A rare occurrence, but one that can drive an operator question his life's choices. You've replaced the consumables. You've ruled out the torch. The air is dry, the settings came off the chart, and the height control is behaving.
And the cut face still wanders.
At this point most shops start pulling the machine apart. Before you do, check the one thing almost nobody checks: the plate itself.
Arc blow, briefly
A plasma arc is a column of electrically conductive gas, and like any current-carrying path it responds to magnetic fields. Put a strong enough field near it and it deflects. Welders have known this for a century — they call it arc blow, and it's the reason a stick weld sometimes refuses to go where it's pointed.
The same physics applies to a plasma arc. If the plate carries significant residual magnetism, the arc gets pushed off vertical, and that shows up in your cut as wander, a wavy kerf, or an edge that won't come square no matter what you do to the settings.
The frustrating part is that everything else checks out, because everything else is fine.
Where the magnetism comes from
Steel doesn't arrive magnetized by accident as often as you'd think, but it happens more than most shops realize.
Magnetic lifting. Lift magnets and magnetic clamps are the most common source. Plate handled repeatedly with a mag lift can hold residual field long after the magnet is gone.
Magnetic particle inspection. Any plate that's been through MPI has been deliberately magnetized. It's supposed to be demagnetized afterward. It isn't always.
Storage and handling. Steel stored for long periods in one orientation can pick up a weak field from the earth alone. Cold-working, impact, and vibration during transport all contribute.
How it arrived. Some imported plate shows up already carrying field from processing or handling at origin. If you're buying on price from a source you don't know well, this is one of the things you can inherit along with the savings.
Your own ground path. A poor ground connection, or a ground clamped somewhere that forces current to take a long path through the plate, generates its own field while the machine is cutting. This one is self-inflicted and it's also the easiest to fix.
How to tell it's magnetism
The pattern is what gives it away.
It's directional. Arc deflection from a magnetic field pushes consistently one way. Cuts running in one direction come out worse than cuts running perpendicular to them. If you rotate the part on the table and the problem rotates with the plate rather than staying with the machine, that's your answer.
It follows the plate, not the machine. Cut the same program on a different plate. Clean cut means it was never the machine.
It's worse near edges and holes. Field concentrates at discontinuities, so wander often shows up worst near the plate edge, near existing holes, or at the end of a cut.
The simple test. A compass held near the plate will deflect. A paperclip or small nail will cling where it shouldn't. It's crude, and it won't tell you how much field you have, but it will tell you whether you have any — which is the question you're asking.
What to do about it
Check your ground first. It's free, it's frequently the cause, and it takes a minute. A clean, tight ground clamped close to the cut path removes a self-generated field before you go looking for an inherited one.
Change the cut direction. If wander is directional, reorienting the part on the table can move the problem out of your critical features. It's a workaround rather than a fix, but it gets a job out the door.
Demagnetize the plate. Handheld demagnetizers and degaussing coils exist for exactly this, and they're standard equipment in shops that do magnetic particle inspection. Procedure varies by tool and by plate size, so follow the equipment's instructions rather than a rule of thumb — and verify afterward rather than assuming it worked.
Fix the handling. If plate is arriving or becoming magnetized on your floor, the mag lift is the usual suspect. That may be a workflow conversation rather than a technical one.
Why this belongs at the end of the list
Magnetism is not the common cause of arc wander. Worn consumables, a tired torch, wet air, and standoff drift are all far more likely, and you should rule every one of them out first.
But it belongs on the list, because a shop that doesn't know about it has nowhere to go once the ordinary causes are exhausted. That's when the machine gets torn apart, the parts get blamed, and a supplier gets fired for a problem that came in on the truck with the steel.
The sequence is worth remembering: parts, then torch, then plate. Most of the time you never get past the first one. But when you do, keep going — there's one more layer out there than most people check.
Need parts? Our guided finder walks you from your machine and amperage to the complete stack — in assembly order, with current pricing. Find your consumables →
TorchandTip.com sells Thermacut® aftermarket plasma and welding consumables across Canada. Thermacut® is an independent manufacturer. TorchandTip.com is not affiliated with, authorized by, or endorsed by Hypertherm®, ESAB®, Lincoln Electric®, Kjellberg®, or any other original equipment manufacturer. All OEM names, model numbers, and part numbers are used for identification and reference purposes only.
0 comments