Tanks A Lot | Sheetmetal Welding Tips and Tricks

10.For final welding the seams, I weld from one edge to the other only stopping briefly if necessary to adjust position. I do not skip around.

10. For final welding the seams, I weld from one edge to the other only stopping briefly i

Now that the steps have been taken to clean all contaminants from the surface prior to final welding, attention needs to be given to preventing contamination during the final welding process. The argon gas flowing from the torch shields the molten weld from oxygen and other gasses in the air that would otherwise readily combine with and contaminate the weld. Something that is often overlooked, however, is the backside of the weld that is still exposed to and contaminated by the air. This leaves you with a weld that is not sound all the way through. This might not seem like a big deal, but when there is less than 1/16 inch of steel separating you from several gallons of fuel, you can see the importance of a weld that is clean all the way through. To shield the backside, I use a combination of two methods. For most welds, I use a special backing tape. This is a 3-inch aluminum tape with a 1-inch woven fiberglass heat-resistant center. This is a trick I learned from my good friend, Fay Butler. His website, faybutler.com, is a good source for this tape. The tape is centered over the weld seam on the backside. When welding, a small amount of argon creeps through the seam and is held by the tape. When the tape is removed after welding, the clean weld shows how effective this method is. The final welds putting the bottom in the tank do not allow access to use the tape. So, for these welds, I purge the inside of the tank with argon. An easy way of doing this is to use a Y fitting, a second valve, and a small hose connected to the welder’s tank. Run the hose into the tank and seal with masking tape. I let the tank fill for a few minutes then I readjust the flow meter to 35 (CFH) then use the valve to restrict flow to the hose to about 15 CFH. This gives you 15 CFH flowing into the tank and 20 CFH at the torch.

11.Keeping a short arc and adding filler rod directly to the molten puddle rather than in front of it are two things that help keep the heat concentrated and allow full penetration with less total heat.

12.Here you can see how effective the backing tape was keeping the weld contamination free all the way through.

12. Here you can see how effective the backing tape was keeping the weld contamination fre

Now for the actual welding. Here there are a few common practices that I avoid. First, I always weld a seam continuously from one end to the other. I never use the practice of jumping around welding short stitches at a time. Oftentimes people do this because they feel it minimizes warpage by preventing shrinkage. Anytime you weld, the heat-affected zone shrinks as it cools. This shrinkage is the cause of warpage. I find having so many start and stop points increases chances of missing penetration in spots. By planning weld seams in areas that allow good hammer and dolly access as much as possible, the weld can be stretched back out after it cools. The high-strength motorcycle type shapes are more forgiving to warpage than flatter panels, but this is the same process I routinely use for welding roof skins in ’30s hot rods.

13.When the proper amount of filler rod is used, the weld bead is even and just barely above the surface. If too little filler is used, the center of the bead will be undercut and lower than the surrounding metal. Too much rod will result in valleys on either side of the bead after hammer and dollying.

13. When the proper amount of filler rod is used, the weld bead is even and just barely ab

The real key is that the shapes fit together well. If a lot of clamping pressure is needed to force the panels into alignment that can translate into larger amounts of warpage and unpredictable results. A good way of visualizing this is to imagine taking a 3-foot length of steel rod and bending it a small amount at a time along its length until it holds a gentle curve. Now if that piece of rod is heated with a torch in the center and cools, not much happens. Now imagine taking another rod, holding it at each end and flexing it to the same curve. Now a second person heats the center with a torch. In this case a large kink would develop because even though it was on the same curve, the second rod is under stress.