Troubleshooting guide › Weld defects › Bad bead shape
The shape of the bead is the welding machine talking to you. Too high and narrow means cold; too wide and flat means hot or slow; ropey means the voltage is wrong; uneven means the hand or the feed is uneven. Reading the bead correctly is the fastest way to set a machine, and most of the other defects on this guide announce themselves through bead shape first.
Reviewed by the Cruxweld technical team, October 2026. Settings are starting points to confirm on a test piece; acceptance is decided by the code or drawing the job is built to. Checks marked “call” are for our technical team.
Convex: the bead stands up like a rope with sharp toes. Concave: the fillet face is hollow and the throat is thin. Excess reinforcement: a butt weld cap more than 2-3 mm above the plate. Uneven: width and height vary along the length, or the ripples are irregular. Narrow and high: a stringer that does not wet the plate.
Illustration, not a photo. Orange marks the defect.
| What you see | What it means | Change |
|---|---|---|
| High, narrow, ropey bead with sharp toes | Voltage too low for the wire speed (MIG), current too low (stick), or travel too fast | Raise voltage one step; or raise current; or slow down |
| Wide, flat bead, maybe undercut at the edges | Voltage too high, or travel too slow with high current | Lower voltage; speed up |
| Concave fillet (hollow face) | Voltage too high, travel too fast, or welding vertical-down | Lower voltage; slow down; weld vertical-up |
| Excess reinforcement on a butt weld (cap above 3 mm) | Too much filler: travel too slow or too many passes | Faster final pass; plan the passes so the cap is 1-2 mm |
| Bead wider on one side | Torch angle biased, or arc blow | Centre the torch; move the earth clamp |
| Width changes along the length | Hand speed uneven; wire feed slipping; mains voltage swinging | Rest the torch hand; check feed rolls and liner; look at the voltmeter while welding |
| Coarse, irregular ripples | Arc length changing: stick-out varying, long arc on stick | Keep stick-out and arc length constant; brace the hand |
| Bead with a dull, grey, oxidised surface | Gas cover poor; on stainless and aluminium, too little post-flow | Check gas flow and nozzle; add post-flow |
| Bead sunk with a hole in the middle | Burn-through: too hot or too slow | See the burn-through page |
| Lumpy start, thin finish | Too much current at the start on cold plate, crater at the end | Use hot start or run-on tab; fill the crater |
On every arc process three things set the bead: how much metal goes in (current or wire speed), how wide the arc is (voltage or arc length), and how fast you move (travel speed). Change one at a time.
| Setting | Raise it and the bead gets | Lower it and the bead gets |
|---|---|---|
| Current / wire speed | Deeper penetration, bigger, more convex | Shallower, smaller, colder, may not fuse |
| Voltage / arc length | Wider, flatter, less penetration, more spatter if too high | Narrower, higher, ropey, more short-circuit spatter |
| Travel speed | Narrower, less penetration, undercut if too fast | Wider, more penetration, overlap and burn-through if too slow |
A quick rule for MIG: set wire speed for the plate thickness, then tune voltage until the arc sounds like steady frying and the bead toe wets the plate. Then set travel so the bead is 2-2.5 times the wire diameter wide on a stringer.
| Fillet weld | Flat to slightly convex face, equal legs, toe angle wide and smooth |
| Butt weld cap | Reinforcement 1-2 mm, maximum 3 mm, blending into the plate |
| Root bead (single side) | Continuous, slightly raised, 1-2 mm, no suck-back |
| Stringer bead width | About 2-2.5 times the wire or core diameter |
| Ripples | Fine, even, overlapping like fish scales |
These are visual targets for general fabrication. Codes give measured limits for reinforcement and toe angle.
No. A convex fillet has the same throat as a flat one with the same leg, but sharper toes that concentrate stress. Extra height is wasted wire.
The job is colder, dirtier, or in a different position. Scale, paint, a draught, a longer cable run or a 20-degree change of torch angle all change the bead. Test on the job material in the job position.
No more than about 2.5 times the electrode core diameter on stick, or 10-12 mm on MIG. Wider weaves cool at the edges and give overlap, undercut and slag inclusion.
A machine with readable, repeatable settings is what makes bead shape useful as a tool. Synergic MIG machines that set voltage from wire speed produce a good bead at any point on the scale; a transformer machine with a coarse tap switch sometimes cannot hit the right voltage at all for a given wire speed, and the bead stays slightly wrong.
Send a photo of the weld or cut, your machine model, consumable and plate thickness. Our technical team replies on WhatsApp with the likely causes and the next checks to make.
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