy that required a visit from a P-C tech to fix. He then said that the valve had to be replaced every few months to keep the thing operating. Have also thrown the drive belt a few times. You might want to look to another brand.
--
"Steamboat Ed" Haas : Didja see my stuff
Hacking the Trailing Edge! : at 2010 Maker Faire??
  Click to see the full signature.
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I don't believe 10 CFM at 90 PSI with 3 PS, nor should you.You get what you pay for. Don't buy junk. Steve

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10CFM at 90 PSI seems to be a common rating for 3HP compressors, most other brands have compressor in the same range. Or course all these could be rated with the same amount of wishful thinking though :-) A friend at work has a Quincy single stage 5HP that is supposed to run around 16-18CFM at 90 PSI. I don't actually know anyone with a CFM meter for their air compressor but one of the reviews I read on the compressor said they were able to run two air sanders on the compressor. I just figure it would run most of my air tools, my 5.3 CFM runs most of my air tools, but I could couple it up with the 5.3CFM if it has trouble keeping up.
RogerN
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I'm hoping Iggy can find me one of these for maybe $25 though. Probably cost me $1000 for a drive and wiring though!
http://www.ruralking.com/compressor-2-stage-10hp-120gal-max.html
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Roger...mig works nicely with CO2. Im sure you can snag a small Co2 bottle someplace. I get em for little or nothing. Liquid CO2 costs damned little, and a bottle will last for literally hundreds and hundreds of hours of mig welding. A 20lb bottle can be had for less than $50..often far far less..and they are cheap to fill and last a very long time.
It should be noted that Co2 bottles are falling out of favor in bars, soda shops and whatnot as newer tech is employed..and there are literally Millions of them out there.
Just a heads up.
As far as welding with CO2..it does a really nice job, though the welds are not always as pretty as C25 or straight argon..they are as good or better than flux core, and actually make the machine "hotter" so you can weld at a lower power rating. And there is litle or no "clean up" after welding.
Gunner
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wrote:

I've not used straight CO2 so I won't knock it, but "hotter" is not a feature when welding 24-gage steel.
When considering the time spent and cost of good materials (paint, etc) for a decent job, the cost of Ag25 mix is completely insignificant, probably less than the cost of electricity to run the compressor doing all the sanding and grinding.
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On Mon, 28 Jun 2010 00:33:19 -0500, Don Foreman

But you can indeed turn it down to the next lower range in most cases...giving you plenty of welding ability and for cheap. But yes..C25 may be better if you have it. Trimix would work as well. But..its pricey

Your advice is noted.
Thanks!
Gunner
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wrote:

What is the ultimate? Perhaps auto bodies should only be welded 5032.1 feet deep in fresh water at a temperature of 72.549 degrees F with a certain PH? Didn't work, what kind of hat were you wearing? Ok, I'm being ridiculous, but like you say, if CO2 is hotter then perhaps you can turn the amps down, or maybe the flow up, or have it cooled otherwise... I dunno, but I doubt that the best method is any more than someone's trial and error that they had success with.
RogerN
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wrote:

I suppose you could spray paint by filling your cheeks with paint and then sneezing.
Trial and error tends to produce best results with a method that has technical advantage for one reason or another. That isn't to say that acceptable results can't be obtained with alternative methods.
I have visited a number of restoration shops and body shops. They all run Ag25, none that I've seen run straight CO2.
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On Mon, 28 Jun 2010 23:03:42 -0500, Don Foreman

I had a commercial welder over to the house yesterday, and he was wondering how long that tiny little bottle of gas on the back of my Mig lasted. I told him...about 6 months. He backed up, gave me a really funny look and a sneer. Then he read the lable on the bottle..and raised his eyebrows..asked...can you really weld with straight Co2?????
I fired it up, laid out some scrap and handed him a hood and the gun, and told him to have at it.
He ran some beads, beat some iron..and mumbled that it worked pretty damned well..and asked if Id told anyone about it?
Chuckle.....
Its not as common in shops as one would expect, which I find really odd.
Shrug
Gunner
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