occurs at the end of the joint. The least amount of arc blow occurs in the center area of the weld or joint. Arc blow may affect the quality of a weld. If arc blow does occur, the welder can take one or more of the following steps: • Place the ground connection as far from the weld joint as possible. • If forward arc blow is a problem, connect the workpiece lead (ground) near the end of the weld joint. • If backward arc blow is a problem, place the workpiece lead near the beginning of the weld. • Reduce the welding current to reduce the strength of the magnetic fi eld. • Position the electrode so that the arc force counteracts the arc blow force. • Use the shortest arc possible to produce a good weld bead. A short arc permits the fi ller metal to enter the weld pool before being affected. A short arc also permits the arc force to overcome the arc blow force. • Use run-on or run-off tabs on the joint. See Figure 12-6. • Change to using AC current with an AC- compatible electrode. Running a Weld Bead Making a weld bead is known as running a weld bead. A weld pool forms after the arc is started. A weld pool is the small pool of molten metal that is formed directly below the tip of the electrode. Filler metal melts from the electrode and is deposited in the weld pool. The weld bead then begins to form. The arc length determines the voltage and amperage across the arc. Therefore, the welder must work to maintain a constant arc length while welding. The normal arc length is about equal to the electrode diameter. A beginning welder should practice holding a constant arc length with one hand. Two types of weld beads can be made when welding: the stringer bead and the weave bead. A stringer bead is one made along a line without any side-to-side motion. The width of a stringer bead should be two to three times the electrode diameter. See Figure 12-7. Its height should be about one-eighth of the weld bead’s width. For example, a stringer bead made with a 1/8″ (3.2 mm) diameter electrode should be about 1/4″–3/8″ (6.4 mm–9.6 mm) wide. The height of the weld bead should be approximately 1/32″–3/64″ (0.8 mm–1.2 mm). As the weld bead reaches the correct width, the welder moves the electrode forward at a constant speed. A weave bead is one made along a line while the electrode is moved from side to side. See Figure 12-8. Weave beads should not be wider than six times the electrode diameter. Weave beads wider than this may cool too rapidly. Impurities may be trapped in Goodheart-Willcox Publisher Figure 12-5. The effects of direct current arc blow on the arc and electrode wire. As the arc is started (A), the arc is blown toward the center of the weld joint. In the center (B), the arc travels straight down. As the arc approaches the end of the joint (C), the arc and filler metal are again blown toward the center of the weld joint. Goodheart-Willcox Publisher Figure 12-6. Run-on and run-off tabs were used on this square-groove butt joint. The tabs allow the welder to completely stabilize the arc before reaching the actual weldment. The weld bead is continued past the end of the weldment and onto the run-off tab. A weld with minimal or no arc blow is possible when using such tabs. Direction of travel Arc and filler metal Workpiece lead (ground) A B C Run-on tab Run-off tab Chapter 12 SMAW: Flat Welding Position 171 Copyright Goodheart-Willcox Co., Inc.