What Does a Good MIG Weld Look Like? A Complete Visual Guide to Reading Your Bead

Table of Contents

Introduction: Why the Appearance of a MIG Weld Tells a Story

The moment is familiar to every new welder. You lay down a bead, flip up your helmet, and stare at the cooling metal. It looks… fine? Not obviously broken, not clearly beautiful. Then the shop lead walks past, glances for half a second, and says, “Do that again.” You have no idea what they saw, and that gap in your eye is exactly what this guide closes.

Here is the truth experienced welders know: a bead is a written record. Every time your hand moved, every dip in voltage, every time your gas flow drifted, the metal kept score. Weld appearance is not vanity; it is diagnosis. The shape of the crown, the spacing of the ripples, the way the toes blend into the base metal, the amount of spatter scattered around the joint: each is a clue pointing to heat input, travel speed, wire feed speed, shielding gas coverage, and steadiness of technique.

MIG welding is technically called gas metal arc welding (GMAW), and it earned its place as one of the most widely used processes in fabrication, automotive repair, shipbuilding, and structural steel for good reason: it is fast, it deposits metal quickly, and it is comparatively easy to learn. That ease is a trap, though. Because GMAW hides so much of its behavior behind a smooth surface, beginners tend to judge a weld by appearance alone.

Quick Note: A weld bead is simply the result of one pass of filler metal laid into a joint. Its size, shape, and uniformity are among the strongest visual indicators of quality, which is why learning to read them pays off so fast.

According to MillerWelds, a good bead should be slightly crowned, with toes flowing smoothly into the base metal, consistent width and height, and no craters or voids. That single sentence is the foundation for everything else in this article.

So let’s be clear about what we’re covering. You will learn the eight visual signatures that separate a sound MIG weld from a suspect one, how width, crown, and ripple pattern reveal your settings, and what penetration and fusion look like (and why they hide below the surface). We’ll break down the classic defects, such as porosity, undercut, cold lap, burn-through, and spatter, and explain how position and base material change what “good” even means. From there we’ll move through joint types, the acceptance criteria in AWS D1.1 and B1.11, and a practice roadmap to build your eye.

But first, the caveat that keeps honest welders humble. A beautiful bead does not guarantee a strong joint. A weld can look clean on the outside and still fail if it lacks proper penetration or internal fusion. Appearance is a confidence indicator, not proof of integrity. Visual inspection is necessary, but never sufficient on its own.

Professionals lean on a simple shop self-test to close that gap: clamp the welded part in a vise and bend it. If the joint is sound, the base metal beside the weld should tear before the weld itself gives way. That is what “good” really means underneath the pretty surface.

Throughout this guide we’ll point you to deeper resources on the site, including our breakdown of good and bad MIG welds, a how to use a wire welder beginner’s guide, and our welding practice roadmap. For now, let’s learn to read the metal.

Anatomy of a Good MIG Weld: The Eight Visual Signatures

Reading a MIG bead is like reading the arc’s story. Each visual cue reveals whether travel speed, voltage, wire feed, technique, and gas coverage worked together. To judge quality quickly, focus on these eight signatures that define a sound, consistent weld.

1) Straightness and Centering

A good bead follows the joint without wandering and stays a consistent width along its length. On a fillet weld, it remains centered between the two plates rather than favoring one side. Wandering often points to poor torch control or an unstable stance, while centering issues usually stem from uneven travel angle or heat imbalance. As Wiley Metal notes, uniformity and straightness are hallmarks of a controlled process.

2) Uniform Width

The bead width should remain constant from start to finish. Narrowing and widening signal inconsistent travel speed or arc length. Uniform width shows the arc energy stayed steady, meaning your settings and hand movement were synchronized. For more on dialing in consistency, see Contact Tip Welding and How to Use a Wire Welder.

3) Smooth, Slightly Convex Contour

A good profile is flat to slightly convex, not deeply concave or excessively crowned (ropey). The Wiley Metal definition of a smooth contour means the bead rises gently above the base metal without sharp peaks. Ropey crowning — a high, rounded bead with tight, rope-like ripples — often comes from too low voltage, too fast travel, or poor technique. This shape provides throat reinforcement while avoiding stress risers.

4) Even Ripples (Freeze Lines)

Look for smooth, evenly spaced ripples that feather into the base metal at the toes. Jagged, chaotic, or widely spaced ripples signal inconsistent travel speed or arc length. These ripples reflect the solidified weld pool front, so consistent spacing means arc energy input remained balanced along the joint.

5) Feathered Toe Transition

The toe — where the weld edge meets the base metal — should flow gradually, not drop off abruptly. Steep or near-vertical bead sides mean the bead is higher and narrower than necessary, often due to excessive wire feed, low voltage, or both. Poor toe blending increases the risk of undercut and can act as a notch under load. For visual examples, compare against Good and Bad MIG Welds.

6) Minimal Spatter

Spatter around the bead should be light. Excessive spatter usually means the arc is too short (voltage low relative to wire feed), improper shielding, or contamination. Minimal spatter indicates wire feed and voltage are in the optimal range and gas coverage is effective. For shielding considerations, see Gasless MIG Welding differences.

7) No Visible Defects

A good MIG weld shows no cracks, porosity, undercut, or other surface discontinuities. These flaws compromise strength and signal deeper problems. Miller emphasizes that visible surface quality often correlates with internal soundness.

8) Evidence of Fusion at Both Edges

Fusion means the weld metal properly bonded to both base metal faces. Visually, the bead should wet into the parent metal with no sharp line of demarcation and no cold lap (where weld sits on top without fusing). Poor fusion can look like the bead “floating” on one edge — often from the wrong angle, insufficient heat, or contamination. This makes technique and settings critical for the joint.

Quick Note: For gas-shielded MIG, a push (forehand) technique lays the gas blanket ahead of the arc and helps produce a cleaner, smoother bead. This is a practical detail that improves many of the signatures above.

Stringer vs Weave Beads and Ripple Patterns

A stringer bead is a straight pass with minimal side-to-side motion, producing tighter, more uniform ripples. It’s often preferred for root passes, thin materials, and code work where a smooth profile is desired. A weave bead uses side-to-side oscillation to widen the bead and control heat input, creating broader, undulating ripples to fill wider joints faster. Both can be sound if done properly, but ripple spacing and contour must remain even.

Stack of Dimes Misconception

The “stack of dimes” look — distinct, raised ridges — is aesthetic, not a quality marker. In many structural and industrial codes, a smooth stringer bead with even ripples is preferred over exaggerated dimes. Travel speed and technique influence this effect, but what matters most is consistency, fusion, and the absence of defects. This aligns with Wiley Metal guidance on uniform, smooth contours.

Reading the Bead: What Width, Crown, and Ripples Reveal About Your Settings

Every bead is a readout of your machine settings and your hands. Once you stop judging welds as “good” or “ugly” and start asking “what does this shape tell me?”, troubleshooting becomes fast and logical.

Voltage vs. Wire Feed Speed: The Two Knobs That Talk to Each Other

On a constant-voltage (CV) MIG machine, voltage sets the arc length while wire feed speed (WFS) sets the current. Amperage follows WFS: crank the wire speed and the machine pushes more current to melt the extra wire. Think of voltage as the shape knob and WFS as the power knob.

Too much voltage gives poor arc control, inconsistent penetration, and a turbulent, wandering pool. Too little voltage causes excessive spatter, a convex bead, and weak tie-in at the toes. When the two knobs are mismatched, the weld tells on you instantly — a sputtering, popping arc that Miller’s defect guide traces straight back to this imbalance.

What Bead Profile Is Telling You

A wide, flat, or concave (sunken) bead points to too much heat, excessive voltage, or traveling too fast. A narrow, tall, ropey (convex) bead with poor tie-in means the setup is running too cold for the material thickness, so increase voltage or slow your travel speed. If the bead is excessively wide with burn-through or distortion, WFS and amperage are set too high.

The crown is simply the height of the bead above the plate. A slightly crowned bead with good toe wetting is healthy. A crown so tall its edges look like they are sitting on the surface means the puddle never fused at the edges — a classic cold-lap warning. Ripples are your travel-speed fingerprint: even, closely spaced ripples that tie smoothly into both toes signal steady speed. Wide, irregular ripples with deep valleys usually mean you are rushing or running too much voltage.

What you see	Likely cause	Fix
Convex, ropey bead, poor tie-in	Running too cold: low voltage, WFS too fast for voltage, bad ground, travel too fast	Raise voltage slightly, slow travel, check the work clamp
Wide, flat, or concave bead	Too much heat: excessive voltage, travel too fast, or too slow	Lower voltage, then tune travel speed
Excessively wide bead, burn-through	WFS/amperage too high	Reduce WFS in small steps
Heavy spatter, rough arc	Voltage too low	Increase voltage gradually
Ragged, wandering, unstable arc	Voltage too high	Lower voltage

Arc Position, Travel Speed, and Stickout

Keep the arc on the leading edge of the puddle, where the metal is still molten and wetting into the joint. Let the arc push the puddle rather than ride on top of it. Hold a consistent 3/8 to 1/2 inch of stickout for short arc; too much drops arc voltage and leaves a ropey, cold bead, while too little overheats the tip. A clean, correctly sized contact tip keeps the arc stable, so replace it as it wears.

Adjusting gun angle by just 5–10 degrees can significantly improve penetration and bead shape on the same settings. A slight push or drag changes how the arc digs in, so test both on scrap before committing.

Listen to the Arc

Your ears diagnose transfer mode before your eyes do. Short arc should sound like crisp bacon frying. Spray transfer is a smooth, steady buzz or hum with almost no spatter. A popping, sputtering sound means voltage and WFS are fighting each other.

Quick Note: Change one variable at a time. Bump voltage in half-volt steps, run a bead, then look. Chasing two knobs at once turns a two-minute fix into an afternoon.

Bead reading is a skill you build with deliberate practice, not luck. If you want a structured starting point for dialing in wire, gas, and travel, our guide on how to use a wire welder walks through the full setup. Get the settings close, then trust your eyes and ears to close the gap.

Looking Beyond the Surface: Penetration and Fusion You Cannot See

A bead can look like a museum piece and still be junk. The most dangerous MIG defects — lack of fusion, incomplete penetration, and internal porosity — hide beneath a smooth, ripple-perfect cap. That’s why a welder who only trusts their eyes is working half-blind. Start with our good and bad MIG welds guide to fix what you can see, then use the checks below for what you can’t.

What Proper Penetration Actually Means

Penetration is how deep the molten metal reaches into the joint. In a butt weld, the weld should extend completely through the material but not beyond — the fuse line reaches the root without a heavy drip hanging underneath. Excessive bleed-through is its own defect, not a sign of strength.

In a fillet weld, penetration means fusion into the root of the corner, not just a triangle sitting on the surface. On a root pass, penetration means the arc has melted both plate faces down to the joint’s bottom edge, giving you a full-thickness root that the fill passes can build on.

You can’t measure any of this with a helmet up. “Measuring” penetration means cutting a coupon and looking at it. A macro-etch test slices through the weld, polishes the face, and etches it with acid; the cross-section reveals exactly how deep fusion reached. In the field, the faster checks are the bend test and break test.

Bend test: A coupon is bent over a radius. Sound fusion stretches and holds; lack of fusion or cold lap cracks open at the joint line.
Break test: The weld is loaded until it snaps. You then inspect the fracture face for un-melted edges and internal porosity.

Quick Note: A clean cross-section never lies. Cut and etch a few practice coupons — the truth is in the slice, not the surface.

Lack of Fusion vs. Cold Lap

People use these terms interchangeably, but they’re slightly different animals. Lack of fusion is the result of weld metal failing to fuse to the base metal or to the preceding bead; improper gun angle and incorrect travel speed are primary causes. The arc simply doesn’t deliver enough heat to the sidewall.

Cold lap is a cousin. It causes the weld to overfill and overlap at the toes without true fusion — often it passes a visual check but fails a bend test. The arc rides ahead of the puddle, laying hot metal against relatively cold parent metal, and the two never truly become one.

Why does fusion fail? Low heat input, a wrong travel angle that points the arc away from the joint, or the arc running ahead of the puddle. Too-fast travel starves the puddle of heat; too-slow travel can pile metal without burning in at the toes. Research into incomplete-fusion interfaces found that oxides, voids, and carbon made up the main constituents of those boundaries, with the oxides containing silicon and manganese.

Cold lap defects can be dangerously small — averaging only 0.05–0.3 mm, according to Chalmers University research on tandem arc MAG welding — which is exactly why they slip past conventional NDT tools.

Contamination: The Hidden Porosity Factory

MIG cannot burn through rust, paint, oil, or mill scale. Those contaminants don’t vanish at arc temperature; they vaporize and get trapped as gas pockets inside the solidifying metal, leaving porosity you’ll never see from the outside. Internal porosity has many parents: a kinked liner or slipping drive rolls causing erratic wire feed, moisture in the shielding gas lines, a dirty nozzle, or oily filler wire. Each introduces gas that hardens into voids the bead hides. Clean to bright metal before you strike an arc.

Here’s the payoff: when fusion and penetration are right, a properly sized MIG weld is stronger than the parent metal around it. A correct tensile test should fail in the base plate, not in the weld. That’s the real target — not just a pretty bead.

Bad MIG Welds Up Close: Porosity, Undercut, Cold Lap, Burn-Through, and Spatter

Reject-worthy beads rarely look dramatically wrong from across the shop. What matters are small tells: a pinhole cluster here, a melted groove along a toe there. Learn each defect’s appearance, its cause, and its fix, and you can catch trouble before it ever reaches inspection.

Porosity: The Pinhole Problem

Porosity is the most common MIG defect: gas trapped in the weld metal as it solidifies, leaving tiny pinholes or bubbles scattered across or clustered on the bead. Inadequate shielding gas coverage is a leading culprit.

To fight it, MillerWelds recommends extending the wire no more than 1/2 inch past the nozzle, using a large enough nozzle, keeping that nozzle free of spatter, and following the manufacturer’s contact-tip recess recommendation. Dirty base metal, contaminated wire, wind, and excessive stickout make it worse.

Undercut: The Groove Along the Toe

Undercut shows as a narrow groove or notch melted into the base metal along the toes of the bead. Excessive voltage or current, too long an arc, a poor work angle, and travel speed that outraces the puddle all burn the edges back without filling them. Drop the voltage, tighten the arc, adjust your angle toward the side, and let the puddle catch up. Undercut is easy to miss on a first pass, so run a fingernail along the toe.

Cold Lap (Lack of Fusion)

Cold lap, or lack of fusion, is weld metal sitting on top of base metal without actually bonding. It can look deceptively smooth, “laid on” rather than blended, with the toe meeting the plate at a sharp angle. Low heat, too-fast travel, and the wrong angle starve the joint of fusion. This one cannot be dressed over: you must grind back to clean base metal, correct voltage and travel speed, verify your angle, and re-weld. Never weld over a cold lap.

Burn-Through: When the Arc Punches a Hole

Burn-through is an actual hole or blown-out crater where the arc punches clean through the plate. It is especially common on material thinner than 1/8 inch, roughly 12 gauge, because heat builds faster than the metal can absorb it. Reduce your voltage or wire feed speed and keep a steady travel pace. On thin gauges, stitch or backstep the weld and let the part cool between passes.

Excessive Spatter

Spatter is those little BBs of molten metal clinging around the bead. Excessive spatter usually points to voltage too low, wire feed too high, dirty base metal, contaminated wire, or excessive stickout. In short-arc transfer, the wire shorts and detaches a droplet 40 to 200 times per second; when that rhythm stutters, spatter flies. Clean the joint, shorten your stickout, and dial in voltage and wire speed together.

Craters at the End of a Bead

Craters form as a dip or hole at the end of a bead when the arc stops and the pool shrinks. That crater is a stress point that can lead to cracking, and it can become the starting point for a crack that travels the length of the bead. Re-trigger the gun briefly to fill the crater before you lift off.

Convex Crowning and Overlap

A convex, rope-like bead that humps above the joint signals travel too slow, voltage too low, or wire feed too high. The weld looks fat but has poor toe wetting, and in bad cases the bead rolls over its toe without fusing at all, a classic overlap welding defect rather than a harmless cosmetic flaw. Raise the voltage and speed up slightly to flatten the crown. Crossing beads on purpose is overlapping welding as a technique; accidental rollover is the defect.

Birdnesting and Stray Arc Strikes

A birdnest is a tangled ball of wire jammed at the drive rolls or gun. Too much or too little drive-roll tension, a kinked liner, or a clogged contact tip causes it. Stray arc strikes are those small dots and discolored marks where the arc touched down away from the joint; they create hard spots and crack risk. Always strike inside the joint or on a run-off tab.

Note: Some defects, like lack of fusion and internal porosity, run deeper than the surface. They require grinding the affected pass out completely and rewelding. Cosmetic dressing hides nothing from an inspector or a load test.

Read defects as a chain: appearance tells you what went wrong, and what went wrong tells you what to change. Fix the cause, not the symptom, and your next bead will look better before you even pull the helmet up.

Position and Material Change What ‘Good’ Means

A bead that looks textbook flat on the bench can look dead wrong the moment you tilt the part. “Good” is not one fixed picture. It is a moving target set by gravity and by the metal you are melting, so you have to read the weld in front of you rather than a photo in a book. The same travel speed, angle, and settings that produce a flawless bead in one position can leave a mess in another.

Gravity Rewrites the Rulebook by Position

Weld positions carry standard numbers: 1F/1G (flat), 2F/2G (horizontal), 3F/3G (vertical), and 4F/4G (overhead). Each asks the puddle to behave differently, so the target appearance shifts with every one. Learn the numbers and you stop fighting physics you cannot see.

Flat (1F/1G): gravity helps you. The puddle sits still, ripples flow evenly, and the bead can be widest here. Most “perfect weld” photos come from this position.
Horizontal (2F/2G): the puddle sags toward the lower plate. A good bead has a slightly convex crown, a crisp upper toe line, and no undercut along the top edge.
Vertical (3F/3G): the puddle fights you. Vertical-up pushes molten metal uphill; vertical-down travels faster but bites shallower.
Overhead (4F/4G): gravity is now the enemy. You need a smaller puddle and a faster freeze so metal does not drip.

Vertical-up on a T-joint is a useful benchmark for real skill. Welding it correctly requires a tighter arc, slightly reduced voltage, and a controlled weave or a stringer bead depending on plate thickness. A weave ties both sides of the joint together on thicker material; a quick stringer runs cleaner on thin steel, where extra heat only invites burn-through.

Overhead demands the opposite instinct: lower current, less wire, and shorter dwell time so the puddle solidifies before it falls. If your overhead bead sags into a fat, lumpy rope, your puddle was too large or too hot. Ease off and let the metal freeze between short, deliberate steps.

Quick Note: Before blaming your hands, check the machine. Many “position problems” are really setting problems, and our beginner’s guide to using a wire welder walks through dialing in voltage and wire speed first.

Material Changes the Color and the Risk

Mild steel is the most forgiving material you can weld. A good bead appears gray-silver once cooled, with minimal scaling or discoloration near the bead when gas coverage is correct. A light tan or faint blue tint at the toes usually means too much heat or too little shielding gas. That said, even mild steel shows its settings through the toes of the bead.

Stainless tells a story through color. A clean straw-gold or light blue heat tint is normal; dark blue, gray, or black means the metal got too hot or lost shielding and the chrome is starting to burn out. Sugaring on the back of a stainless weld is a clear sign of oxidation and lost corrosion resistance.

Aluminum is the wildcard. It conducts heat about six times faster than steel and has a low melting point, making it extremely susceptible to warping and burn-through. A good aluminum bead tends to look brighter, wider, and flatter than steel, with a fine, frosty ripple pattern. That glossy surface also hides just how fast the puddle can drop through, so watch the pool, not the shine.

But aluminum punishes mistakes fast. It wears a tough oxide layer that melts at a far higher temperature than the metal underneath, so the arc has to cut through it first. Craters at the end of a weld are a common MIG defect and must be filled or they create a stress point that can lead to cracking. You also get smut, a black sooty film, plus blow-through when travel speed or heat is off.

Aluminum wire has less tensile strength than steel wire, causing feeding issues (birdnesting) unless the correct liner, drive rolls, and a spool gun or push-pull system are used. Knowing what is inside your wire helps — see what MIG welding wire is made of — and for the arc side, our guide to DC welding aluminium explains how polarity changes the game entirely.

Good Welds by Joint Type: Butt, T-Fillet, Lap, and Root Passes

A good bead isn’t universal. The same arc, wire, and travel speed that produces a perfect T-fillet will leave a butt joint looking wrong, and vice versa. Each joint geometry loads the metal differently, so “good” changes with the setup. Here’s what to look for at each one.

Butt Joints: A Slightly Raised Bead, Centered

On flat mild steel, a well-made butt weld sits as a slightly raised bead centered over the gap, with fusion lines visible on both plates. The edges should wet in smoothly, with no deep trench where the bead meets the parent metal. If the weld sinks below the surface, you have underfill, and the usual culprits are traveling too fast or running voltage too low.

T-Fillets: Equal Legs, Centered in the Corner

Fillet welds make up most MIG work, and the visual rules are simple. A good fillet sits centered between the plates with equal legs and a slightly convex face. When the bead covers more of one plate than the other, you have created asymmetry, a lopsided weld that pushes load through an uneven path and concentrates stress on one side. Watch for overlap too, where the toes roll over the base metal instead of fusing into it.

Lap Joints: Flat and Blended, No Rollover

A good lap weld fuses into both the top edge of the lower plate and the face of the upper plate, blending cleanly into both surfaces. Cold lap, where the puddle rides on top without melting in, and rollover are the failure modes to hunt for. Both hide under an otherwise decent-looking bead, so watch the puddle wet in as you go, not just the finished profile. Fit-up drives all of this: gaps and mismatched edges wreck the best technique, whether you are welding tubular joints with weld tube fittings or a simple lap. When reworking automotive sheet, drilling out old spots with a spot weld cutter bit gives you clean surfaces to re-fuse.

Root Passes: Full Penetration, Controlled Reinforcement

Root passes are judged from both sides. You want consistent reinforcement, a uniform crown on the back, without excessive bleed-through that creates a lumpy inner surface. Full root penetration is the goal; a root that only kisses the surface will fail under load no matter how pretty the cap looks.

Corner and Edge Joints

Corner joints need enough deposit to round the corner without leaving a deep valley at the toe. Edge joints, two parallel sheet edges, want a bead that ties both edges together without dropping through. MIG is forgiving here, but if the puddle falls through, the joint is too wide or your heat is too high.

Checking Fillet Leg Size

For fillets, leg size is a specification, not a guess. A fillet gauge, the stepped leaf-style tool, measures both legs quickly. Slide it against the weld; the correct leg length touches the toe on both plates. Unequal readings mean asymmetry, and that is a repair, not a pass. Remember that a fillet’s penetration cannot be seen from the outside at all. That is why procedure qualification uses macro-etch specimens, cutting and polishing a cross-section to reveal how deep fusion actually reached.

Quick Note: AWS D1.1 requires all weld crater cross-sections to be filled to provide the specified weld size, except at the ends of intermittent fillet welds outside their effective length. Do not stop your arc and leave a hollow crater.

Surface appearance gets you most of the way, but it will not confirm fusion. For defects you can measure, Miller’s weld defect troubleshooting guide maps each flaw to its likely cause, from travel angle to wire feed speed.

Visual Inspection Standards: What AWS D1.1 and AWS B1.11 Actually Require

“Looks good to me” has never held up on a bridge, in a pressure vessel, or in front of a paying customer. That’s exactly why welding codes exist. They take the fuzzy judgment of an experienced eye and convert it into measurable numbers — depths, lengths, diameters — so two inspectors studying the same bead reach the same verdict. For MIG work, two documents do most of the heavy lifting: AWS D1.1, the Structural Welding Code—Steel, and AWS B1.11, the Guide for the Visual Inspection of Welds.

Two Documents, Two Jobs

AWS D1.1 is the rulebook of acceptance criteria: it tells you what passes and what gets rejected. AWS B1.11 is the procedure manual — how to hold your light, what magnification and illumination to use, and how to conduct a proper examination. One sets the bar, the other shows you how to measure against it. Confusing them is common, but the distinction matters when a customer asks why a weld you thought looked fine got tagged.

Discontinuity vs. Defect

Welders use these words loosely, but codes are precise. A discontinuity is any interruption in the weld’s uniformity — undercut, porosity, a lumpy toe. A defect is a discontinuity that exceeds the acceptance limits and must be repaired. The same 1/32-inch undercut might be perfectly fine on one joint and rejectable on another. Severity decides which word applies, not existence.

The Hard Limits Worth Memorizing

Here is where D1.1 stops being vague:

Cracks: any crack shall be unacceptable, regardless of size or location. No exceptions, no argument.
Undercut: for material less than 1 inch (25 mm) thick, undercut is limited to 1/32 inch (1 mm) in depth. An exception allows 1/16 inch (2 mm) for an accumulated length up to 2 inches in any 12 inches of weld. On material 1 inch and thicker, undercut shall not exceed 1/16 inch (2 mm).
Porosity: for fillet and most groove welds, the sum of visible piping porosity 1/32 inch (1 mm) or greater in diameter shall not exceed 3/8 inch (10 mm) in any linear inch of weld and 3/4 inch (20 mm) in any 12-inch length. In fillet welds, the frequency shall not exceed one in each 4 inches (100 mm), with a maximum diameter of 3/32 inch (2.5 mm).
Undersized welds and craters: fillets must meet the specified leg size, and craters must be filled to the full cross-section of the weld.

When Visual Inspection Can Happen

Visual inspection of welds in all steels may begin immediately after the completed welds have cooled to ambient temperature. But for ASTM A514, A517, and A709 Grade 100 steels, it must be performed not less than 48 hours after completion. Those high-strength grades are prone to delayed cracking, and waiting is the cheapest test you will ever run.

ISO 5817 and Quality Levels

Outside the US, or on internationally specified work, ISO 5817 assigns quality levels B, C, and D to fusion-welded joints, each with its own imperfection limits. Level B is the most stringent, D the most permissive. The philosophy is identical — quantify the flaw — just expressed on a different scale.

Quick Note: 100% visual inspection is standard on most structural work — before, during, and after welding. It is the only inspection method applied to every inch of a joint, but the weld must be clean and free of slag, spatter, and dirt before anyone judges it.

Codes exist so “looks good to me” becomes measurable. To sharpen your own eye against these limits, work through our guide to building real welding skills, then compare your beads side by side using our breakdown of good and bad MIG welds.

The Ten Most Common Beginner Mistakes (and Exactly How to Fix Them)

Almost every ugly MIG bead traces back to a short list of habits, and the fix for most of them is the same discipline: change one variable at a time and watch what the bead does. Twist the voltage and travel speed together and you learn nothing. Move one thing, run a bead, compare. That loop is how you build real diagnostic instinct instead of guessing.

Start With the Ground Clamp, Always

If your arc sputters, wanders, or the weld looks cold despite sensible settings, don’t reach for the dials. Check the work clamp first. A poor-quality or badly placed ground clamp causes erratic arcs and cold-looking welds. Use a copper clamp, bite it onto clean bare metal, and keep it close to the joint. Paint, rust, and mill scale under the clamp add resistance that masquerades as a machine fault.

Quick Note: Erratic, cold-looking welds even with good settings should prompt a check of the work clamp connection before you adjust anything else.

Stickout and Gun Angle

Keep stickout between 3/8 and 1/2 inch. Welding too close increases current and risks burn-through; too much stickout reduces shielding and invites porosity. A travel angle of 5–15 degrees helps eliminate defects including porosity, while angles beyond 20 degrees pull the nozzle too far away and expose the molten pool to air. That single angle habit fixes more beads than any gadget.

Travel Speed, Voltage, and Cleanliness

Rushing drags the bead thin and ropey; crawling piles metal up and burns through thin sheet. Voltage sets arc length. Too little gives a tall, humped crown; too much flattens and widens it. Dirty base metal is another classic culprit. A plating or primer under the weld is a known root cause of internal porosity, so grind to bright metal before you strike an arc.

Shielding Gas, Wind, and Contaminants

Wind or a draft blows shielding gas away and causes porosity even when the metal looks perfectly clean. Block the airflow or switch to self-shielded flux-cored wire. Humid gas cylinders and a kinked or worn liner cause similar trouble. Excessive anti-spatter gel burns off in the gas stream and becomes a contaminant that leads to porosity, so use it sparingly. A damaged liner or contact tip also produces erratic feeding and arc wander, which is why inspecting them belongs in routine maintenance.

Use Your Ears: The Good Sound

A correct MIG arc makes a steady, frying-bacon sizzle. Popping, crackling, or a harsh hiss means something is off, usually stickout, gas coverage, or wire-feed trouble. Your ears catch problems your eyes miss, and the tone shifts the instant a variable goes wrong. Treat the sound as a live readout.

Cause-to-Fix Cheat Sheet

Mistake	What You See	The Fix
Bad ground clamp placement	Erratic arc, cold weld	Copper clamp on clean bare metal, close to joint
Stickout too short	Burn-through	Hold 3/8–1/2 inch
Stickout too long	Porosity	Move nozzle closer to work
Poor gun angle	Porosity, uneven bead	Keep 5–15 degrees travel angle
Wrong travel speed	Ropey or humped bead	Steady drag, match ripple spacing
Wrong voltage	Flat/wide or tall crown	Adjust arc length one step at a time
Dirty metal or primer	Internal porosity	Grind to bright metal
Draft on gas	Porosity on clean metal	Block wind or go flux-cored
Anti-spatter overuse	Contamination, porosity	Use sparingly, wipe excess
Unfilled crater	Crater crack	Pause and fill before stopping

Two Habits That Ruin Otherwise Good Beads

First, never stop without filling the crater; an unfilled crater cracks under load. Second, know your process. If you run gasless wire, confirm your polarity for flux core is correct, and remember that flux core isn’t the same as MIG in setup or troubleshooting. Manufacturers publish useful defect charts worth bookmarking, like Miller’s troubleshooting weld defects guide and Lincoln’s MIG problems and remedies page.

Change one variable, listen, look, and log the result. Ten mistakes feel overwhelming until you realize they collapse into a simple rhythm: check the ground, mind the stickout and angle, keep it clean, shield it from wind, and finish the crater. Do that and your beads start reading like good sentences.

Building the Eye: A Practice Roadmap and Final Checklist

Reading a MIG bead is a learnable skill, not a talent you are born with. It develops through deliberate, structured practice rather than guesswork, and the more coupons you run, the sharper your eye becomes. Watch as instructors at welding schools such as Tulsa Welding School demonstrate good beads, then compare your own work to that reference. That side-by-side calibration is how you train yourself to spot subtle differences in contour, ripple spacing, and toe blending. The goal is not perfection in a single pass, but steady, consistent improvement across joints and positions until the visual signs reliably reflect sound fusion and proper settings.

Practice Roadmap

Start with simple exercises and build complexity gradually. Begin with straight pad beads on flat plate to develop rhythm, torch angle, and travel control, then progress to T-fillets, vertical-up, lap joints, and finally butt joints. This sequence, emphasized in Welding Practice, mirrors the way real shop work layers difficulty, so skills transfer instead of collapsing under pressure. For every coupon, photograph and date it, and keep a detailed weld log of voltage, wire feed speed, gas flow, and your observations. Change only one variable at a time so you can clearly attribute bead changes to specific settings, a disciplined approach recommended by Miller. Over weeks, that one-variable discipline builds a mental map of cause and effect that no chart can replace.

Pay attention to sound as well as sight. A steady buzz or hum paired with good bead appearance often indicates spray transfer at higher voltage and wire feed on thicker material with the proper gas mix, while a harsh crackle usually signals short-circuit transfer or settings that need adjustment. Work in a clean, organized area with proper ventilation and Protective Eyewear for Welding, and make sure your Welding Facilities support safe, repeatable practice with good lighting and comfortable positioning. To connect surface appearance to what lies beneath, section (cut, polish, and etch) practice coupons using a macro-etch; this standard method reveals penetration and fusion geometry behind the bead, as outlined in AWS B1.11.

Quick Note: Good habits compound. Photographing every coupon and logging settings turns random passes into data you can analyze and improve.

Final Checklist

Before you call a weld “good,” verify these visual and practical points. A sound MIG bead is straight, flat to slightly convex, uniform in width, and free of undercut, overlap, porosity, and cracks, with minimal spatter and no black soot — characteristics described by industry sources. Run through the list below on every coupon, and treat it as a habit rather than a hurdle; with repetition, the checks become second nature.

Straightness and consistent travel along the joint
Uniform width with even ripples along the length
Smooth contour (flat to slightly convex crown)
Feathered toes blending smoothly into base metal
Minimal spatter and no black soot
No visible defects: no undercut, overlap, porosity, or cracks
Confirmed fusion at toes and consistent tie-in
Sound matches appearance and settings are documented

Closing

Consistently producing welds that meet these criteria takes deliberate practice and attention to detail. There are no shortcuts, but the payoff is a reliable eye you can trust in the shop. By following a structured roadmap and using this checklist, you train yourself to read the story in every bead. As you compare your work to the examples in Good and Bad MIG Welds, remember the core message: reading a bead is a learnable skill. The welder with the sharpest eye is usually the one who has run the most coupons. The visual signs you see — contour, width, ripples, toes, spatter, and absence of defects — are direct reflections of process variables like voltage, wire feed speed, travel speed, stickout, gas mix, and technique; mastering those variables, one at a time, is what makes the bead look right.

Frequently Asked Questions

What does a good MIG weld look like in one sentence?

A good MIG weld is a straight, uniform bead that is flat to slightly convex, with smooth evenly spaced ripples, toes that flow gradually into the base metal, minimal spatter, and no visible porosity, undercut, cracks, or craters.

Can a MIG weld look good but still be bad?

Yes. A bead can have a flawless surface while hiding lack of fusion, cold lap, or internal porosity. This is why appearance creates confidence but cannot replace bend tests, sectioning, or nondestructive examination on critical joints.

Is a ‘stack of dimes’ pattern a sign of a good MIG weld?

Not necessarily. The ridged, stacked-dimes look comes from a specific weave motion and is largely cosmetic. A smooth, consistent stringer bead can be just as strong or stronger, and many codes care about contour and defect-free toes rather than ripple aesthetics.

Why is my MIG bead tall and narrow (ropy)?

A tall, narrow, crowning bead usually means the weld is running too cold — voltage is too low for the wire feed speed, travel speed is too fast, or the work clamp has a poor connection. Increase voltage one step, then slow the travel speed slightly if needed.

What causes small holes in the surface of a MIG weld?

Those are porosity, caused by gas trapped in the solidifying weld pool. Common culprits are inadequate shielding gas coverage, dirty or oily base metal, excessive stickout, wind blowing the gas away, a clogged nozzle or contact tip, and contaminated or wet gas cylinders.

How much undercut is acceptable on a MIG weld?

Under AWS D1.1, for material under 1 inch thick, undercut generally may not exceed 1/32 inch (1 mm) in depth, with a limited exception of 1/16 inch (2 mm) for up to 2 inches of length in any 12 inches of weld. For material 1 inch and thicker, the limit is 1/16 inch.

What stickout and travel angle should I use for clean MIG welds?

Keep wire stickout between about 3/8 and 1/2 inch and use a travel angle of roughly 5 to 15 degrees. Excessive stickout and steep angles pull the nozzle too far from the pool, weakening gas coverage and inviting porosity and spatter.

How do I know if my MIG weld has good penetration?

You cannot reliably judge penetration from the surface alone. Use a bend test — the base metal next to the weld should fail before the weld does — or weld a practice coupon, cut it across the joint, polish it, and etch it to reveal actual penetration and fusion.