Arc Blow in Stick Welding: Why the Arc Wanders and How to Stop It
You're running a nice bead on DC, and as you get near the end of the plate the arc starts swinging sideways or backward, spatter jumps up, and the puddle won't go where you point it. Your technique didn't suddenly fall apart. You've probably run into arc blow.
Arc blow is a magnetic effect, and once you understand where it comes from, the fixes are simple and mostly free.
What arc blow looks like
Arc blow can be subtle or dramatic. Look for:
- The arc visibly bending forward or backward along the joint, or to one side.
- A sudden increase in spatter, especially near the start or end of a weld.
- Undercut on one side and poor fusion on the other.
- Slag getting pushed ahead of the arc or into the puddle.
- Porosity, often at joint ends.
- A "hissing" or unstable arc that's normal in the middle of the plate but goes wild at the edges.
If the problem is consistently worse at the same spot on every part, such as near the ground clamp or at a corner, arc blow is the likely cause.
Why it happens
Any current flowing through a conductor creates a magnetic field around it. During welding, current flows through the electrode, across the arc, into the workpiece, and back to the ground clamp. The arc itself is a flexible conductor of hot gas, so it gets pushed around by magnetic forces in a way that solid metal doesn't.
When the work surrounds the arc evenly, the forces mostly balance. When they don't, the arc gets pushed. Common imbalances include:
Joint ends
Less metal ahead of the arc than behind it. The arc is pushed toward the heavier side.
Ground clamp position
Current path through the work concentrates the field on one side of the arc.
Corners and grooves
Uneven metal around deep root passes or inside corners.
Residual magnetism
Steel that was handled with lifting magnets or magnetically inspected.
Why DC is worse than AC
With direct current, the magnetic field builds in one steady direction. That's why arc blow is mainly a DC problem. With alternating current, the current reverses many times per second, so a strong steady field doesn't build in the same way. That's why one classic fix is to switch to AC when the electrode and machine allow it.
| Situation | Arc blow tendency |
|---|---|
| DC stick, heavy plate, near joint end | High |
| DC stick, middle of a long joint, ground well placed | Low to moderate |
| DC, root pass in a deep groove | Moderate to high |
| AC stick with an AC-capable electrode | Low |
| Magnetized pipe or plate | Can be severe regardless of technique |
Fixes, from easiest to most involved
1. Move the ground clamp
Arc blow tends to push the arc away from the ground connection. Try moving the clamp to the other end of the work, or welding toward the clamp instead of away from it, and see which reduces the deflection. Some welders use two ground connections on opposite ends of long parts to balance the field. A clamp on clean metal also matters; see our article on ground clamp contact.
Always connect the work clamp to the part being welded or the welding table it sits on. Never let welding current return through bearings, chains, hydraulic lines, building structure or other equipment.
2. Weld toward heavy tacks
Add a large tack weld at each end of the joint and some along the length. Then weld toward a heavy tack, or toward a part of the joint that's already welded. The extra metal helps balance the magnetic path. Run-on and run-off tabs at the ends of a joint serve a similar purpose on plate.
3. Shorten the arc
A shorter arc is less flexible and harder to deflect. Keep the arc as short as the electrode type allows without sticking.
4. Tilt the electrode
Angle the electrode so the tip points in the direction the arc is being blown from. In other words, lean against the blow. It won't remove the force, but it can counteract it enough to place the metal where you want.
5. Reduce current within the rod's range
The magnetic force grows with current. Dropping amperage a little, while staying in the electrode manufacturer's range, can reduce the effect. Don't drop so low that fusion suffers or the rod starts sticking.
6. Wrap the ground cable
Some welders wrap the work cable a few turns around the part to create an opposing field. Results vary and it's not a first-choice fix; it's mentioned here because you'll hear about it. If you try it, make sure the cable insulation is undamaged and isn't sitting where it will be hit by spatter or heat.
7. Switch to AC
If your machine has AC output and you're using an electrode designed for AC, this is often the most effective fix. Check the electrode box: many popular rods are rated for AC and DC, some are DC only. Our guide to inverter vs transformer welders covers which machines typically offer AC stick.
8. Demagnetize the part
For pipe or parts carrying residual magnetism, the field can be strong enough that technique changes don't help. Industrial shops use degaussing equipment for this. For hobby work, it's rare, but it's worth knowing that a magnetized part will act differently.
Practice test
Want to see arc blow and learn to handle it? Try this on scrap:
- Clamp the ground at one end of a piece of thick flat bar.
- Run a bead on DC away from the clamp and watch the arc near the far end.
- Move the clamp to the other end and run another bead in the same direction. Compare.
- Add a heavy tack at the end and weld toward it. Compare again.
- If your machine and rod support it, repeat on AC.
A wandering arc can also be caused by a damaged electrode with flux missing on one side (flux "fingernailing"), wind blowing away shielding outdoors, or a loose ground. If the problem doesn't change with ground position or joint location, check those first.
Verdict: For most hobby stick welders, moving the ground clamp and welding toward a heavy tack solves arc blow. Keep a short arc, lean the rod against the blow, and save AC for when nothing else works.
FAQ
What is arc blow in welding?
Arc blow is the deflection of the welding arc from its intended path by magnetic forces. The current flowing through the work and cable creates a magnetic field, and when that field is uneven around the arc, it pushes the arc to one side.
Why does arc blow happen at the end of a joint?
Near the end of a plate, the magnetic field is no longer balanced on both sides of the arc because there's less metal ahead of it. The imbalance pushes the arc, typically back toward the bulk of the work.
Does AC eliminate arc blow?
AC greatly reduces it because the constantly reversing current doesn't build a steady magnetic field. Only use AC with electrodes designed for AC and if your machine provides AC output.
Can a magnetized part cause arc blow?
Yes. Parts that were lifted with a magnet, sat near a strong magnetic source, or were magnetic-particle inspected can carry residual magnetism. Demagnetizing may be needed for critical work.
Summary
Arc blow isn't a mystery or a skill failure. It's magnetism, and you can usually beat it by moving the ground, tacking heavily, welding toward the tacks, keeping a short arc and tilting the rod. If all else fails and your setup allows it, AC usually ends it.
More stick reading: choosing between 7018, 6011 and 6013 and fixing common weld defects.