228 Modern Welding Copyright Goodheart-Willcox Co., Inc. When welding multiple passes after the root pass, the lowest bead in a layer is welded fi rst. This creates a shelf for additional beads to be built upon. This is the same technique that is used in SMAW welding. Using an oval weave helps fl atten the weld face. A high weld bead is not desirable in GMAW or FCAW. A fl atter weld bead prevents weld slag in FCAW from getting trapped at the toe of the weld. A larger oval weave is used after the root pass. A restart must be done properly so there is no evi- dence of the restart. Figure 8-59 shows an example of a fi llet weld that was not restarted properly. 8.11.3 Groove Weld on a Butt Joint or Outside Corner Joint A square- or prepared-groove weld may be used for butt joints or outside corner joints. Figure 8-60 shows a U-groove weld in progress. The electrode center- line should be directly over the weld line. For best weld pool control, use a 15°–25° drag travel angle. The gun and electrode should also point upward slightly to keep the molten metal from sagging. Short circuit- ing transfer and pulsed spray transfer allow the molten weld pool to cool slightly. Figure 8-61 shows a GMAW butt joint welded in the horizontal position. To ensure complete penetration, watch for a con- tinuous keyhole through the root pass. More than one pass is necessary on thicknesses above 3/16″ (5 mm). To completely fi ll the groove, an electrode weaving motion may be required. The oval weave performs well in the horizontal position. Figure 8-62 shows a horizontal butt joint being welded. Goodheart-Willcox Publisher Figure 8-59. This weld made with GMAW has an unacceptable restart. The restart did not move backward to melt into the first bead crater. This is a defect because the weld is weak in the area of the restart. Direction of travel 15°–25° travel angle Keyhole Line perpendicular to the base metal surface Goodheart-Willcox Publisher Figure 8-60. A U-groove weld on a butt joint in the horizontal welding position. Note the keyhole at the root of the weld. Goodheart-Willcox Publisher Figure 8-61. A GMAW butt joint welded in the horizontal position. Bug-O Systems, Inc. Figure 8-62. A mechanized GMAW machine mounted on a track. The track guides the GMAW gun along the circular butt joint on this large tank.