Most people blame the plasma cutter when their cuts look like rubbish.
Cheap machine.
Bad brand.
Dodgy Chinese junk.
Nine times out of ten, it’s none of that.
It’s air.
Bad pressure.
Not enough flow. Wet air.
I learned that the hard way in my own shed.
Quick Rant (Because It Needs Saying)
I see it all the time.
Blokes jump online and start shopping for another plasma cutter because their current one “won’t cut right”.
So they drop another $800… Hook it up to the same crap air setup…
And guess what?
Cuts still look like shit.
Then they reckon plasma cutters are useless.
No.
Bad air is useless.
You can bolt a $3,000 plasma cutter onto rubbish air and it’ll still cut like rubbish.
Air comes first.
Everything else comes after.
How I Learned the Hard Way
When I bought my first plasma cutter, I didn’t even realise I needed an air compressor.
Sounds stupid now.
But at the time I honestly thought the machine just made its own air.
So I dragged the plasma cutter home, looked around the shed, and thought:
“Well… I’ve got a compressor.”
It was a little 1hp unit with a small tank.
Used it for pumping tyres, blowing dust off benches, that sort of thing.
So I hooked it up and started cutting.
On 3mm steel?
Yeah… kind of worked.
Cut a small bracket.
Stop.
Wait.
Cut another bit.
But the second I tried to run a longer cut, everything went to shit.
Arc went weird.
Cut got ugly.
Machine sounded unhappy.
At the time I thought:
“Bloody cheap plasma cutter.”
Turns out…
The plasma cutter was fine.
My air setup was rubbish.
Same story whether you’re in Auckland, Hamilton, Tauranga, Wellington, Christchurch, or Invercargill.
Plasma cutters don’t just need air.
They need a lot of air.
And they need it consistently.
Air Does More Than Blow Molten Metal Away
Most people think air just pushes molten metal out of the cut.
That’s only part of the job.
Air also:
● Shapes the plasma arc
● Cools the torch
● Stabilises the cut
● Protects consumables
Bad air doesn’t just give ugly cuts.
Bad air burns tips.
You can have the best plasma cutter in the world.
If your air is crap, your cuts will be crap.
Simple.
Pressure vs Flow (Big Difference)
Pressure is only half the story.
Flow matters just as much.
You can have 100 PSI sitting in the tank.
But if the compressor can’t supply enough flow, pressure collapses the moment you pull the trigger.
Gauge says 100 PSI.
Pull trigger.
Pressure drops.
Arc weakens.
Cut turns ugly.
That’s not a plasma problem.
That’s an air supply problem.
Thicker Steel = More Air
Faster Cutting = More Air
No magic.
Thicker steel means more molten metal to blow out.
Faster cutting means more molten metal per second.
Both require more air.
If you’re trying to cut thick plate with a marginal air setup, you’re fighting physics.
You’ll lose.
My Compressor Upgrade Reality
After fighting the small compressor, I upgraded to a 3hp compressor with a 100 litre tank.
Huge improvement.
I was cutting 4mm plate in long lengths.
Still… it would eventually fall behind on long runs.
So I added a second air tank in-line.
Now I had:
3hp compressor
100L main tank
Extra tank in-line
With that setup:
I could cut a full sheet.
While I slid the next sheet into place, air rebuilt. Then I could cut again.
Doesn’t matter if you’re in Whangārei building trailers, Rotorua fixing farm gear, or Timaru cutting brackets.
Plasma cutting chews air.
Rough Pressure Range (Don’t Obsess)
Most small to medium plasma cutters like somewhere around:
80–110 PSI (5.5–7.5 bar) at the machine
That’s a starting point.
Not a magic number.
What matters more than the exact number is:
Does pressure stay steady while cutting?
If yes → you’re good.
If it nosedives → you’re not.
The Gauge Lies (Unless You Watch It Cutting)
Setting pressure with the trigger not pulled means nothing.
Set pressure.
Pull trigger.
Watch gauge while cutting.
That number is what matters.
Tank Size Matters More Than People Think
Big tank = buffer.
Small tank = instant pressure drop. For plasma cutting, I’d rather have:
Moderate motor Big tank Than:
Tiny tank
Screaming motor
Dry Air = Happy Consumables
Moisture kills tips.
Water in the airline causes:
● Arc instability
● Pitting inside the tip
● Short consumable life Bare minimum:
One moisture trap at the tank.
Better:
One at the tank.
One near the plasma cutter.
Cheap insurance.
Hose Size and Length Matter
Long skinny hoses restrict flow.
Restriction = pressure drop.
Use decent diameter hose.
Keep it as short as practical.
Same idea as using a thick extension lead for power.
Regulator Location
Set pressure at the machine.
Not at the compressor.
Hoses, fittings, and filters all cause drop.
You care about what the plasma cutter actually sees.
Plasma Cutter Settings Are Simple
You’ve got two main knobs:
● Amps
● Air
That’s it.
Set amps to suit thickness.
Set air so pressure stays stable while cutting.
Done.
Simple Dial-In Method
Start around 90 PSI.
Make a cut.
Listen.
Watch.
If arc sounds rough → add a bit of air.
If cut looks blown out → back air off slightly.
Your eyes and ears beat charts.
Every time
Good Starter Compressor (Home Shed Use)
If you’re mostly cutting brackets, tabs, and short runs:
A 3hp compressor with a 100–150 litre tank is a solid starting point.
Not perfect.
But workable.
If you’re trying to run long production cuts?
You’ll want more tank and more flow.
Biggest Takeaway
The plasma cutter is usually not the problem.
The air setup is.
Once I sorted my air properly:
Cuts got cleaner.
Arc got smoother.
Consumables lasted longer.
Same machine.
Better air.
Final Answer (Straight Up)
Why do your plasma cutter cuts look like shit?
Because your air pressure and flow aren’t stable.
Run roughly 80–110 PSI at the machine.
Use dry air.
Have enough compressor and tank behind it.
Then set amps to suit thickness and cut.
Stop chasing perfect numbers.
Chase stable cutting.
That’s what actually matters.