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Welding sheet metal

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Welding sheet metal. Well I have been practicing with my mig welder with gas on pieces of sheet metal while making patches for my tr3 fenders and can not get very good penetration and cannot get a long continuous bead that looks like much, perhaps I am asking for too much. I talked to a friend that owns a body shop and he maintained that the metal could be the problem. He suggested that I should use some metal from the period (1958) because the sheet metals that people get from Home Depot or a sheet metal shops have a different constitution and will not weld very well. I did not want to show my ignorance and debate the issue, so I was wondering if anyone else has experienced the same difficulty.
Steve
 
I got some 20 gauge sheet metal from an air conditioning shop. It had a higher carbon content then that used in autos of any period. Go to a scrape or auto wrecking yard and pick up a fender or door made of the same gauge.
 
Make sure that both pieces are absolutely clean. I usually grind a small chamfer at both edges to make a "V" with a scotchlok disk and then fill this as I weld.

Make a couple of quick tacks, then fill in the gaps. A long weld will overheat the metal and make it warp.

It doesn't have to look pretty, a right angle grinder will do that later.
 
Try turning up the heat and the wire speed down. When welding a bead it should sound like frying bacon, if it is too poppy sounding you temp/voltage is too low/wire speed to fast. If it is very fizzy, violent sounding and you are probably burning holes in the metal your temp is too hot/wire speed to slow.

Welding sheet metal is harder to weld well than thick metal. Practice running beads on metal like 1/8 inch plate until they look pretty. Also, you really can't run a bead on sheet metal, you will warp in to no end. You basically do an extended tack weld. You will do this at equidistant points around what you are welding. You keep doing this until all the dots form a continuous line, then grind it smooth.

You also need to take your time and not let the metal (in the vicinity of the weld) get too hot, you should be able to touch it with your hand about 1-2 inches away from the weld. once the metal gets heat saturated, leave it and come back to it once it is cool.

Good luck, it is not too hard but it definitely takes practice.
 
With sheetmetal of the thickness for fenders, I weld half and inch and wait a bit. Then I move along and do another half inch but a few inches from the first one. Don't expect that you will start at one end and go non-stop to the other end.
 
I have had the same problem. I needed to weld up the seat bottoms where there were cracks. I have a little Hobart 140, and at it's lowest setting (setting 1, speed 30, using gas), I end up burning through about 1 time in 5. And that's with me doing the smallest and shortest weld possible.

I fear that I may have to find a more suitable welder when it comes time to repair any panels.
 
There was a discussion of this recently in the Restoration forum. I posted the following link, there is a video on the page. Click on the play video. I am working part time in a restoration shop, the owner is very good with sheet metal; he uses this technique.

Mig welding for thin sheet metal
 
I agree.

I have just bought a Lincoln Pro-Mig 140 and it is many years since I did any welding, so this will be useful as I get practicing.
 
With my welds looking as good as some of those in the web site, I ground off the excess quite smooth. Then I used a power file which is similar to a beld sander, but the belt is not 4" wide like you use for doing floors. It's only 5/8" wide and looks like a sub-machine gun with the belt that comes out in front where you would think the gun barrel would be. It really works super and all my butt welds (side by side) are absolutely smooth and no TRA judge can see any deviations from the original contours.

BTW, I bought my first power file in Germany on a business trip. It was a 220 volt unit made in Europe by Black and Decker. I travelled back to England with it - no problem, - but when I was leaving Heathrow to fly home to Canada, the X-ray machine and the agents all collected to look at the X-ray and then called the supervisor while I waited. It looked like a sub-machine gun in the X-ray.

The supervisor came over to look at it and asked, "What is this?" I replied that it was a Black and Decker electric power file. He said Okay ! You can go. I questioned him how he could make such a sure decision just fron looking at the X-ray. He replied, "My wife works in the power file department at Black and Decker in Slough about 10 miles from here. Go ahead."
 
One thing I have learned is use the thinest welding wire possible. The guide chart on my welder says .024, but I was burning through quite a bit as well. I changed to .023 wire, and it was considerably easier to weld with much less burn through. I use a bit higher wire speed feed than recommended as well. My welds are not pretty, and take more grinding than they should, but I do get good penetration. I picked up my metal at Home depot, and it seems ok. I also used some sheet metal of an old Dodge caravan...doubt that the owner will even notice......but I didn't see any difference in weldability if that is a word. Both pieces do have to be absolutely clean though!
I think mostly, it takes practice...though.

Mikey
 
Are you trying to weld coated metal or white steel???
You must take off some of the zinc along the edges if it is coated. Forget long welds!!!! sheetmetal must be stitched carefully and allowed to cool or it will warp so badly you will have to buy a 55 galon drum of bondo!!
I run a body shop and have been doing this for 40 yrs.
Most beginers will weld a part that is better done with epoxy/welding.Get professional advise before making a dogs breakfast of it!!
MD(mad dog)
 
Thanks all you have helped much. My welding machine is a Craftsman, but I think it is basically the same as a Horbart with the four heat settings. It sounds like everyone agreed that a series of tacks is what I want to do, and I will try that. However, the breakfast with the dogs is a little confusing, but I will try and find an expert and perhaps take him out lunch. Back in the day, I worked on the Alaskan pipe line pumping stations as a carpenter, and I wish I had one of those tig welders here to give some free lessons.
Steve
 
The repair panels for the bottoms of fenders on all the Austin Healeys are meant to be epoxied into place with a step formed on the piece to hide behind or inside the fender out of sight. Then a layer of body filler about 1/32" thick leaves it smooth inside the fender where it covers the overlap. As a result, it's fast and it won't distort like welding can do.
 
Hi Don and thanks I was wondering about that. I thought if I welded the patch from the front it would take a lot of grinding to hide the weld, so I was going to ask if a guy should weld the patch from the back. Could I perhaps purchase some lower fender repair panels and epoxy them on a tr3 from the back ?
Steve
 
Good advice here! I would like to reiterate what MDCanaday said about grinding off the zinc. If you don't do that, you can really damage your lungs.
I use a TIG welder. I find that setting it up for pulse helps a lot. I set mine for 300 pulses per second. This reduces heating. I also find that if I can back up the weld with another piece of sheet metal, it holds the heat down. Use a piece that is 1/2" to 3/4" wide and straddle the seam.
When you butt weld, tack and then use a hammer and dolly as you go. continue on, then later fill in. As was said before, let it cool.
Weld from the front side. The back is usually pretty bad looking.
I practiced on a lot of welders before I bought my Miller 200 DL TIG. I found that I could do a much better job on this machine. It is spendy. The basic machine was on sale at $1800. Plus tank, helmet, and other goodies. Boy does it do a nice job!
 
rlandrum said:
I fear that I may have to find a more suitable welder when it comes time to repair any panels.
Click to expand...

Nah, the welder is not the problem, the Hobart Handler 140 is a great little machine.

As others have said, you need to tack the patch in place with a series of spot-like welds.
Just tack it in place at 4 or 5 places around the perimiter and then start splitting the gaps with more tacks. You can't run a continuous bead on 20 or even 18 gauge sheet metal. It will warp beyond belief.

Even when replacing sills, I tack the whole thing in place, then run a 1 inch stitch every 6 inches or so. And you can't ever have enough clamps.
 
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