Replacing door skins, quarter panels, and other patch panels can take a lot of practice to get perfect. We have found that there are a few little tips to make a seamless repair much easier. My favorite is the use of a "backing strip" to connect the new and old metal. Below is a crash course on how you can use some thin backing strips from our new Patch Panel Install Kit to make a seamless repair that will last the lifetime of the vehicle.
First make your cut just above the damaged area. Be sure to clean the work area to bare metal and smooth out any sharp edges where the cut was made.
Next, take a one inch backing strip out of the kit, and cut it to the length you need. Then use the supplied 3/16" drill bit to make evenly spaced holes in the original metal (do not drill holes in the backing strip).
Now that the holes are drilled, take your backing strip and slide half of it under the original metal and clamp the two pieces together. We suggest using our Plug Welding Pliers. They have a copper support pad on them that helps reduce heat into the panel and helps avoid blow-through when making spot welds. The "V" in the top of the pliers makes it easy to pinpoint where you need to plug weld with the helmet down.
Next you can plug weld the backing strip to the original metal. You may want to practice a few times on some scrap metal to get a nice flat spot weld. You should only be holding the trigger for a few seconds when making a spot weld. The result of setting up your MIG welder properly will yield results like below. Remember, the flatter the plug welds you make, the less final grinding and filler you need to do!
Now that you have your backing strip in place, you can begin test fitting your replacement metal. Below you can see another reason why these backing strips are necessary in panel replacement; we can't always cut a perfectly straight line. Without a backing strip here, you'd have a tough time filling the gap without adding a small piece of metal. Trying to fill the void with weld would have caused major warpage in the metal.
Once you have confirmed your replacement panel will fit correctly, you can drill plug weld holes with the 3/16" drill bit in the replacement metal. Refit the panel and plug weld it to the backing strip. Once the panel is attached, you can now slowly spot weld the seam between the new and old metal. Remember to jump around from end to end when spot welding. This will help keep the seam from warping and causing more work to get the repair area straight.
Once you have the seam welded up, you can grind any "proud" welds down and proceed with sealer or filler. Use Eastwood Quality Flap Discs to properly blend the welds into the seam. No matter how small of an area, using this procedure when butt welding panels together can really make the difference in the final outcome of the repair.