Thread: 2nd shop gathering, metal shaping

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Man wish I could go -
I welded heavy metal for years - 25 years ago. Now I'm re-learning sheet metal MIG butt welding as I replace my Nova quarters and tail panel.

I only get ONE shot at it - one is done - one to go. Having issues with a tight enough fit and enough heat to have the weld lay down correctly. So on the first panel welds were cold and lots of grinding. But its stuck :-). Just now as much back side penetration as I know there should be.

All said and done - its coming together . . .

I'm thinking about spacing the quarter 1/16 low at the inner wheel well when I doing the cutoff wheel fit. Then fit it tight, to elininate the gap. All the gap is on the top edge, except for where it fits vertically at the door pilar.

I'm also running into some factory lead work (and brass braze tacks) on the corners where the tail panel ties in. Thats a whole other issue to tackle later.

Originally Posted by ojh

It was a great time, nothing quite like watching and listening to a couple master craftsmen - very impressive. It was so good a definitive DVD should have been made, i would buy a copy.
Thanks, oj

x2 on this. I would love to go to one of your gatherings, but it's just too far away. If you do a DVD next time, I would also buy a copy.

fun fun . back 30 years ago i did abit of lead work still have body work on my cars with lead i did .nice to see some one cares about the old way .not many do.. there s many bondo jockys out there. i did get a call from the boat yard they knew i leaded .they wanted me to lead a sail boat keel over head i did get it to stick there was abit on the ground they bang it pulling it out of the slip and crack the lead

Hi Nova,

I am sure by now that you have discovered that welding sheet metal is a whole lot different than structural steel. Basically, instead of running a solid bead you have to do stitch welding every few inches. After you get to the end you will have to go back and stitch weld between those every so many inches. Keep the welds going between the stitches until it pretty much fills up between them. Of course, when you say MIG welding, I am assuming that you mean with the use of gas. The flux core wire sucks. There is only one good place that I can think of for using flux core wire and that is to hold the trash can liner in the bottom of the can.
I always weld with .023 wire. .030 wire takes too much heat and burns through too easily. With .023 you can always turn the wire feed up to compensate if necessary whereas using .030 you can't and it takes more heat which will warp the metal worse and get a nastier looking weld because of trying to keep the heat low enough to keep from burning through. In certain instances I have found that I can weld a steady bead for maybe an inch (sometimes more) and let it cool while working farther on down the seam. Problem is, longer beads= more heat. More heat= more warpage.
It always helps if you have room to work the weld to take the stress out of it. In my younger days I always used to braze the sheet metal but the flux sometimes caused problems later on while trying to paint if you didn't get I all off. You will see most body shops use a MIG welder. I haven't seen anyone actually use Oxyaccetelyne in body work with mild steel since I was a kid but I see it is recommended for doing automotive sheet metal. Mostly because the MIG welds with about 10,000 PSI tensile strength and the gas welding is much softer and more workable.
Another thing I am sure that you have noticed, when butt-welding steel of any size at all you will typically leave a gap between the two base metals the diameter of the filler rod. You can't do that with MIG because it will blow away. You will have holes everywhere. You probably knew all this anyway.

i have butt welded many times with a mig but i use .030 wire if dial in it works fine fit up has to be dead on not for first timers so stick with .023 i was thinking back 30+ years ago up in the middle of a panle gas welding it not think to much about it that was the only way we had . alot of wet rags not sure i would want to do it that way now when done we use a wire wheel we called then mule skinners that would get the glas like fux off after brazing

Yeah, old geezers like me (I am not going to include you but you may be) used gas welding because there was nothing else. I learned to weld at 13 years old with acetylene by welding beer cans together end-to-end. After about welding 10 of them together my Dad would take them and strike them against the ground. If they broke he would tell me to do it again. I remember I was all grins when he finally struck them against the ground and they would not break. It was a real bear learning to weld something as thin as a beer can without burning it up.
When I bought my MIG welder it came with a roll of flux core wire. I hooked it up and started welding with it. I went about two inches, took the roll of flux core off the welder and threw it in the trash and went to buy a argon tank.
Personally, I like to use .023 wire. I can always turn the wire speed up if needed. .030 wasn't so bad on the older cars but the newer ones have such thin sheet metal it is hard to keep it from burning through. I have no problem filling in a burn hole. I can fill in a 1" hole easily without plating it. I have always had a tendency to burn hot but I move faster to compensate. While in the Air Force I had to certify on aluminum, inconnel, titanium, stainless, mild steel and two others. I had to weld samples that were .030 thick. I learned to move along. One bit of hesitation and there was a hole, and of course, a failure on the test. I had to certify in MIG, TIG, stick and gas. I also certified with low hydrogen on structural steel. I used to be pretty fair, but I am slowing down these days. I was an Aircraft Machinist but I was also required to be certified in welding. It was part of fabricating parts. It was also handy if I had my head up my rear and cut a part down too far, I could weld it up and machine it back down again.

well how old is old ? i am 47 i pick up my first gas welding set when i was 12 still have it before that i leaded with a propane torch . i had one of the sears torch setups that you burned a solid pug of some thing you put in a tube that you used along with propane that you could gas weld with . at work i did body tin and structure work were i welded many cars slice and dice s and had all the state paper work along with it. i hanged alot of tin and was still doing it for guys in town till i sold my wire welder . last thing i welded was a box side on a.2003 ford pickup so yep i know all about the thin stuff its getting thinnner

47???? You are practically still wearing diapers. I just turned 64. It don't seem that I should be that old except that nothing works as it used to and I hurt a whole lot more. Good chattin with you Pat.

Ed

Originally Posted by Hurst01

47???? You are practically still wearing diapers. I just turned 64. It don't seem that I should be that old except that nothing works as it used to and I hurt a whole lot more. Good chattin with you Pat.

Ed

well hell i have the body of a old man feels like a got threw in a bag and beat with a bat every day. that is why i left doing body work thats why i am on here not many can put up with my raw mood with out pain killers. sorry about stepping all over your post ojh

Great feedback guys . . .

Of course, when you say MIG welding, I am assuming that you mean with the use of gas. The flux core wire sucks.

Yep - got gas now. I actually DID weld the trunk pan successfully with .30 flux core. But it was NOT easy. I had to try it - and quickly realized it was not going to do an acceptable job on outer panels.

... typically leave a gap between the two base metals the diameter of the filler rod. You can't do that with MIG because it will blow away. You will have holes everywhere.

Actually on the first quarter, I had a gap equal to the cutoff wheel or slightly larger. I had to weld it colder than I liked to prevent blowout.

I gonna try to tighten that gap up on the second.

SBC, if you started with a machine set up with flux core and then converted to gas and solid wire, you'll need to open up your machine and swap the leads (the + and -). The machine should be set at the factory where the Flux core burns before the base metal, essentially to create your shielding cloud first. Due to this polarity setup, weld penetration suffers. When swapping to argon mix, there is no longer a need to burn the wire first, and reversing the leads will thus also improve the weld penetration.

Next, sheet metal is a totally different animal than welding up the thicker steels. Probably the most effective method is either TIG or Gas weldiing, using no gap, and no filler, for a strictly fusion welding process. Speed is your friend here, and since my TIG machine is not very effective/responsive on the lower amperage settings, I have relegated myself to using the MIG until such time as I can get a better replacement. Although most people have a mig in their home shop, the disadvantage over the previous two mentioned methods would be the extra consumables needed for dressing the welds, the particulate introduced into the air (breathing protection needed), and what some refer to as a harder weld that is especially prone to cracking. I'd be curious to see the quality of weld that they are having these cracking issues with, and I will say that I have never had any issue with cracking, and I am using a full penetration weld.

I think you'll quickly find that the tighter your butt joint is, the less chance you have of blowing holes. For 18-19 ga sheetmetal, I use a "dot welding" method, of only welding one dot at a time. Next, your heat setting used should be determined by the obtaining of a full penetration weld when welding the dots. If you don't get a full penetration weld, and it just looks like the bead is sitting on top of the metal, your heat is not sufficient. By the time you grind the welds down there will be little holding your patch in and a year or so of road vibration will undo all of your hard work. Now, if you do find you are still blowing holes, before turning down the heat, increase the wire feed. It's like this, if you have enough heat to perform the weld but not enough filler going in, somethings gotta give, hence a blowout. The less the gap, the less the chance of a blowout. Wider gap = more weld filler = more heat = more shrinking = your panel just moved from where you wanted it. Any welding operation you do will cause shrinking, holding a gap isn't going to change that. As far as the TIG welder, they seem to be even more prone to blowing out holes, where a very tight gap is almost a neccessity.

Now, using a hammer and dolly, planish out the weld dots as you go, this should help to counter the shrinking effects from the heat from welding, and then grind the proud of the weld dots off from both sides. I like to use a 1/16 cutoff wheel perpendicular to the weld. It has less contact patch than any other grinding method, so less heat buildup. (Stop just above the metal surface, and it can be dressed flush later with a 3" roloc) This will get the dots out of your way for welding and then planishing the next set of dots. If you were to strike some of the previous dots while trying to planish subsequent ones, you'll be moving the panel causing waves and distortion. Planish and grind as you go, and it helps keep the panel straight and in check. And just like Prell, lather, rinse, repeat. Here's a link to a pretty good thread on welding sheet metal patches, I think with your welding background this stuff will be old hat for you in no time...

http://www.garagejournal.com/forum/s...ad.php?t=53534

I did change the polarity for solid wire.
Looks like I only got partial penetration.
Guess I could weld the back side where penetration is lacking?
Or do you think what is shown is adequate.

For the most part it does have good weld penetration. If I were to guess, I would say not grinding down some of the welds between tacks may be acting as a heat sink for the next one. You'd now need more heat to get the same weld penetration, especially if the panel had cooled any substantial amount. The more mass you have there, in essence you're now welding thicker metal. To check it, I'd do any final sanding/grinding across (perpendicular) the joint, so if a spot is needing to be re-welded the crack (butt joint) will more readily appear and not be hidden in sanding scratches. Also, shine a spot light from the outside and view from inside the panel. It should show you really quick if something needs a touchup.

Here's one I did on a trunk weatherstrip channel replacement. (This is one I planished after the fact) It does show a couple misses there about an inch in from the left end of the weld, but the with consistency of the remaining welds, and not showing any light with the spotlight test, I felt comfortable leaving as is.

NICE - I think you're right about grinding the welds. Its the last tack between 2 previous welds that is not penetrating properly.

AND - rather than continueing next to the previous tack, I was welding midway between two existing welds. Its the last gap that didn't tie in like it should have.

Thanks for the feedback!

Good stuff guys! HooBoy, not exactly sure what i'm looking at Nova. One reccommendation is to spend a little extra time getting the metal nice and clean, even the back side.