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How Can I Make Clean Plasma Cuts?

November 17, 2018

How Can I Make Clean Plasma Cuts?

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There are very few things quite as annoying as when you’re fighting with your tools. Generally speaking, a well-maintained plasma cutting system runs like a dream. Sometimes, though, you’ll be banging your head against the wall.

So how can you make clean plasma cuts? You can make clean plasma cuts by cutting at the correct speed, replacing worn consumables, ensuring that the work clamp has a good connection, using clean, dry air, and maintaining the correct standoff distance.

Let’s go over all of these steps, as well as a few others, to make sure that you’re getting the most out of your equipment.

Replacing Worn Consumables

This is a common culprit for ugly cuts. Plasma cutter parts aren’t designed to last forever, they wear out and need to be replaced. There are generally five things that you should count as a consumable on your machine:

  • The shield
  • The retaining cap
  • The nozzle
  • The electrode
  • The swirl ring

Here’s the rule of thumb for when to replace the nozzle: If the hole looks kind of oval-shaped or bigger than it’s supposed to be, change it. It’s good practice to replace the electrode and the nozzle at the same time.

Generally, a visual check will be enough to let you know what needs to be replaced. If you have an extra one of everything in your toolbox, then you’ll know what these things are supposed to look like. The other perk is that you won’t be waiting for replacement parts to be delivered when your setup isn’t working properly.

Checking the Work Clamp

Made sure that your clamp has really good contact with the workpiece. Otherwise, the connection could end up being intermittent and it’ll mess up your cut.

If there’s any rust, paint, mill scale, or another kind of coating on the metal, pull out a flap wheel grinder and clean the area you want to clamp to down to bare metal. This will help to ensure a nice, steady connection for the system to work smoothly.

Clean Air for Plasma Cutting

If your compressed air has moisture or oil, you’re going to have a really miserable time keeping your consumables in good condition and your cuts clean.

The easiest fix to this is to simply install an inline filter that will take care of the problem.

Standoff Distance

The arc should be kept between 1/16″ and 1/8″ above the workpiece. Electric arcs can be finicky, so if you don’t maintain this, you’ll probably have some major issues.

If you’re using a plasma table, you should have a function where the controller will take care of this automatically. Even still, if you’ve tried everything else and nothing is working, then maybe just double check to make sure that this is functioning as it should.

Use a Drag Shield for Handheld Units Over 40 Amps

Under 40 amps, this doesn’t really matter. But if you’re using a handheld machine over 40 amps, then a drag shield is a really good idea. It just removes one more thing that you’d need to concentrate on while cutting.

A drag shield is just a little tube type of thing that fits on the business end of your torch. If you let it slide against the workpiece, then it’ll maintain that really consistent distance between the torch and the work.

If you don’t have a drag shield and are totally opposed to spending a couple of bucks to pick one up, then you’ll just have to pay close attention to the torch movement. Most people find it easier to use both hands when cutting like this. One hand holds the torch and guides the movement, the other hand props up your cutting hand to keep the torch height steady.

Seriously, though, just get the drag shield.

CNC Plasma Machine Settings and Setup

The owner’s manual is a wonderful source of information on how to set up your equipment. I would know, I read one once.

Anyway, if you still can’t figure it out after thirty-something tries on your own, it might be time to swallow your pride and look around for that condescending little booklet. It should have a bit of information that describes what the machine is capable of, along with how to handle different materials and thicknesses.

One thing that you’ll want to make sure of is that you’re using the right tip for the amperage setting. You should have at least one tip for high amperage and one tip for low amperage. Running the wrong tip for the set amperage will lead to premature wear. That means that you’ll need to either fork up some cash or suffer the shame of shoddy workmanship.

Plasma Cutting Techniques

Sometimes you can’t blame your tools. The problem might be you. Here are some things to watch out for when you’re using your equipment.

Piercing

When piercing through the thicker material, start with the torch on a 45-degree angle. This will help to prevent backsplash when the molten material sprays back as the plasma is working through the material. If you keep the torch at a 90-degree angle for thick piercing, the backsplash will really wear out your consumables, which will, in turn, affect your cut quality.

For thinner material, though, this isn’t necessary. The plasma will punch through the metal quickly and efficiently.

Cutting Speed for Plasma Cutters

If you don’t cut fast enough, you’ll end up with an ugly cut. Some materials, like aluminum, are especially sensitive to speed.

How can you tell if you’re moving at the right speed for your plasma cutter?

To cut at the correct speed for a plasma cutter, watch the sparks. If the sparks are coming down straight under the workpiece, you’re cutting too slow. If the sparks are spraying above the workpiece, you’re cutting too quickly. Your sparks should come down at an angle of 20 degrees beneath the cut.

If you’re using a machine that can easily handle the thickness of metal that you’re working with, then you should be able to nearly totally eliminate the slag at the bottom of the cut by increasing your cutting speed. Ultimately, though, the more consistent your speed is, the nicer the cut will look.

Some guys find that, for handheld machines, it’s easier to keep the torch speed constant and steady when they’re pulling in instead of pushing the torch out. Either way, make sure you trace the motions before starting so you can get a feel for a good position.

If you’re cutting thick material, crank the power on your machine to the max and adjust your travel speed to maintain good cutting conditions. For thin material, keep the amperage low and swap out for a low-amperage tip. This will keep your kerf clean and tight.

If you’re using a hand-held unit to do something really precise or repetitive, consider using a guide. You can buy straight and circle guides that are very easy to use. For more complex shapes, you can make yourself a pattern. This will allow you to focus more on maintaining a good speed instead of on trying to make the right shape.

Conclusion

Plasma machines are actually very reliable and work great when they’re properly taken care of. If you’re just starting out, it can take a little bit of practice to get nice, clean cuts that don’t have globs of slag on one side.

Even if you’re not doing the best job of cutting, this slag generally isn’t very hard to tidy up. A wire wheel or a quick grind should blast it off no problem. But if you take a bit of time to practice with some test cuts, you should be able to get cuts that look nearly perfect.

Post a comment below and let us know what you do to improve your quality when plasma cutting.

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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