September '18

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SEPTEMBER 2018 THE SHOP 59 of the top layer removal with a grinding wheel, disc or grinding stone, leaving a thin coating of metal over the bottom layer. Then they switch to a cut-off wheel and precisely remove what's left of the top layer. It can be tricky to not cut into that bottom layer. One way to know if you're almost through the top layer is to look for the color of the metal to change. Some- times the heat from the friction of the abra- sive will cause the metal to change color—it will turn blue or purple just before the layer is completely eaten away. Or a slight line will start to appear as the top layer is almost worn off. There are some spot weld locations where the cut-off wheel is the preferred first choice due to its thin profile. For example, a cut-off wheel is the perfect size for removing the spot welds along a drip rail. These can be tricky areas, as the metal can be quite thin. One solution is to use a smaller-diameter cut-off wheel. The smaller diameter allows for greater precision when the location of the spot requires a careful and light touch. Some folks will remove the cut-off disc before it wears all the way down. They save these small discs for removing difficult spot welds. The grinding method averaged about 2 to 3 minutes per spot weld. PLASMA-GOUGING SPOT WELDS Plasma-gouging spot welds was definitely the quickest method we tested. One of the easiest ways to eliminate spot welds is to use a plasma cutting system. However, you will need to check to see if your plasma cutting system has a Gouge setting. If it does, then you can use it to literally wash away spot welds. In fact, if you're thinking of getting a plasma system, look for one with a gouge setting. The cut setting on a plasma system is like a laser—thin and sharp. The gouge setting is a softer, fatter arc and can be used to wash away metal, rather than cutting through it. For this technique, instead of trying to burn through the spot weld itself, the area around the spot weld is gouged away. When used properly, this method has little effect on the bottom layer of metal. Once the metal around the spot weld is removed, the top layer comes off. Then just grind away what's left of the spot weld on the bottom layer. The idea behind this technique is to hold the torch at a sharp angle and keep it Here's the basic torch movement of the plasma system technique. Start with the torch at a 30-de- gree angle next to the spot weld. As soon as you see the metal starting to melt, flip the torch up. This allows the metal to cool just enough so that the bottom layer doesn't get hot enough to melt. The torch is continuously moved up and down. If you're grinding spot welds, your favorite tool will be a grinding stone mounted on a cut-off grinder. This will quickly grind away most of the top layer of metal. SHOP_Sep18_recommend.indd 1 7/20/18 2:52 PM

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