What's inside
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A 7018 electrode can produce a strong, clean vertical fillet weld, but it rewards controlled technique rather than speed. The usual approach is vertical-up welding: start at the bottom of the joint and build the fillet upward in short, even steps. This gives better penetration and control than vertical-down welding, especially on structural steel or material 1/4 inch and thicker.
Equipment and settings
Use a DC stick welder with electrode-positive polarity (DCEP: electrode holder on positive) unless the electrode manufacturer specifies otherwise. Many 7018 rods will run on AC, but DC positive generally gives a smoother arc and more reliable penetration.
Choose the rod diameter according to the joint and the amount of heat the metal can accept. These are useful starting ranges, not fixed rules:
| 7018 diameter | Typical amperage | Practical use |
|---|---|---|
| 3/32 inch | 70–100 A | Thin plate, small fillets, root passes |
| 1/8 inch | 90–135 A | General-purpose work on roughly 1/4-inch material |
| 5/32 inch | 125–180 A | Larger fillets and heavier plate |
Start near the middle of the range and adjust after observing the puddle. If the rod sticks frequently, the arc feels weak, or the puddle will not wet the toes, increase amperage in 5-amp steps. If the puddle runs ahead of the rod, the edges melt away, or the slag traps easily, reduce amperage.
For a basic repair or fabrication job, a standard inverter stick welder with enough output for your rod size is usually sufficient. You do not need an expensive industrial machine for occasional 1/8-inch 7018 work, but make sure its duty cycle and output are adequate for repeated passes.
Prepare the joint correctly
Clean both pieces to bright metal. Remove mill scale, paint, oil, rust, and moisture for at least 1 inch on each side of the joint. A flap disc or wire wheel works for light contamination; grinding is better when scale is heavy. 7018 is less tolerant of dirty steel than many 6010 or 6011 electrodes.
Fit the pieces tightly and tack them securely. For a 90-degree fillet, check that the parts remain square after tacking. A large root gap can make the puddle sag through the joint. On thin material, a gap around 1/16 inch may help penetration, but excessive spacing usually makes vertical control harder.
Keep low-hydrogen electrodes dry. A freshly opened package is preferable. If rods have been exposed to damp air, follow the manufacturer’s rebaking instructions; do not casually bake them in a kitchen oven. Moisture can contribute to cracking, particularly in restrained or thicker steel. A simple 7018 rod storage oven is useful for regular welding, while occasional hobby work may be adequately served by buying small sealed packages and using them promptly.
Run the vertical-up fillet
Set the joint so you can stand comfortably and keep your helmet close enough for a clear view. Wear a properly rated welding helmet, leather gloves, a flame-resistant jacket, and boots that cover the ankles. Remove flammable material from the work area and provide ventilation; the flux coating produces welding fumes even when the arc looks clean.
Strike the arc at the bottom of the joint, then establish a small puddle. Hold a short arc—about 1/8 inch or less, roughly equal to the bare rod diameter. A long arc increases spatter, weakens shielding, and makes the puddle sag.
Hold the electrode approximately 90 degrees into the corner, with a slight 5- to 15-degree upward travel angle. Move upward slowly enough for the puddle to wash into both plates. For a small fillet, use a narrow side-to-side motion or small inverted-V pattern. Pause briefly at each toe, move quickly across the center, and pause at the opposite toe. The pauses fuse the edges; the faster center movement keeps the weld from becoming too convex.
Do not make a wide weave in one pass unless the procedure and material call for it. A weave wider than about two to three rod diameters can overheat the joint and trap slag. For a larger fillet, use multiple narrow passes instead. Let the first pass cool until it no longer glows, then remove all slag before adding another pass.
Handle starts, stops, and slag
At the end of a rod, do not simply break the arc over the middle of the weld. Lengthen the puddle slightly toward a toe, then release the arc or backstep a short distance. To restart, clean the crater and strike just ahead of it, then travel back through the crater before continuing. This reduces crater cracks and cold overlap.
Chip and brush every pass. Even a small strip of trapped slag can create an elongated inclusion that remains hidden under the next layer. Use a chipping hammer and a stiff wire brush, and inspect the toes for unfused edges before proceeding.
Common problems and corrections
| Problem | Likely cause | Correction |
|---|---|---|
| Puddle sags or falls out | Too much amperage, long arc, or slow travel | Lower heat, shorten the arc, and move faster through the center |
| Cold, rope-like bead | Amperage too low or travel too fast | Increase heat slightly and pause at both toes |
| Undercut along a toe | Long arc, excessive current, or no toe pause | Shorten the arc, reduce amperage, and hold briefly at the edge |
| Slag trapped between passes | Poor cleaning or an overly wide weave | Chip and wire-brush completely; use narrower passes |
| Rod sticks repeatedly | Amperage too low, damp rod, or touching the work | Raise amperage slightly and maintain a short arc |
Practice and inspection
Practice on scrap of the same thickness and orientation as the real joint. Make several beads while changing only one variable at a time: amperage, travel speed, or weave width. The finished fillet should have smooth toes, even leg lengths, and no visible cracks, pinholes, undercut, or slag lines. A convex bead is acceptable, but an excessively rounded bead can indicate poor wetting and insufficient effective throat.
For a structural or safety-critical weld, visual inspection is not enough. Use the required welding procedure, filler classification, preheat, interpass temperature, and inspection method specified for the job. A good-looking practice bead does not replace an approved procedure or qualified welder.