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Buying A Plasma Cutter

Q: What is Air Plasma?

A: Plasma arc cutting is a process where an open arc, much like in TIG welding, can be constricted by passing through a small nozzle, or orifice, from the electrode to the work-piece. The gas used, typically air, combines with an electrical current to create a high temperature plasma arc. When placed in contact with an electrically conductive material, the arc passes through the metal, melting a thin area. The force of the arc pushes the molten metal through the work-piece and severs the metal.

Q: What types of metal and applications can be used with a Plasma cutter?

A: Plasma will cut any metal that is electrically conductive including steel, aluminum, copper, and stainless steel. Keep in mind that your cut will be de-rated a little with the softer metals like aluminum, copper, and stainless. Rating refers to the thickness a plasma cutter can cut at a rate of 10 Inches Per Minute.

Q: Is there a lot of skill involved with Plasma cutting?

A: No. Depending on what you are cutting and a steady hand there is not a lot of training involved to operate a Plasma cutter. The torch should remain at a 90-degree angle and depending on the machine you can keep a standoff or drag either the tip or the drag shield on the metal.

As far as controls on the machine there are only two, which include the on/off switch and the amperage control. The on/off speaks for itself and the amperage is only going to change when you want to cut thicker material, but most operators will leave the amperage switch on full output for all thickness of metal.

Q: What are the necessary air requirements?

A: Compressed air is the most popular gas used for plasma cutting. You can use an air compressor or a bottle of compressed air. The CFM (Cubic Foot per Minute) is important because that is the amount of air that will be distributed per minute and will keep your Plasma machine running consistently. The PSI (Pounds per Square Inch) is the actual air pressure required to operate the machine. All machines need different PSI and CFM. For instance the Miller Spectrum 375 requires 4.5 CFM at 60 PSI to achieve a 3/8-inch rated cut, while the Spectrum 375 X-TREME requires 5 CFM at 90 PSI.

The other gas used is nitrogen, but the only advantages to using it are when cutting stainless steel. You will get a cleaner cut but the cut thickness will be diminished a little. With some exotic metals a gas mixture may be needed.

You will also want to have dry air when operating a plasma cutter. Miller offers a couple of Dryer/Filters that are designed to keep the air dry and clean. Dry air is important because if there is moisture in the line it will travel with the air and exit the end of the torch. This is not necessarily dangerous but will shorten the life of your consumables because the arc will follow the moisture in all directions and erode the tip prematurely.

Q: How big of a Plasma cutter do I need to buy?

Start by determining the type and thickness of metal you’ll be cutting and the desired cutting speed. Miller uses three standards: rated, quality and sever cuts. A rated cut is the thickness of mild metal that an operator can manually cut at a rate of 10 inches per minute (IPM). A quality cut is rated at a slower speed but on thicker metal. A sever cut is the maximum thickness a plasma cutter can handle. The travel speed is slower and the cut may require clean up.

Q: What kind of input power will I need?

A: Miller Spectrum plasma cutters have a range of power options.

The Spectrum 125C is available in 115V or 230V options. The Spectrum 375 and Spectrum 375 X-TREME can operate off 115V or 230V. The Spectrum 375 X-TREME can easily switch between the two, since the operator only has to choose the correct Multi-Voltage Plug for the receptacle.

Others can automatically adapt to a wide range of voltages, single or three-phase and compensate for power fluctuations in the supply. The Miller Spectrum 625 X-TREME and 875/875 Auto-Line are 208 or 230V machines with 40 amps of output. They have Line Voltage Compensation (LVC), which will give you a range from 176 to 264V. The machines will automatically handle any line fluctuations between those voltages.

These machines use Miller’s Auto-Line™ technology. Auto-Line allows direct connection to ANY primary power level: 50 or 60 Hz, single or three phase, 208 through 575 VAC. Simply connect the power cord to the correct plug or junction box and start cutting. Auto-Line lets you plasma cut at any location, on any job site and in any country without worrying about opening and manually linking the machine or damaging the machine from incorrect hookup.

This means you can plug this plasma cutter in anywhere in the world. Even with brownouts or other power fluctuations, as long as the voltage stays anywhere in that range, the cutting quality is unaffected.

These types of units are especially suited for working in the field, using an engine drive’s auxiliary power. In the field, units without this type of technology are prone to erratic cutting arcs, frequent breaker trips and blown circuit boards because they can place a load on the line such that voltage levels drop below the plasma cutter’s operating range.

Q: What about portability?

A: In addition to the ability to work with available power supplies, consider the plasma cutter's weight and size. All of Miller’s plasma cutters weigh less than 100 lbs. (The Spectrum 375 and Spectrum 125C weigh about 60 lbs.) Miller offers the No. 30A Economy Cart for these machines.

For the ultimate in portability, the Spectrum 375 X-TREME weighs only 18 lbs. and comes with its own shoulder strap to allow the operator to easily carry it.

Q: What safety procedures do I need to follow?

A: Proper welding clothing should be worn, as well as a number 5 or 6 shade full-face shield. Good ventilation is a must just as when you are welding. Be aware of potential hazards involved with the process including, high voltages, noise, temperatures, flammable materials, fumes, ultraviolet radiation and molten metal.