in position prior to the main welding of the joint. The tack welds become part of the completed weld. Tack welds must be done well, or a defect in the completed weld can result. A tack weld is often 1/2″–3/4″ (13 mm–20 mm) in length. It must have complete fusion, or melting, into both pieces of metal. It must have complete penetration. All slag must be removed after making the tack welds. Fillet Welding A fi llet weld may be made on a lap, inside corner, or T-joint. The legs of the fi llet are usually equal. Normally, the size of each leg is at least equal to the thickness of the metal. Lap Joint In a lap joint, the weld is made along an edge of one piece and the surface of another piece. The electrode holder is tilted about 20° from vertical in the direction of travel. This is a 20° drag travel angle. The electrode should point more toward the surface when welding thinner metal. This is not as necessary when welding thick metal. The electrode should be held at a 45° work angle when welding metal over 1/4″ (6.4 mm) thick. See Figure 12-17. After the arc is struck, lay a stringer bead deep into the root of the joint. A C-shaped weld pool should be created. A C shape at the leading edge of the weld pool indicates that both the edge and the surface are melting. Reduce the travel speed if the C shape does not form. A welder can determine the correct forward speed by watching the rear of the weld pool. It should be oval-shaped. Thick metal may require more than one weld pass. Each weld pass must be cleaned before the next weld pass is made. The correct sequence of the weld passes in a multiple-pass weld is suggested in Figure 12-18. A multiple-pass weld contains more than one layer. Each layer may contain more than one weld bead or weld pass. The fi nal pass may be a weave bead if the bead width is not too wide. Inside Corner or T-Joint A fi llet weld for an inside corner or T-joint is made along two adjacent surfaces. The electrode will have about a 20° drag travel angle and a 45° work angle. The fi rst weld pass must be made deeply into the weld root. The leading edge of the weld pool must be C-shaped. This ensures that fusion is occurring on both surfaces. Each weld pass or weld bead must penetrate the base metal and/or the previous weld beads that it touches. See Figure 12-19. A weave bead may be used for the fi nal weld pass. Exercise 12-2 Fillet Weld on a T-Joint in the Flat Welding Position 1. Obtain three 1/8″ (3.2 mm) diameter E6010 electrodes, six 1/8″ (3.2 mm) E6013 electrodes, and three 5/32″ (4.0 mm) iron powder electrodes, such as E6027. 2. Also obtain four pieces of carbon steel measuring 1/4″ × 2″ × 6″ (6.4 mm × 50 mm × 150 mm). GFEDCB A Goodheart-Willcox Publisher Figure 12-16. The effects of current, arc length, and travel speed on covered electrode beads. A—Correct current, arc length, and travel speed. B—Amperage too low. C—Amperage too high. D—Arc length too short. E—Arc length too long. F—Travel speed too slow. G— Travel speed too fast. Chapter 12 SMAW: Flat Welding Position 177 Copyright Goodheart-Willcox Co., Inc.