At the risk of sounding like a TV infomercial, are you struggling with undercuts? Are your weld beads crooked or wavy? Is there too much spatter around your welds? If you answer “yes” to any of these, you may be suffering from arc blow.

You can put away that credit card because there’s no 800 number to call for an arc blow solution, and no operators are standing by to take your call. What you can do though is apply a little science and logic to the problem. Here’s our not too technical explanation of why it happens, and some suggestions for what to do about it.

Causes and Symptoms

This is primarily a problem of electricity and magnetism. Electrical current generates a magnetic field around the conductor. (This is also the basis of electric motors.) The greater the current the stronger is the magnetic field.

When you begin welding and strike an arc, current flows between the torch electrode and the pieces you’re joining. (As an aside, that current is usually DC, but it doesn’t have to be.) Around that arc there’s a magnetic field.

Under normal circumstances the arc takes the shortest path, but external magnetic fields and workpiece geometry can make it wander. It’s a particular issue when the workpiece itself is magnetic. (This is why you only really see arc blow when welding steel.) Some edge and corner geometries can also alter the shape of the field around the arc.

When the arc begins wandering the welder finds he’s fighting the weld, and things get messy. Here’s what to look for:

  • Undercuts. These look like a groove in the workpiece along the edge of the weld bead. They’re bad because they create a weakness in the join.
  • Untidy beads. A pro welder strives for a bead that’s straight and uniform. Irregular width, waviness or wandering not only looks bad but may signify a poor quality join. However, when the arc wanders away from the shortest path, this is what happens.
  • Inconsistent penetration. Not easy to see, but a common result of a wandering arc.
  • Porosity. Another result of poor control over arc and weld pool position, this can severely weaken a join.
  • Excess spatter. When managing the weld pool is difficult there’s often a lot of spatter. That makes for a poor appearance and lots of clean-up.

Far less often, it is the result of poor temperature control. Local hot spots in the workpiece can alter the route taken by the arc, causing it to wander and resulting in the arc blow problems listed above.


If you’re struggling with this issue there are five things to try:

  1. Switch to AC power. Welders generally prefer DC because it makes for easier starting and there’s usually less arc wander. If you’re facing arc blow though, AC is the obvious first step. (It might mean changing the electrode to one optimized for AC.)
  2. Shorten the arc length. Not only does this reduce the distance over which the arc can wander, but it usually means reducing current, which lessens the magnetic field around the arc.
  3. Wrap the ground cable around the workpiece. The idea is that this cancels out any magnetic effects being induced.
  4. Angle the torch. If the arc is moving a consistent direction – either lagging or leading the electrode, try angling the torch to compensate.
  5. Tack Welds. Make tack welds rather than putting in one continuous bead.

But wait, there’s more!

Electricity and magnetism are inextricably linked, and that’s what’s at the heart of the issue. Like many problems though, once you understand the cause solutions seem rather obvious. Best of all,  this is one problem that doesn’t need a credit card to solve. (And that’s it. There is no more.)