Beginner welding mistakes: twelve common ones and how to fix each
The twelve mistakes most new welders make with a wire feed machine, how to spot each one in the bead, and the single change that fixes it.
A row of lumpy, spattery beads is how nearly everyone starts. It is rarely the machine and rarely you. It is usually one of a short list of setup problems, and most take a minute to fix.
Before you touch a setting, check three things: the ground clamp is on clean bare metal close to the weld, the steel is ground bright where you are welding, and the polarity matches your wire. Those three cause most bad first welds.
The three basics
- Ground clamp. The current has to return through it. Clamped over paint, rust or scale, or on the bench across the room, it gives an unstable arc that no setting will cure.
- Clean metal. Mill scale, rust, paint and oil turn into gas and slag inside the weld. Grind until it shines.
- Polarity. Flux core and gas mig usually need opposite polarity, swapped with two leads inside the machine. The manual shows which way round. Wrong polarity gives a harsh arc and heavy spatter.
Twelve mistakes, by what you see
| What you see or hear | Likely mistake | The one change |
|---|---|---|
| Tall, ropey bead sitting on top of the plate | Too cold, or moving too fast | Set from the machine’s chart for your thickness, then slow down |
| Wide, sagging bead or a hole burned through | Too hot, or lingering | Step the voltage down one setting, or move faster |
| Heavy spatter and a crackling, harsh arc | Wrong polarity, or the wire sticking out too far | Check polarity, then hold the tip about a finger width from the work |
| Small holes in the bead | No shielding reaching the puddle, or dirty metal | Check gas flow and drafts, or polarity and dry wire for flux core. Clean the steel |
| Wire punching into the work and pushing the gun back | Wire speed too high for the voltage | Turn wire speed down a little at a time |
| Wire burning back and fusing to the contact tip | Wire speed too low, or the gun held too close | Raise wire speed slightly and hold a steady finger width |
| Wire feeding in jerks or birdnesting at the drive roll | Tension wrong, liner kinked, or tip too small | Straighten the gun cable, match tip and roll to the wire, set tension just tight enough to feed |
| Bead wanders off the line | Unsteady position, or you cannot see the joint | Brace your arm, use both hands, do a dry run, and if the shade is darker than you need, step it lighter, never below the chart minimum |
| Bead width changes along its length | Speed changing | Watch the puddle and keep it the same size |
| Weld sits on one piece of a joint and not the other | Gun aimed at one side | Split the angle between the two pieces |
| Machine stops mid-weld and a light comes on | Duty cycle reached | Leave it switched on so the fan cools it, and wait. It is a limit, not a fault |
| Breaker trips | Circuit cannot supply the machine | Turn down, remove other loads, and read the section below |
Change one thing at a time. Number your practice beads with a marker and note what you changed. Ten numbered beads teach more than fifty random ones.
Two that are about the machine’s limits, not your hands
The thermal light. Every welder can run only so many minutes in ten before it must cool. At 20 percent that is two minutes of welding and eight of waiting. It feels like a breakdown the first time. It is the machine protecting itself, and it is explained in welder duty cycle.
Tripping breakers. Many small welders sold for household outlets list input currents of 40 amps or more in their manuals, and a household circuit supplies 15 or 20. They work at lower settings and trip the breaker when turned up. We set out the numbers in welder amp draw and 110v vs 220v welders. A long or thin extension cord makes it worse: see extension cord size. Do not fit a bigger breaker to stop the tripping. The breaker protects the wire in the wall. Talk to a licensed electrician.
Mistakes that are not about the bead
- Welding in short sleeves “just for a minute”. The arc burns skin like strong sun, fast.
- No safety glasses under the helmet. Slag pops off as a weld cools, often when the helmet is up.
- Picking up the workpiece. It stays hot long after it stops glowing. Use pliers and mark hot pieces.
- Leaving right after the last weld. Sparks smolder. Stay and check.
- Judging strength by looks. A neat bead can have poor fusion underneath. Break practice joints in a vise to learn what yours are doing. For anything that carries a load, that judgment belongs to a certified welder.
If you are still setting up, how to weld walks through the first session in order.
Frequently asked questions
Why are my welds full of holes?
Small holes, called porosity, mean air reached the molten metal. With gas mig, check that the cylinder is open, the flow is set as your manual says, there is no draft, and the nozzle is not clogged with spatter. With flux core, check the polarity and that the wire is dry. With either, clean the metal to a bright finish first.
Why does my breaker trip when I weld?
The welder is asking the circuit for more current than it can supply. Many small machines list far more input current than a household circuit provides, and other loads on the same circuit make it worse. Turning the output down helps. The lasting fix is a circuit that matches the machine's manual, planned by a licensed electrician.
Is it my welder or my technique?
Usually technique or setup. Check the ground clamp, the metal preparation, the polarity and the chart settings before suspecting the machine. A machine fault tends to show as wire that feeds in jerks with the gun cable straight, an arc that cuts out, or the thermal light coming on quickly.
Can I fix a bad weld by welding over it?
Welding over a flawed bead usually traps the flaw underneath. Grind it out to clean metal and weld again. On practice pieces this is good training. On anything that matters, a flaw you cannot see is the reason that work belongs to a certified welder.