There’s a misconception among enthusiasts and even some professional body guys about welding sheet metal. The fact is that no matter how good or careful you are, metal WILL warp when you’re welding on sheet metal. We’ve heard all of the tricks in the book, but none of them completely stop the warping; only reduce or control it. The secret is that the heat and cooling from welding will shrink the metal around the weld seam to some degree. The only way to reverse the warpage is to stretch it back out. The best way to reverse it is to hammer on-dolly on the weld to stretch the metal back out. Gene Winfield has mastered the technique of planishing the welds or “hammer welding” (modern slang term, we know the blacksmith term technically means something different!) over the years when Oxy-Acetylene welding sheet metal. I decided to ask Gene for a quick how-to on this process and he was nice enough to let me shoot a short video of the process as he described the way he does it. Below is my abbreviated version of the process.
I’ll preface this by saying I know the technical term “hammer welding” is an old blacksmith term in which metal was heated so hot you could literally hammer two pieces of metal together. BUT, over the years that term has morphed and is now also used to describe the process of welding two pieces of metal together and planishing the weld joint flat while it’s still red hot.
The two types of welds that easily lend themselves to “hammer welding” are Oxy-Acetylene and TIG welds. That’s because they stay soft and can be planished and shaped like the base metal. MIG welds tend to be brittle and harder than the parent metal. They also cool VERY quickly giving you an extremely small window where they’re soft enough to hammer on. Oxy-Acetylene welds are the softest of the bunch, but controlling the heat in the panel can be VERY difficult when welding. The more you heat the panel, the more you will warp the metal and the more you will have to hammer and dolly the metal.
Gene is demonstrating this process on a 1950 Shoebox Ford being chopped at the 2015 World of Wheels in Chicago. The metal around the back window was all scratch built from four separate pieces and needed to be welded together. Gene mentions he starts by fitting the panels as tight as possible before welding. A tip he shared is to make the panels a little larger than needed and allow them to overlap. You can then tack weld the perimeter of the panels to hold them in place while you work. Then take a thin cut-off wheel and cut through excess that lays underneath. This allows the lower piece to sit flush with the other panel and can be clamped and welded with very minimal panel gap, all while keeping the overall shape consistent.
With the panels butted together and the edges tack welded Gene starts welding the seam up with a fine flame and a 1/16 filler rod. As he melts the parent metal he pushes filler rod into the seam for a few inches.
He then keeps the flame on the weld seam to keep it hot and swaps his filler rod for a post dolly. The heat from welding the panel seam has already started shrinking at the weld seam and has begun to sink down. He takes the post dolly and bangs it from inside upwards to bump the major sag out of the seam, he then quickly pushes upwards on the dolly on the seam and swaps the torch for a cross chisel body hammer.
He then proceeds to hammer on-dolly quite hard on the weld seam. You can hear a distinct ringing from the hammer striking the dolly through the metal. If you do not hear the ringing you need to push up harder on the dolly or make sure that it is centered under the area you’re striking. This process is done while the weld seam is nearly red hot to allow the metal to stretch back out easier. What’s happening is that the weld seam and the metal adjacent have a lot of tension from the molecules in the metal being condensed in a focused area due to the extreme heat and cooling of welding. By putting the metal between a dolly and a swinging hammer you are slowly stretching the metal out by striking on it each time (think of kneading pizza dough). This relaxes the metal and flattens the weld which in the end allows you to control the warpage in the panel. This is very important to keep the shape of the panel you’re welding. This can be done once the metal has cooled, but it does take more work and time to move the metal.
Some people like to take breaks between welding to allow the metal to cool or jump around on the panel to keep it from heating up too much. I’ve also seen some high end welders and coach builders weld a seam in one continuous pass. A weld seam becomes wavy and unevenly warped because of the variance in the heat affected zone of the weld. What does this mean? If you put more heat into one section of weld than another or if you weld longer in one section than another the heat affected zone changes and so does the amount of panel warpage. So if you have a TIG welder and can move quickly you can weld a seam continuously and keep the heat affected zone small and consistent throughout the panel. This means the warpage is the same throughout the seam and it takes equal amount of planishing to get the weld seam relaxed and back into the shape you want. I wouldn’t suggest trying this method until you’re VERY confident in your metal bumping and welding skills.
Gene is a master at controlling the heat and bumping the weld seam up as he goes. He likes to keep moving to finish the job quickly and commented that after the weld seam is completely hammer welded he will come back with the hammer, dolly, slapping and vixen files, and bullseye picks to fine tune any small low spots. He will the work the panel until the metal is ready for lead, filler, or primer and matches the shape of piece he’s welding.
As with anything everyone has their own way to attack a project, but I think everyone can take away something from watching an experienced metal fabricator or welder work. As Gene says “Everyday is a School Day”!
-Matt/EW
I want to find someone in the midwest to chop my trophy winning 51 ford,
You won’t find ESAB Easy-Grind anywhere. They’ve phased it out. Dunno why. Maybe because of it not having AWS Certification. But it is/was good stuff!
I never realized there were so many steps into getting the panels placed perfectly. It looks like your project turned out great. I haven’t started welding yet, but hopefully, sometime soon. I would love to fix a few projects around my yard.
ESAB Easy Grind is a low alloy welding wire is what you want I believe. You’ll notice that every MIG wire has a code number on it. It usually starts with E70 -something- #. This last number tells you how hard it is. The lower the number the softer the wire. 2 is the nicest to grind but you can only use it for panel repairs. a #7 or higher should be used for structure.
Have a look at this thread, http://www.jalopyjournal.com/forum/threads/mig-wire-help.428841/
It talks about using a low tensile strength mig wire for non structure repairs.
Hi Max,
When overlapping the panels you clamp the 2 pieces together and take a thin cut off wheel and cut the overlapping portion off. This can be done a little at a time as you tack weld the panel together or while using a number of clamps. The idea is that you create a perfect seam that has little to no gap that you can then butt the two panels together and weld and hammer as you work the seam.
Hope that helps!
I dont understand the tip that was discussed about overlapping the panels, are the weld joints lap joints? If you you overlap the panels then how is the lower panel going to sit flush with the other panel?
Very informative… I really like these how to’s. Like you say, everyday is school day…
Thanks…
Damn. When I got my MIG welder in 1984 I quit gas/hammer welding. I used to do exactly what Matt is doing, followed by lead work. I’m getting ready to chop the top on my 1941 Chevy (one of those “I’ve had it for 40 years cars). *I think* It’s pointless to try to weld the pillars with this method, but anything on large expanses, well. I’m open to learning. I’m an old dog but love the new tricks. I thought TIG would be the way to go but wasn’t happy with that particularly, maybe there’s a way to combine the use of a torch for additional heat, and TIG to do the actual welding. Incidentally, I don’t recall if it was on this site, but the method I’m going to use for the chop will leave the roof skin “pretty much” intact, moving the roof forward and adjusting the pillars to compensate for the angle change. Hope I don’t screw up and end up throwing the whole car away. Thanks for the tutorial, much appreciated.
Dave, do you have a place you buy this from? I can’t find it on the internet.
Thanks!
I have welded a few patch panels with a mig and had very good luck, no warpage. Heck , I even though this is easy. Then the last project , replace a rusted part of a lower door. I cut out the bad part, cut a new piece, tacked it in . That went well also . Then grinding off the high spots on the welds the panel warped, the whole door skin was like BOING BOING, I think it’s call oil canning. I think I have to cut more out and start over and hope for the best.
Hi David,
Could you give me a website where I can get this ES60-2 Can’t find anybody that has this product ,
Thanks Tom
My mistake, fat fingered that one! Thanks for catching that Tom.
Great Video This is a neat technique Ive tried it a few times but never had an experienced craftsman like Gene to follow More videos of this nature would be great. The Masters like Gene wont be able to share the techniques for ever. Even more detail would be great Like flame size and setting tip size regulator settings coolant rags beside weld? post quenching? Any thoughts or proceedures Gene would do himself and would share would be great then put it all in an on line Eastwood web library Thanks Jeff ps gas welding is becoming a lost art ! My own sons look at me like its alchemy when I gas weld Still very usefull!
If you don’t learn something from this you aint “going to school”.
Just for clarity it’s “heat affected zone”, or HAZ for short, and not “heat effective zone”.
Good article. Thanks.
I seen this happen with welding panels or trunk lids or roofs or fenders the amount of heat has to be kept low other wise you will have a big problem
MIG welder can name their sheet metal welds more ductile by swapping to dash 2 rolls of electrode. The ES60-6 that most folks use, is better for slightly corroded base metal, as the electrode has more silicon and tends to produce a harder, less ductile weld zone. The -2 rolls of ES60 (ES60-2) will not be found as easily, but can be ordered through the Internet. A sheet metal joint welded with dash 2 wire closely matches the parent metal of the original panel, and can be metal worked like a oxy/acet weld joint.