190 Section 2 Nonstructural Repairs Copyright Goodheart-Willcox Co., Inc. Continue tapping until the heated area has cooled enough to touch. Next shrink the highest remaining area. This will gradually lower the stretched high area. An oxyacetylene torch (with a small tip) or a butane micro-torch can also be used to remove hail dents from a low or medium crown panel. The flame should barely touch the deepest part of the dent. The heated metal expands but is restricted by the surrounding cold metal, so it moves up. This upward movement may be enough to eliminate the dent. If not, repeat the process. See Figure 9-35. Another shrinking technique does not use heat. Instead, the stretched metal’s surface area is reduced by kinking. Kinking involves the use of a shrinking hammer (serrated-faced hammer) or a sharp pick hammer to reduce the surface area by gathering the metal together. To use a shrinking hammer, push up on the stretched low spot with a flat dolly. Tap the bulge with the shrinking hammer. Hammer taps should be off-dolly but close to the dolly’s edge. You will notice that the serrations on the hammer face produce small kinks on the metal’s surface. Continue tapping until the metal is level. To use a pick hammer for shrinking, place a flat dolly on top of the stretched area as shown in Figure 9-36. Tap up on the stretched metal with the pick hammer. The dolly prevents the metal from moving too far. The pick hammer raises and shrinks the metal at the same time. Beginners often encounter problems when repairing a low-crown panel, such as a hood. Consider the front of a hood that is damaged, bumped, and filled. The technician may find a high area around the sanded filler. As the next step, the high area is tapped down then more filler is applied and sanded. Another high area is discovered adjacent to the filler’s edge. The tapping, filling, and sanding process is repeated. This is called chasing the dent. Chasing the dent occurs because the low-crown metal is floppy and is easily pushed in. The pressure from sanding causes the floppy metal under the filler to be pushed down. To prevent chasing the dent, tighten any floppy metal around the area to be filled by making a shrink fence. A shrink fence is a line of small kinks made with a sharp pick hammer. See Figure 9-37. The shrink fence tightens the floppy metal in the low-crown area, allowing the filler to be sanded level. Technicians sometimes oversand the filler. The excessive sanding leads to undercutting, a condition in which filler is sanded below the level of the adjacent metal. When comparing the filler height to the height of the adjacent metal, the technician misdiagnoses the undercutting problem and taps down the adjacent metal rather than refilling the low area. Undercutting should not be confused with chasing the dent. Picking and Filing Picking and filing are operations performed at the end of the roughing out process. Picking raises small Goodheart-Willcox Publisher Figure 9-35. A butane-powered torch can be used to raise small hail dents. Butane torch Goodheart-Willcox Publisher Figure 9-36. Kinking with a sharp pick hammer will reduce surface area in stretched metal. Stretched metal Dolly Goodheart-Willcox Publisher Figure 9-37. This diagram shows a low-crown hood. The Xs mark the kinks of the shrink fence. After forming the shrink fence, strip or sand the paint in the area of the shrink fence. Add filler or putty as required. Low area to be filled X X X X X X X X X X X X