If your plasma cutter won't cut rusty or painted steel and you're standing there thinking, "What the bloody hell's wrong with this thing?", don't start pulling the torch apart just yet. I've seen blokes throw new tips, new electrodes and all sorts of parts at a plasma cutter, only to find there was bugger-all wrong with the machine.
The first thing I do is leave the plasma cutter alone and have a good look at the steel. Nine times out of ten that's where the problem is. Rust, thick paint, mill scale, a crap earth or even just where you've clamped onto the job can make a perfectly good plasma cutter cut like absolute rubbish.
Spend two minutes checking that first, and you might save yourself an hour of stuffing around chasing a fault that was never there.
The next thing I do is move the earth clamp. It sounds too simple, but I've lost count of the number of times that's fixed the problem. If you've got the earth clipped onto a rusty bit of steel a couple of metres away from where you're cutting, don't expect miracles.
I always try to get the clamp onto clean, bare steel as close to the cut as I can. The closer you can get that earth lead to where you're actually cutting, the better chance the plasma cutter has of doing its job properly.
If it still cuts like rubbish, I'll grab the grinder and clean up a small patch. I'm not talking about polishing the whole job until it looks brand new. Just clean enough steel to give the earth a decent connection and somewhere for the arc to get started properly.
If it suddenly starts cutting sweet, you've just found the problem without touching the plasma cutter.
Once I've checked the earth and cleaned a small patch, I'll try cutting a bit of clean steel. Not the rusty gate, not the painted trailer, and not that old bit of farm gear that's been sitting outside for ten years. Just a clean bit of steel.
If it cuts that nicely, you've just proved the plasma cutter is probably fine. It's telling you the problem is the job you're trying to cut, not the machine itself.
That's why I don't like jumping straight to consumables. Yes, worn consumables can make a plasma cutter cut like crap, but don't just assume that's the problem. Have a look first. I've seen plenty of blokes throw a perfectly good set of consumables in the bin because the real problem was dirty steel or a bad earth.
If you're not even sure what torch or consumables you've got, start with the plasma torch identification guide before you start ordering parts.
There's one more thing that catches a lot of people out. Not all plasma cutters are built the same. If you've got a scratch-start machine, don't expect it to cut through heavy rust, thick paint and all sorts of rubbish like a pilot arc machine will. That's just not what it was designed to do.
I actually made the same mistake myself. About fifteen years ago I bought my first plasma cutter, and like most blokes I bought the cheapest one I could find. It wasn't until about six months later that I even realised it was a scratch-start machine. To be honest, I didn't even know what a scratch-start plasma cutter was back then. I just thought that's how all plasma cutters worked.
The funny thing is, there was nothing wrong with the machine. It was actually a bloody good plasma cutter and it still works today. The problem wasn't the plasma cutter. It was me expecting it to do jobs it was never really made for.
Years ago there was a fair chunk of money between a basic scratch-start plasma cutter and a pilot arc machine. These days, especially with the cheaper Chinese plasma cutters, you're often only talking twenty or thirty bucks difference at the bottom end. For that sort of money, I'd buy the pilot arc version every time.
Where a pilot arc machine really comes into its own is dirty, awkward jobs. If you're lying under an old truck trying to cut an exhaust off, or working underneath a rusty old car, the last thing you want to do is crawl out, grab the grinder, clean a shiny patch and then crawl back underneath again.
One of my mates is a panel beater, and he bought a scratch-start plasma cutter about the same time I bought mine. He spends a lot of his time cutting rusty sections out of old classic cars. Before that he was using a grinder. It worked, but it made a hell of a mess, threw sparks everywhere and, more importantly, you can only really cut straight lines with a grinder.
Try cutting around the curve of a wheel arch or following the shape of a rusted panel with a grinder and you'll soon find its limits. A plasma cutter is a completely different animal. You can follow curves, cut around awkward shapes and take out just the rust instead of hacking away half the panel.
The biggest pain with his scratch-start machine was always getting a decent earth and somewhere clean enough for it to start properly. He'd clean a little patch where he wanted to cut, then another patch for the earth clamp. As the job got bigger, that earth clamp would keep creeping further and further away looking for clean steel.
Then I bought my first pilot arc plasma cutter and told him to borrow it for the weekend. When he brought it back, the first thing he said was, "Pete, there's no bloody comparison."
The big difference wasn't that the scratch-start machine couldn't cut the rusty panel once it got going. Once the arc was started and you kept moving, it would usually cut through the dirt, paint and rust well enough. The pain in the arse was getting it started in the first place.
If you're lying under a car or truck trying to cut something awkward, the last thing you want to do is keep crawling out to clean a shiny patch just so the bloody thing will fire.
That's the bit people miss. Sometimes the plasma cutter isn't faulty at all. You're just trying to get a scratch-start machine to do a pilot arc machine's job. If you want to know more about torch options, this article on swapping a handheld torch for a CNC torch also gets into pilot arc torches and what fits what.
One thing that's caught me out more than once is the earth clamp itself. Everyone checks the torch and the consumables, but hardly anyone checks the clamp. Have a look where the cable bolts onto the clamp. I've seen plenty where half the copper wire has burnt away over the years and it's hanging on by three or four strands.
It'll still sort of work, but it won't carry the current properly once you start asking a bit more of it. That's when the cut starts looking weak, messy or just all over the place.
While you're there, have a look at the copper braid that joins the two halves of the earth clamp together. Most of the better clamps have one, and after a few years of getting thrown around the workshop, slammed on steel and generally abused, they can crack or break.
The clamp still grips the steel, so you think it's fine, but electrically it's a different story. If that braid's broken, you're not getting a decent path back to the machine, and your cutting can turn to rubbish pretty quickly.
The next thing I'd check is your air supply. Not just whether you've got air, but whether you've actually got enough of it. I've seen plenty of blokes trying to run a plasma cutter on a little compressor that's flat out trying to keep up.
The regulator might say the pressure's right when you're not cutting, but as soon as you pull the trigger the pressure drops away and the plasma cutter starts cutting like rubbish. Then they start blaming the torch or the consumables when the compressor was the problem all along.
Power's another one that catches people out. A 45 or 50 amp plasma cutter isn't a little toy. It needs a decent power supply. Here in New Zealand I always tell people to run them on a proper 15 amp circuit if they can.
Another mistake I see is people plugging the compressor and the plasma cutter into the same circuit. Everything's sweet until the compressor kicks in halfway through a cut, then bang, out goes the breaker and everyone starts wondering what's wrong with the plasma cutter. There usually isn't anything wrong with it at all.
So before you start ordering parts or blaming the plasma cutter, spend ten minutes checking the simple stuff first. Have a look at what you're actually trying to cut. Move the earth clamp. Clean one small patch of steel. Try cutting a clean bit of scrap.
If you've got a scratch-start machine, remember its limits before you convince yourself it's broken. If the machine has suddenly gone weak, have a look at why your plasma cutter might have lost half its power. If it's just spraying sparks and not cutting at all, this article on plasma cutters that just spray sparks and won't cut is probably the next one to read.
And if the whole thing has just started cutting like rubbish out of nowhere, I've also covered that here: my plasma cutter started cutting like shit all of a sudden.
Before you blame the plasma cutter, check these first:
If you've checked all that and it's still cutting like rubbish, then it's time to start looking at the plasma cutter itself. But most of the time, the fault is sitting right there in front of you. Dirty steel, bad earth, not enough air, not enough power, or expecting the wrong type of machine to do the job.
