191 Chapter 9 Nonstructural Panel Repair Copyright Goodheart-Willcox Co., Inc. lows and lowers small highs. Filing is used to identify high areas and low areas. Both sides of the panel must be accessible for picking and filing. A body file is flat or nearly flat. Files should be used on flat surfaces. On a panel with single crown, the filing should be done with the flat surfaces as shown in Figure 9-38. On a double-crown surface, the filing should be short so as to not cut into a crown. The file is held at a slight angle as it is pushed away from the technician’s body. Do not contact the metal on the return stroke. The file bites into the high areas and passes over the low areas. A couple of passes with the file will make bright shiny areas in high spots. You can see file marks on these spots. Also you can feel the high areas when filing. The file will drag when it hits a high area. After locating high areas, tap them down with a pick hammer. If the pick hammer is sharp, the area moved will be small and precise. A blunt pick hammer can be used to lower larger areas. When the high area has been removed, file the panel again. If the file glides across the panel without dragging or cutting into a high spot, look for low areas. Low areas are places that do not have any file marks. Low areas should be brought up from behind with a pick hammer. This process is called blind picking. A sharp pick hammer may raise a low spot up to a sharp point. If the sharp point is filed, the file may cut the top off the point, leaving a hole in the metal. To prevent this type of problem, do not raise the low spot above the surrounding metal. Additional filing and picking can be done to make the panel level. Do not file an excessive amount of metal from the panel. Doing so can make the panel too thin. If you plan to fill the low areas, stop picking and filing once all the high areas are level and the low areas are less than 1/8″ (3.2 mm) deep. A grinder can be used instead of a file during finishing operations. See Figure 9-39. A grinder can be stroked back and forth over the panel. If the grinding disc is held flat to the surface, it will identify the high and low areas, as a file would. A grinder will produce heat, so only use a grinder in this way on high-crown panels. As with a file, find and tap down the high areas and then raise the low areas. A sanding board or block can be used to iden- tify highs and lows on a low-crown panel. See Figure 9-40. The damaged area has been scuffed with 180-grit sandpaper on a sanding block. The clearcoat sands white. The paint is sanded off in high areas, exposing bare metal. In low areas, the clearcoat and paint is not touched by the sandpaper. The low areas remain shiny. Goodheart-Willcox Publisher Figure 9-38. When filing on a single crown panel, hold the file as shown here. Goodheart-Willcox Publisher Figure 9-39. Grinding across the panel will help you identify high spots. Grinder Goodheart-Willcox Publisher Figure 9-40. The shiny painted areas are low spots. The bare metal areas are high spots.