Vertical and Overhead Fillet Welds

Why Out-of-Position Welding Is Different

Flat and horizontal welds have gravity working with you: the molten puddle stays in the joint. Vertical-up (3F) and overhead (4F) fillet welds fight gravity the entire time. The puddle wants to sag, drip, or run ahead of the arc. Controlling it requires specific adjustments to machine settings, gun angle, travel technique, and how fast you move. Master these two positions and you are prepared for the majority of structural steel field work covered by AWS D1.1.

Heat Management: Reduce Voltage for Out-of-Position Work

The single most important machine adjustment is reducing heat. A molten puddle that is too large and too fluid will sag before it solidifies. For GMAW short-circuit transfer with ER70S-6 wire on ¼" A36 plate, your Welding Procedure Specification (WPS) will direct you to drop voltage roughly 2–3 V below your flat-position setting. Wire feed speed (which controls amperage) may also be reduced slightly. Always follow the WPS — it is the governing document for the weld. If the puddle is sagging or dripping, the first corrective action is to reduce voltage or increase travel speed, not to fight it with gun angle alone.

Vertical-Up (3F) Fillet Weld Technique

For a T-joint in the 3F position, the workpiece stands upright and you weld from bottom to top. Vertical-up produces better fusion and mechanical properties than vertical-down for structural fillet welds; AWS D1.1 requires vertical-up for most structural applications unless the WPS specifically qualifies vertical-down.

Gun angle: Hold the gun so the wire bisects the 90° joint angle — approximately 45° to both plates. Tilt the gun 5–10° upward (push angle / forehand) in the direction of travel so you are looking into the puddle. Some welders use a slight drag; stay within the WPS limits.

Triangular weave: Move the gun in a triangular or "Christmas tree" pattern. Start at the root, pause very briefly at each toe, then swing back to the center before moving upward to the next leg. The pause at the toes fills the corners and prevents undercut. Moving through the center too slowly causes buildup and sag in the middle of the bead.

Travel speed: If the puddle starts to sag, speed up slightly or tighten the weave. Do not let the arc get ahead of or behind the puddle.

Cold lap warning: Cold lap (overlap without fusion) appears as a smooth, rounded toe that seems to roll onto the base metal without fusing. It is caused by too-low heat, moving too fast, or dragging the gun so the arc cannot reach the toe. Instructor demonstration will show you the visible difference between a properly fused toe and cold lap.

Overhead (4F) Fillet Weld Technique

The 4F position places the joint above your head. Spatter and slag fall directly toward you, making PPE non-negotiable. Gravity pulls the entire puddle downward, so puddle size must be kept small.

Gun angle: Keep the gun perpendicular to the joint (bisecting the 90° angle) with a 5–10° drag angle in the direction of travel. A drag angle lets you see the puddle and keeps the shielding gas envelope stable.

Short-circuit transfer: Use short-circuit transfer (the low-voltage, low-heat GMAW mode) for overhead work. It produces a smaller, stiffer puddle that is far easier to control than spray or globular transfer overhead.

Travel speed: Keep it steady and brisk enough to prevent buildup. A consistent stringer bead is preferred over a weave for most 4F fillet welds — a weave creates a larger puddle that is harder to control overhead.

Signs of trouble: Dripping metal, excessive spatter, and an irregular bead face all indicate too much heat or too slow travel. Reduce voltage or increase travel speed.

Reading the Bead After Welding

Once the coupon cools, use your fillet weld gauge to measure leg size. AWS D1.1 visual inspection criteria for fillet welds include:

• Leg size within the tolerance stated in the WPS (typically ±1/16" from the specified size)
• No undercut on the base metal face exceeding the code-permitted depth
• No overlap (cold lap) at the toes
• No visible surface porosity
• No cracks

Fill out your self-assessment form after each coupon — write down what you see and what you will change next pass. This habit is required for the lab and mirrors the documentation discipline expected on the job.

Safety for Out-of-Position GMAW

PPE: For 4F welding, full leather welding jacket (or FR jacket with leather sleeves and apron) is mandatory — sparks and spatter will shower your upper body and face. Auto-darkening helmet, leather welding gloves, and leather boots are required for all positions.

Spotter requirement: A second person must be positioned as a safety spotter before any student begins 4F welding. The spotter watches for fire hazards, falling hot metal, and cable trip hazards.

Ventilation: GMAW produces fume. Work in areas with local exhaust ventilation or general shop ventilation. Keep your head out of the fume plume.

Hot metal: All coupons are hot after welding. Use pliers or fixture handles. Mark hot metal clearly and never set it where another student could grab it.

Electrical safety: Inspect the gun liner, cable, and work clamp before each session. Never weld with damaged insulation. The machine should be off when you change wire or adjust drive rolls (follow your shop's lockout/tagout procedure).