A plasma cutter cuts metal by sending air or an inert gas through a plasma torch, sparking an electrical arc, and then forcing plasma through the torch tip to cut metal. The arc of a plasma cutter can reach temperatures of 45,000 degrees F and provide one of the fastest ways to cut metal.
Plasma cutters have an on/off switch and an amperage setting that determines how much power to use for cutting. Provided the plasma cutter has enough power to cut through the metal workpiece, plasma is often a very safe, efficient, and clean way to cut metal.
While many mention the advantages of plasma over oxy-fuel cutting, a plasma cutter requires a significant up front investment. Though a plasma cutter will certainly pay off in the long run with its speed and low operating costs if you need to cut a lot of metal, it can be daunting to select the right plasma cutter for your business or home workshop needs.
The following guide will introduce some major factors to consider when purchasing a plasma cutter as well as some helpful links to the Baker's website where you can learn more about plasma cutters and related products.
Match Your Plasma Cutter to Your Work
As with purchasing a welder, the kind of plasma cutter you select will be determined by the kind of work you do. Unlike oxy-fuel cutting, a plasma cutter is capable of cutting just about every kind of metal. Therefore, the main consideration when choosing a plasma cutter is the thickness and amount of metal you plan on cutting. Below are some key questions to ask when trying to match a plasma cutter to your work:
- Are you cutting thick metal?
- How often will you use your plasma cutter?
- Do you need a portable unit?
- Are you willing to adapt your power outlets for your cutter?
- Do you have a generator you plan to use with your plasma cutter?
- Will your electrical current fluctuate?
As you review your plasma cutter options, these questions will narrow down your choices. While certain units will stand out for your particular needs, it's likely that choosing between brands will come down to what you're used to or what's recommended to you. The main difference between brands is that one manufacturer's standard feature may be an extra on another brand's machine.
There also are combination units that include a plasma cutter with a stick and TIG welder. If you just want a plasma cutter for the occasional job, this may be a great option provided you can find a unit that meets your TIG or stick welding needs.
Choosing a Plasma Cutter's Output Power
The output power of a plasma cutter will determine what it can cut. For example, 12 amps of output power from a 120V machine will be able to cut most 1/8 inch metal, while 60 amps of output power from a 230V machine will be able to cut most metals that are 7/8 of an inch thick.
There also are inverter-based plasma cutters available that provide high cutting output power, yet weigh much less than regular cutting machines that offer the same cutting capacity.
Choosing a Plasma Cutter's Cutting Speed
The cutting speed for plasma cutters is typically noted as Inches Per Minute (IPM). Your work flow and priorities will determine what you need, but keep in mind that while two plasma cutters may be able to cut through a 1/2 inch of metal, one may cut through the metal in a minute, while the other could take as long as four or five if it has a slow cutting speed. Choosing a machine with the right cutting speed can make the difference between a sound investment and a dip in your productivity.
Choosing a Plasma Cutter's Duty Cycle
The duty cycle of a plasma cutter is the amount of time it can operate continuously within a ten minute span before needing to cool off. A five minute duty cycle means a plasma cutter can run for five minutes before needing to cool off for five minutes. If a machine is run at a lower power, the duty cycle may be extended, though excessively hot operating conditions may shorten it. Using a machine beyond its duty cycle will cause it to overheat.
A longer duty cycle will be ideal for making long cuts or deep cuts on large pieces of metal, while a shorter duty cycle is ideal for a home shop where a series of small cuts are made regularly.
Choosing the Right Torch for a Plasma Cutter
There are two common types of plasma cutting torches. The most common torches are the high-frequency starting systems that create a spark with a high-voltage transformer, capacitors, and spark-gap assembly. High frequency torches have the advantage of not using any moving parts and therefore remain fairly dependable. However, they do require occasional maintenance and may create electric noise that can interfere with computers and other nearby electrical equipment in your office, shop, or home.
Another option is the contact start torch that uses a moving electrode or nozzle in order to produce a spark that lights the pilot arc. This kind of torch does not create inference with other electrical items and turns on instantly without a pre-flow cycle.
An excellent feature to explore in a torch is a drag shield that attaches to the cup of the torch and holds the tip at the ideal 1/16 to 1/8 of an inch from the metal being cut--this distance is known as the "stand off." The torch can be operated at full capacity with a constant standoff. The standoff distance is based on the thickness of the metal and the amount of amperage used to cut it, with low amperage cutting requiring little to no standoff distance.
If you plan on working on thin metal, you will most likely only need a single flow torch that works with limited amperage and does not require an extra flow of shielding gas in order to cool the torch. For larger cutting operations or users who plan on cutting thick metal, a dual flow torch with a shielding gas will make it possible to cut thicker metal at a high amperage.
Regardless of the way a torch ignites the plasma arc or utilizes a drag shield, choose a torch design that fits your hand well, especially if you plan on using it for extended periods of time.
Choosing Your Consumables for a Plasma Cutter
After making the initial purchase of a plasma cutter, the most important ongoing cost will be the cutting tips and electrodes. Therefore, before you pick up a plasma cutter, learn as much as you can about how fast your machine will use these items. A damaged tip from poor technique or a worn out electrode will either slow your cutting speed or reduce the quality of your cuts, and it's often recommended to change the tip and electrode together in order to achieve best cutting performance.
David Cook of The Fabricator suggests the following equation for determining the ongoing cost of plasma cutting units:
"Consumable cost, or the total consumable cost divided by the consumable life in hours of arc-on time per hour, is the most useful measurement. For example, if the cost of a nozzle is $4, the cost of the electrode is $6, and together a set lasts 2.5 arc hours, then the cost per hour, or CPH, is ($4 + $6)/2.5 = $4."
What Else to Consider for a Plasma Cutter
As with any large piece of machinery, it's important to test out a plasma cutter or to at least make sure the retailer offers a good return policy if the cutter does not live up to its promises. In addition, a reliable warranty will ensure your investment in a new cutting system will be a sound one for the long term.