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Tips for Welding Sheetmetal

Spot welds and panel replacement.

When repairing an older 4x4's bodywork, you'll occasionally find out that the path of least resistance to the repair is to remove and replace a body panel. This could be due to rust or severe damage that you can't pound back into its original shape. Sometimes a replacement panel is available from the aftermarket, and other times you have to custom make your panel out of flat sheet steel. This is something we've ended up doing several times, and we can give you some tips and tricks to make the job that much easier. One of the most important pieces of information you'll need to know is how thick the sheetmetal is. Generally, thicker sheetmetal is easier to weld to, and older 4x4s use thicker sheetmetal. Knowing the thickness will help you set your MIG welder so it won't blow through the material.

Spot Welds

Just like with practically any mechanical repair, you must have some background to get started with, and working on sheetmetal is no exception. First, it's a great idea to know what a spot weld is and how to identify and remove them. Generally, mass-produced vehicles have body parts held together by a spot welder. This type of welding makes a small round indentation where it bonds two panels together. Basically, two electrodes pinch the two panels together and send an electrical charge through the panels, melting them together. If you need to remove a panel, chances are you will have to drill out a few spot welds and learn how to replace them. The easiest way to deal with spot welds is to use a spot weld cutter. There are a few kinds, and our preference is these Blair spot weld cutters from Summit Racing. They take a little getting used to, but once you figure out the tool they cut fast and last well. We also recommend buying some replacement cutters for these tools. If a tooth or two break off the cutter, you'll either need to flip it around or replace the cutter, which threads onto the mandrel with the spring and centering pin in it. They work like a little hole saw with a spring-loaded centering pin. Punch the center of the spot weld, and get to cutting.

Holding Things in Place

Once you've removed the damaged sheetmetal and found or made a replacement, you must re-install it. Now, you could buy a spot welder, but we wouldn't unless you can get a good deal or plan on doing lots of panel replacement. Or you can do what we do and drill small holes (about 3/16-1/4 inch in size) in one of the panels to re-create a spot weld or rosette weld with our MIG welder. With that done, clean the underlying metal and apply weld-through primer. Then we use a series of different clamps to hold things in place before making our spot welds. You can usually fill the hole easily and make a lowercase "e" motion in the hole, filling it. Once you get good at it, the surface of your new MIG spot weld should be about flush, or you can grind it down with an angle grinder for a better look if there is a blowout or the spot weld stands up too much.

Forcing Things to Fit

Sometimes things don't line up as they should, new replacement panels may not have a perfect fit, and the metal you left may have been damaged, and you must use force to get it into the correct spot. Again, clamps are helpful, as is a body hammer and dolly. Also, we've used ratchet straps to hold things in place, and while most body shops may frown upon the idea, we sometimes use self-tapping screws to temporarily hold a panel in place. With one or two of the spot welds filled next to the self-tapper, you can remove the screw and weld up the hole. If you are worried about burning through the hole, you can back it with a piece of brass or copper, or a specialty brass welding spoon. Also, sometimes after doing a few spot welds you'll want to use your body hammer to pound some of the unwelded holes flush with the metal behind them. This won't work unless some of the welds are holding the panels together.