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How Much Air Does a Plasma Cutter Need?

November 16, 2018

How Much Air Does a Plasma Cutter Need?

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Plasma cutters are great tools to have in the shop. You could hardly find a faster tool for cutting out all kinds of shapes out of metal plates and sheets. Before you get one, though, you should make sure that your shop can support it. One of the things that plasma cutters need is compressed air.

So how much air does a plasma cutter need? Air requirements vary by the unit, but generally speaking, a plasma cutter will require about 4-8 SCFM delivered at 90-120 PSI. This will cover units that are intended for up to 3/8″ thick steel to large units that can handle 7/8″ this steel.

Of course, there are caveats to this. Also, there are some things to keep in mind when matching a plasma cutter to an air compressor. Let’s go over some of these things that are worth knowing.

Examples of Plasma Cutters Along with Air Requirements

To give one blanket statement about air requirements for all types of plasma cutters offers no guarantees of success. Let’s go over some examples of common plasma cutters and what their requirements are. Then you can match this to what you have or are interested in.

Smaller units (3/8″ steel cutting) commonly have air requirements at about 4-5 SCFM at 90-120 PSI. Examples of this are the Hypertherm Powermax 30XP and the Miller Spectrum 375.

Medium-sized units (5/8″-3/4″ steel cutting) like the Miller Spectrum 625 and the Hypertherm Powermax 65 take about 6 SCFM at 90-120 PSI.

Heavy-duty units (3/4″-1″ steel cutting)like the Hypertherm Powermax 85 or the Miller Spectrum 875 will need about 7-8 SCFM at 90-120 PSI.

Really heavy-duty units (1-3/4″ steel cutting) like the Hypertherm Powermax 125 take about 9 SCFM at 85 PSI.

How to Match an Air Compressor to a Plasma Cutter

Don’t pair a plasma cutter that requires 4 CFM to a compressor that produces 4 SCFM. It’s unlikely that the compressor will be able to keep up. There are a few reasons for this.

One is that this is the max rating for the compressor. It’s like saying your car has a max speed of 160 MPH and then expecting it to maintain that speed on a long road trip across the country. It’s just not a good idea; you’ll burn out your compressor for sure. Good compressors ain’t cheap, either.

Another problem is that the output rating is calibrated to a particular altitude, temperature and humidity level. You’ll notice that there’s an S in front of the CFM rating. This means Standard Cubic Feet per Minute. This is calibrated to 68ºF, 0% humidity and at sea level. If any of these numbers rise, your compressor output will drop.

Here’s an example: If you live in Denver, Colorado, you’ll likely have a 20% efficiency drop because of the altitude. For those that live in Miami, Florida, you’ll probably have a 7% drop because of the humidity. If your compressor is sucking hot air in from a small enclosed boiler room, you might lose 10-20% efficiency.

If you don’t want to figure out compressor specs based on environmental conditions, just add a 50% fudge factor. For example, if your plasma cutter needs 4 CFM at 100 PSI, you should at least have a compressor that’s rated for 6 CFM.

Does Air Quality Affect Plasma Cutting?

The air quality is actually really important for plasma cutting. If there is oil or water in the compressed air, the cut quality will go down, and you’ll be burning through your consumables very quickly. Here’s a list of the consumables for a plasma cutter, all of which will be negatively affected by poor quality air:

  • Nozzle
  • Shield
  • Retaining Cap
  • Electrode
  • Swirl Ring

Another factor to keep in mind for air quality is dust control. Excessive dust that gets into the system can damage your equipment, mess up your electrode, and make your cuts ugly.

The solution for all of this is to buy an inline compressed air filter. It will take care of dust, oils, and moisture. These things are pretty hard to justify not getting. While you could drop a few hundred on an industrial version, you can get one that will work perfectly for your garage for well under $50. This will keep all of your tools in great condition.

The bottom line is that if your air isn’t filtered and dry, your cut quality will go down and your equipment won’t last.

Alternative Plasma Table Gases

While compressed air is the most common and cheapest for plasma cutting, it’s not the only option. You can also use other gases. Here are some other options, along with why you might want to use them:

Oxygen

This is an industry standard for cutting mild steel. It allows for really efficient cutting and the cut quality is excellent. The reason for this is that the oxygen reacts with the plasma in a way that keeps the spray fast and narrow, so the cutting is highly concentrated.

However, cutting aluminum or stainless with plasma isn’t recommended. Oxygen in the plasma will also put a lot of extra wear an tear on the consumables, especially during piercing. To counteract this, some advanced systems use two different gases; nitrogen for piercing and then oxygen for cutting.

Ultimately, though, oxygen is expensive. You’ll need a really efficient, streamlined system to take advantage of the faster cutting speeds in a way that makes cents. Awful pun intended.

Nitrogen

This is the best gas to use if you cut a lot of aluminum or stainless. Cut quality and consumables life is good (1000 starts is pretty average). For thick materials over 1/2″ though, it just doesn’t perform as well as other gases.

Ultimately, though, nitrogen systems often don’t make a lot of sense. Cut speed and quality are only a little better than compressed air, and nitrogen is significantly more expensive.

Argon-Hydrogen

This is awesome for thick aluminum and stainless. It’s the hottest burning gas in the typical lineup so it really boosts the heavy-duty applications. The only problem is that this stuff is really pricey, so you’re best off only using it when you need to.

The main challenge with these alternate gases is that your machine needs to be compatible. This is why lots of job shops and garages just go with a regular compressed air unit. It’s the simplest and cheapest to maintain. Usually, the only time that using other gases makes sense is when you’re doing a lot of well-paid production cutting.

Setting Plasma Cutter Air Pressure

A common oversight when using a plasma cutter is for operators to incorrectly set the air pressure. Many machines say that they work with a range of 90-120 PSI, so some people just set them to 90 and forget about it.

The recommended air pressure actually varies by material type, material thickness, and type of operation. For example, gouging usually takes higher air pressure than cutting.

Your best bet is to just thoroughly read your machine manual. Every machine is a little different, but your manual will likely give you a chart or two of recommended settings based on what you’re doing. You may decide to fine-tune these later, but they generally work really well.

At the end of the day, you need to make sure that your air supply meets the needs of your plasma cutter. With a compressor that’s too small, you could starve the plasma or burn out your compressor. If the air quality is poor, containing moisture, oil, or dust, you could damage your equipment and you’ll have lower quality cuts. If your air pressure isn’t set right, you’ll lose efficiency and your cuts won’t be as pretty as they could be.

How much air do you use on your plasma table? Leave us a comment below on what you have found to be beneficial on your plasma table.

Jonathan Maes

Hi, my name is Jonathan and I've been working in shops for 12 years. I thoroughly enjoy all the metalworking trades - I've worked as a manufacturing engineer, a machinist, a CNC programmer, a foreman and a toolmaker. There are few things I love more than a great project to sink my teeth into!

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