Just came in from my first practise welds on an old trunk lid. I'm trying to butt weld. I used my cutoff tool with the thinnest wheel I could find.035 and cut a line about 10 inches long. I tried to butt weld it together. The gap seems too wide to do a good weld. I often would blow a hole. Then I made a copper spoon and held it behind the gap with one hand and held the welding head with the other. Seemed to make a big difference. Some questions I need help with.
1. After a few spot welds the spoon would not sit flat against the metal. Is it customary to grind the backside of the weld as one progresses? Does the backside have to be ground down ever? Seems ugly if it isn't.
2. What do bodymen use to grind down the mig weld on sheet metal? I was using my 4in. electric angle grinder with a course wheel. Seemed like it was grinding away a fair bit of the good sheet metal beside the weld. Maybe it was grinding away too much metal. Is there a flexibel grinding wheel with a certain grit I can use on my high speed air sander that would be better?

I use a copper hammer behind welds where I am filling a space.

I have a flange tool that attaches to an air hammer. It puts a 1/2 inch wide lip for the patch panel to fit into. It can be set to put the patch panel slightly lower that the body panel. Put in a few screws and weld a perfect patch the first time!

I use a grinder but work very slow and with the patch panel set in the slightly lower flange, I hardly scratch the body panel.

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Redrum (or Mike)

68 Corvette - 383 CI, 427 HP, 700R4, 12.56 @ 108 MPH
69 SS Chevelle - 502 CI, 610 HP, 2004R, 1320 unknown
97 Z-28 - totally stock still under 14,000 miles

"Oh, you hate your job? Why didn't you say so? There's a support group for that. It's called EVERYBODY, and they meet at the bar."
*Drew Carey

redrum...I saw an air tool flanger in the EAstwood catalogue. What advantage does it have over a manual vice grip style. Do I need both styles. How do you make a square corner with one of those panel flangers? I read some post here where people say to fill the backside with seam sealer if you use the flange method. What kind of seam sealer? brush on or caulking gun? Any brands of seam sealer better than others?

The advantage of the pneumatic flange tool over the vice-grip type is akin to the advantage a saws-all has over a hand hack-saw. Speed.

What would take you an hour to flange with a vice-grip type tool would take a minute with an air tool.

That 4in grinder is too much for that sheetmetal, you need a flexible grinder. The one I have is from MAC and only used for grinding, it has attachments to use 5in flexible discs. You can even buy an attachment for your drill its called a ROLEC disc, any body supply house should have this its very common. Your big grinder is heating up that sheetmetal way to much causing more warpage, those flex grinders still heat up but not nearly the amount that big one does. After I grind down with my flex I go to a da sander with 80 grit and to 180. Makes for a nearly unnoticable repair.

Even if you put seam sealer on the backside of the seam you still have a welded joint that will rust back in due time. take your time and learn to perform the butt weld, it is by far the only weld to make on any type of restortion...Eric

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1970 chevelle
1970 chevelle SS455 not a typo its a buick baby
1949 and 1972 chevy trucks
http://briefcase.yahoo.com/bc/sevt_chevelles

sevt chevelle is right. i've not seen one lap weld yet that didn't show itself under a little body flex, especially in the rear quarter area with a healthy big block up front. Get some .o20 wire and get the butt weld going. Plus it makes a flawless restoration when you can finish it smooth from the back side. Don't make long passes either, you will warp the SH&^ out of it.
I don't make a pass longer than a 1/4 inch, and I move around the panel to let it cool.