How incorrect SMAW current settings lead to undercut and excessive burning in welds

Outline (quick preview)

• Why current settings matter in SMAW: arc behavior, heat, and bead quality

• What happens when current is off: the key effects—undercut and excessive burn

• Reading the bead: signs that tell you current is mis-set

• How to dial in current in practice: a practical, easy-to-remember approach

• Quick checks and safety notes

• Real-world mindset: staying curious and methodical

SMAW current: why it matters and how it feels in the shop

If you’ve ever tuned a guitar amp or adjusted RPM on a machine, you know that settings shape the result. In Shielded Metal Arc Welding (SMAW), current is that shaping force. It tells the arc how hot to burn, how much metal to melt, and how the puddle behaves as you move. Too little current, and the arc is shy; too much, and the heat goes overboard. The balance you strike determines whether the weld looks clean, penetrates properly, and holds up to stress. In other words, current is not just a number on a dial. It’s the bridge between technique and integrity.

What happens when current settings aren’t right? The bottom line

Let me explain with a simple truth you’ll see echoed in the lab: incorrect current settings in SMAW can produce welds that are either undercut or excessively burned. It’s a clear, tell-tale sign that something in the arc dynamics isn’t singing as it should.

• Too low current: the bead might sit on top of the metal, barely fusing with the base. The weld may look decent at first glance, but the underlying joint is weak. You can get lack of fusion, and in some cases a shallow penetration that doesn’t reach the full thickness you’re joining. The surface might show a neat line, but the real strength is missing.

• Too high current: the arc delivers more heat than the workpiece can swallow. The puddle thickens and flows aggressively, sometimes burning through the metal. You’ll see a larger, more irregular bead, increased spatter, and a bead that’s overly convex or “burned” in places. In the worst cases, you introduce porosity and cracks—issues that nibble away at long-term reliability.

The practical takeaway is straightforward: if you see a bead that’s either too shallow or too aggressively melted, the current setting is off. And yes, this is exactly the kind of clue a good welder uses to adjust on the fly.

Reading the bead: what the signs tell you

Bead quality is your quickest feedback loop. Here are the tell-tale signs you’re dealing with incorrect current:

• Undercut: you’ll notice a groove along the base metal next to the weld. It looks like a tiny canyon that the weld metal didn’t fill. Undercuts weaken the joint and make it harder to meet spec on strength and appearance.

• Excessively burned bead: the bead is wide, rough, and may resemble a crater. There can be a feathered edge, and you might see slag coverage changes or porosity if the heat is too high for the metal and plate thickness.

• Inconsistent penetration: sometimes you get good fusion in one area and shallow fusion in another. That inconsistency is a red flag that current (and possibly travel angle or speed) is not uniform.

• Spatter and porosity: extra heat can push molten metal into tiny pockets with gas bubbles. Porosity compromises watertight or pressure-containing joints.

These observations aren’t just aesthetics. They point to how well the joint will perform under stress, vibration, or load. In a shop setting, where you might be welding on steel frames, brackets, or structural members, those subtle bead cues translate into real-life safety and durability.

Dialing in current: a practical approach you can use

Here’s a simple, repeatable way to fine-tune SMAW current without overthinking it. The goal is to establish a reliable starting point, then refine as you observe the bead.

1. Start with the electrode and metal thickness in mind

• The size of the electrode (for example, 1/8 inch vs 5/32 inch) and the thickness of the base metal set the baseline amperage range. Heavier plate can tolerate more heat; thin material needs restraint.

• Use the electrode manufacturer’s recommended amperage range as your anchor. This gives you a safe starting window.

2. Set the arc length and angle

• Keep the electrode roughly at a 15-degree angle from perpendicular to the work, and maintain a short arc length—just enough to sustain a steady arc without dipping into the puddle.

• A consistent arc length helps the current work its intended job: heat, penetration, and fusion, not a wild ride of melting.

3. Make a small test strip

• On a scrap piece, run a short bead at the low end of the current range, then a bead at the high end.

• Observe the changes in bead shape, penetration, and spatter. You’re looking for that sweet spot where you get good fusion without burning through.

4. Narrow it down with a single pass, then a second pass

• After you’ve identified a starting current that yields clean fusion but not burn-through, try a second bead with the same settings to check consistency.

• If the second bead behaves similarly, you’ve found a reliable setting for that material, electrode, and position.

5. Document and repeat

• Note the electrode type, plate thickness, joint type, travel speed, and the current setting that worked. Revisit the settings any time you switch materials, positions, or electrode sizes.

What to watch for in real-world welding

In daily work, you’ll balance heat, speed, and technique. A few practical tips:

• Watch your travel speed: faster can starve the puddle, making under-penetration more likely even if the current is on the higher end. Slow down a bit if you notice shallow fusion.

• Mind the position: overhead or vertical-up positions behave differently from flat. You might need to nudge the current up or down when changing positions to preserve stable fusion.

• Consider the environment: moisture in electrodes or rust on the workpiece can introduce porosity. Keep things dry and clean, and let the arc be your friend, not your foe.

• Check your equipment: if you see erratic current readings, inspect connections, leads, and the electrode holder. A loose ground or worn contact tips can masquerade as a current problem.

A few quick fixes if you spot undercut or burn-through

• If you’re seeing undercut, try a slightly higher current, or reduce travel speed a touch. Sometimes a tiny arc length adjustment helps.

• If you’re seeing burn-through, back off the current a notch and temper with a slower travel pace. Double-check the electrode angle; a little tilt toward the weld can help the puddle fill more evenly.

• For both issues, ensure the joint fit-up is correct and the base metal is clean. Contaminants and gaps don’t help margin for error with SMAW.

Safety and mindset notes to keep you sharp

SMAW can deliver strong, reliable welds, but it’s a technique that rewards discipline. Always wear appropriate PPE—helmet, gloves, jacket, and boots. Work in a ventilated area, and keep a fire watch nearby if you’re near flammable materials. And here’s a mindset nugget: treat every bead like a conversation with the material. If it’s not telling you what you expect—look, listen, and adjust with purpose.

Real-world context: why this matters beyond a test label

The truth is, current settings aren’t a one-size-fits-all dial. They’re a reflection of the metal you’re welding, the electrode you’re using, and the position you’re in. When you nail the right current, you’re not just passing through a set of numbers—you’re building consistency, trust in your own hands, and the confidence to take on tougher joints. That is the kind of skill that makes a welder stand out in the shop, whether you’re building carbon steel frames, repairing machinery, or creating custom fabrications.

A quick mental model to keep in your toolkit

Think of current as the heat dial for your metal: too hot and you smear the bead and risk burn-through; too cool and you fail to fuse deeply enough. The aim is a bead that’s nicely filled, with a smooth surface, and a clean line where the base metal and weld metal meet. You want penetration that confirms the weld ties into the base material without leaving a weak seam. This mental picture helps you calibrate when things start to feel off at the bench.

Closing thoughts: stay curious, stay precise

SMAW is both art and science. The correct current setting doesn’t simply fix a problem—it reveals how the arc, the puddle, and the metal cooperate. The fact that incorrect current can lead to undercut or excessive burning is a useful guidepost. It tells you where to look, what to adjust, and how to read the bead as a reflection of your technique.

If you’re ever unsure, go back to basics: clean work, stable arc, consistent travel, and a test bead. With each session, you’ll sharpen your eye for the bead, your touch with the electrode, and your confidence in the current you choose. And soon enough, you’ll be spot-on not by luck, but by listening to the metal and letting the arc do its job.