254 Section 3 Gas Metal and Flux Cored Arc Welding Copyright Goodheart-Willcox Co., Inc. A fi llet weld is started in the same manner as a weld bead on a plate. The electrode and the arc are centered over the weld root. The welding gun should be held at about a 45° work angle to the base metal. The gun can be held in a backhand, forehand, or perpendicular position. FCAW uses the backhand position. See Figure 17-12. Be sure to use the proper electrode extension. Once the welding arc is started, a pool will instantly develop under the arc. Some side-to- side movement of the gun may be required to form a C-shaped weld pool. The arc should be centered over the weld root and kept toward the front of the pool. Watch the pool as you move along the weld joint. The pool should melt and flow into both pieces of the base metal. Keep the pool the same width as the weld progresses. Weld defects and ways to prevent them are discussed later in this chapter. Exercise 17-2 Making a Fillet Weld on a Lap Joint 1. Obtain two pieces of mild steel measuring 1/8″ × 1 1/2″ × 6″ (3.2 mm × 40 mm × 150 mm). 2. Clean both surfaces and edges with a wire brush. 3. Select the desired electrode wire and metal transfer method. Determine the suggested wire feed speed, voltage, shielding gas, and shielding gas flow rate. 4. Set the values on the welding machine. Adjust the shielding gas flow rate. 5. Place the two pieces together to form a lap joint. 6. Tack weld the pieces in three places on each side. 7. Place the weldment so the weld will be made in the flat position. 8. Position the gun over one end of the joint using the correct angles. It may be necessary to point the gun more toward the surface than the edge when welding an edge to a surface. 9. Press the switch and begin welding. 10. Make a fillet weld along the seam. Fill the crater at the end of the weld bead. 11. Make a second fillet weld on the other side. Inspection: The completed welds should be convex with evenly spaced ripples. The edges of the weld bead should be straight and should not overlap. Exercise 17-3 Placing a Fillet Weld on a T-Joint 1. Obtain two pieces of mild steel measuring 1/8″ × 1 1/2″ × 6″ (3.2 mm × 40 mm × 150 mm). Goodheart-Willcox Publisher Figure 17-12. These are the correct angles for the GMAW gun for making a backhand fillet weld on an inside corner joint in the flat welding position. The gun is held at a 45° work angle to the metal surfaces and a 20°–25° drag travel angle. 20°–25° 45° Horizontal weld face Direction of travel