If you've built a custom classic truck, chances are you've had to deal with cutting metal-it may have been removing or modifying something old or installing something new. And, if you're like most hobbyists, you've tried a variety of tools to do the job including hacksaws, cutting torches, and abrasive wheels. But if you haven't used a plasma cutter you're missing the best tool yet and one that should be in your home shop.
What is plasma?
A common question is: "What is plasma?" The scientific answer is that it's the fourth state of matter: there's liquid, solid, gas, and plasma. OK, but what is plasma? Basically it is a gas that has been heated to such a high temperature that it is no longer a gas, and it becomes plasma.
Plasma cutting as actually an offshoot of the plasma welding process that was used during WWII to cut down production time in some applications. Similar in some respects to the TIG process, with plasma welding the arc is intensified by the injection of a gas into the electric arc stream. So much heat is generated that the plasma stream cuts, or "keyholes," the metal making a small hole as the torch is moved down the weld seam. During this cutting action the melted metal in front of the arc flows around the arc stream and is drawn together behind the hole (making something that looks like a keyhole, hence the name) as the metal cools it creates a solid bead. This process will weld material 1/2-inch thick or more without filler rod.
Like the welding process, plasma cutters use pressurized gas (such as compressed air) and electricity from an electrode to create a plasma stream that's approximately 30,000-degrees F moving at 20,000 feet per second. That's hot enough to melt the metal being cut while the pressure is great enough to blow the molten material through the cut rather than let it reform. The process can be up to 10 times faster than a conventional oxyacetylene cutting torch, and a cleaner cut is easier to achieve.
Plasma Cutting Tips
Use a straight edge, piece of flat stock, or virtually anything with a nice straight edge clamped to the metal to make a straight cut. If you are trying to build something out of 16-gauge or thinner, and it has to fit in a given space, make it out of cardboard first, and use the cardboard pieces for a cutting template. The plasma cutter can move so quickly the cardboard does not burn.
Remove the cover of the machine and blow the dust and dirt out of the unit every six months or a year based on usage. Make sure the unit has been disconnected from the power supply.
Check the cutting tip and electrode for wear frequently. If they are used beyond their service life, cut quality will be diminished, cut speeds will decrease, and you can damage the torch head.
Plasma Cutter FAQs
Q. If I need to cut a piece of 1/2-inch steel, can I cut one side, then flip it over and cut the other side?
A. No, for the plasma process to work properly without damaging the cutting torch, the air, and the metal removed, must pass completely through the metal being cut. If you were to cut 1/4-inch on the first pass, all the molten metal would be blown back up into the torch head, causing damage.
Q. If I turn the air pressure up, will the machine cut thicker?
A. No, you should only set the air pressure to the manufacturer's recommended setting.
Q. How far off the work should I hold the torch?
A. It all depends on the plasma cutter. Many machines have a "drag tip" design where you can actually rest the cutting tip on the work. Consult your owner's manual for the correct distance.
Q. How dry does the air have to be?
A. Most plasma cutters have a water separator/regulator, which is used to adjust the incoming air pressure. Generally speaking, the water separator supplied with most plasma cutters will filter out most of the moisture. However, if you see a lot of moisture building up in the water trap, then you should consider an additional drier for your system.
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