Chapter 3 Welding Joints, Positions, and Symbols 53 3.3.3 Penetration A completed weld joint must be at least as strong as the base metal. The weld must penetrate deeply into the base metal to be strong. Penetration is the depth of fusion of the weld below the surface. Total (100%) penetration occurs when a weld penetrates through the entire thickness of the base metal. Generally, total penetration is required only on a butt joint. The edges of thick metal may need to be machined or fl ame cut to achieve 100% penetration. Thick metal also may have to be welded from both sides of the joint. 3.4 Welding Positions Welders often must weld in a variety of positions. Welds may be made in the fl at, horizontal, vertical, or overhead welding positions. See Figure 3-15. On welding drawings, these positions are often abbreviated in the tail of the welding symbol as F, H, V, and O. The Amer- ican Welding Society refers to welding positions with a number and letter combination. Groove joints in the fl at, horizontal, vertical, and overhead positions are referred to as 1G, 2G, 3G, and 4G, respectively. Fillet joints in the fl at, horizontal, vertical, and overhead position are desig- nated as 1F, 2F, 3F, and 4F, respectively. Welding positions are determined by the posi- tions of the weld axis and weld face. Figure 3-16 shows the weld axis and weld face. The weld axis is an imag- inary line running lengthwise through the center of a completed weld. The weld face is the exposed surface of a completed weld on the side on which the welding was done. Figure 3-15. Each of the fi ve basic weld joints may be made in four different welding positions. Butt Joint 1G 1G 1F 1F 1G 2G 2G 2F 2F 2G 3G 3G 3F 3F 3G 4G 4G 4F 4F 4G Flat Horizontal Vertical Overhead Corner Joint T-Joint Lap Joint Edge Joint Figure 3-16. The weld axis is an imaginary line running lengthwise through the center of the weld. The weld face is the exposed surface of the fi nished bead. Weld face Weld axis