Plasma Cutters For Low-Cost Plasma Systems

Now that you've decided to build or buy your plasma system, you need to purchase the plasma cutting unit. There are many that will work with these do-it-yourself systems and prices vary considerably. But which one is best for your needs?

Before you purchase a cutting unit, you should be cautious, because you might get a cutter that won't work properly with your plasma table's CNC controls.

Tom Caudle, owner of CandCNC, who is an electronics engineer and has been building controls since 2004 for plasma systems, mentions that you need three things from the plasma cutter to make it properly run with the CNC control.

The control needs to START the torch (turn on the torch typically using a relay). This is usually done through two wires from the cutter. Some plasma cutters are wired for remote START. In other cases, the two switch wires from the hand torch can be used. Then the control needs feedback to know if it's ON to allow the torch to move, which is a signal back from the plasma cutter to the control. It's sometimes called OK to Move or Arc Transfer or ARC OK. Finally for torch-height control, the CNC needs to see an ARC VOLTAGE measured between the workclamp and the electrode to the torch, (to control its height from the workpiece).

These voltages run back to the control through specific wires and a voltage divider card. Some torches have everything built in, such as the newer Hypertherm units. Others need to have a voltage-divider card added, or others have none of these and really can't be used for a CNC plasma system without some rewiring. So check the plasma cutter you purchase to see if it will automatically work with the controls you've chosen for your table system.

Caudle makes specific connection kits for Hypertherm units and some other brands and a universal connector and torch-height kit that works with just about any plasma cutter to provide the information that the CNC control needs to operate automatically. However, it only works with his controls.

ESAB

For low-cost plasma systems ESAB offer's its PowerCut series of plasma cutters.

Doug Smith, product manager at ESAB, says, "What we've done with the PowerCut 700, 900, 1300 and 1600 Series is virtually made them PlasmaCAM ready, where all the customer needs to do is to tap into the plasma cutter that has been pre-wired for the PlasmaCAM system.

"Besides PlasmaCAM, there are other competitors that use a different processing signal to start the torch. They use more of a CNC control output where they can divide the voltage down and tap into the start sequencing area of the torch, but it's a little more complicated. For our systems, we offer a separate package available for mechanized customers.

"Our PowerCut 700 is an entry level machine for customers such as those in the HVAC market or ones that are looking for a precision cut, but not doing high volume cutting. They would primarily want 100-percent duty cycle at 30A at 220V."

Using a drawn arc and an electronically controlled pilot arc, the PowerCut series offers starting reliability, cutting characteristics and consumable life without any electronic interference, mentions the company's website.

Other features that the PowerCut offers are: a digital readout display shows exact pressure or amperage, built-in line conditioner protects against damage from power-line noise and spikes, a tool-free quick disconnect torch and a rugged design that's lightweight for portability.

Hypertherm

When it comes to integrating with CNC tables, we have four plasma system options," says Erik Brine, product manager at Hypertherm. "It starts with our Powermax45 which is a 45 amp unit and goes up to our Powermax105, our newest system at 105 amps. Amperage level requirements are dictated by what is being cut, and how much you'll be cutting, which will drive the system you need to buy. We cover the full range of cutting characteristics, and have the greatest number of options available for our systems to match the proper system to the customer's needs."

Brine mentions that Hypertherm offers duty cycles "that would be very hard to hit with the type of usage these systems get. Hypertherm systems are designed so system overheating, even with heavy use, is not a problem.

"Also, all of our torches are easily interchanged. If you're working on a table and you want to do some hand cutting, within seconds you can change out the torch. You don't have to have the plasma system tied just to the cutting table."

Another important area of purchasing a plasma system is consumable life. If you're doing a lot of table cutting, consumable life is a very important consideration, more so than hand cutting, mentions Brine. "We typically outlast our competitors' consumables life by up to two to three times.

"Another important element is cut speed. When you're comparing systems of similar amperage levels, our cut speeds exceed the competition because of our consumable design. We use specially designed nozzles and shields that funnel gas flow to really constrict the arc. The more the arc is constricted, the hotter it is, and the faster it can cut."

Lincoln Electric

Lincoln Electric's Tomahawk 625 and 1000 Series can be used for hand or machine cutting. The Tomahawk 625 ($2,070) offers continuous output control that focuses the arc for different material thickness. A touch-start system reliably initiates a plasma arc without high frequency. A rapid arc re-strike allows fast cutting through gaps and expanded metal. A front-panel purge control makes it easy to set the air-flow rate without initiating the plasma arc. And a parts-in-place system detects correct installation of consumables and torch.

Lincoln Electric's Tomahawk 1000 Series ($3,087 and $3,298) offers all of the above along with a PowerConnect Technology that automatically senses and adjusts to input power for a range of 200 up to 600 volts, single or three phase, 50 or 60 hertz.

The 625 can cut 0.750-in. thick steel at 14 in. per minute and the 1000 can cut 1-in. thick steel.

Longevity

Imported from China, these three Longevity plasma cutters will work with plasma tables. Longevity's ForceCut 42i Plasma Cutter with Continuous Pilot Arc ($999.99) is capable of cutting up to 1-in. thick steel. According to the company's website, it weighs only 37 lbs. and uses 110/220V single-phase power making it very portable. It doesn't have an air compressor built in, but can use any shop or home compressor. It offers a five-year warranty for parts and labor.

Longevity's ForceCut 60i ($989.99) can cut up to 1.25-in. thick steel using 220V single-phase power while the ForceCut 80i ($1,209.99) can cut up to 1.75-in. thick steel using 220V single-phase power. All these plasma cutters can cut aluminum, stainless steel or even copper. All offer portability and a five-year warranty with a 30 day satisfaction guarantee.

Longevity's ForceCut 60i and 80i cutters use low-voltage starts. These offer 60-percent duty cycles.

Miller

Miller offers its Spectrum Line of plasma cutters that can cut from 0.125 in. steel thickness up to 0.875 in. Six units are available with duty cycles ranging from 12A at 35 percent at 120V for the Spectrum 125C (base price $1,200) to the Spectrum 875 Auto-line (base price $2,950) that offers 60A at 50-percent duty cycle using 230V single-phase power. All of the units can use single-phase power. But the Spectrum 875 Auto-Line can be powered by both single- and three-phase power.

Brian Brown, an electrical engineer with Miller, says, "We can connect any of our Spectrum plasma cutters to low-cost CNC tables. When it comes to connecting them, there are only a few wires that need to be connected to. There is very little work inside the plasma cutter that needs doing to set up a plasma system. Most of the low-cost table manufacturers provide a means to connect our plasma cutters to their tables."

Victor Thermal Dynamics

Thermal Dynamics offers its CUTMASTER A Series. These units offer a production cut quality on steel from 0.25-in. up to 0.625-in. thick.

At its website, the company mentions that the CUTMASTER A Series has been designed to offer a true production cut capacity as measured at a duty cycle of 80 percent (some other machines are rated at duty cycles of 40 or 60 percent, which may be less suited for automated applications). Understanding cut quality, cut speed and duty cycle eliminates having to buy a larger machine than is actually needed to get the correct capacity for an automated application.

"A lot of companies that purchase these plasma cutters only use them for an hour or two per day, maximum," says Dirk Ott, VP, global plasma automation brand. “Therefore, they're looking for a lower cost plasma cutter for a CNC plasma system. Our CUTMASTER A Series of air-cooled plasma cutters is a very good alternative to systems with water-cooled torches, which are more expensive. They are very flexible. You can cut all types of materials with them, whether it's stainless, aluminum or mild steel. More importantly, you can pierce material at the stated production cut thickness, which means you can start the arc in the middle of the plate. The alternative is an edge start, which increases consumables cost and cycle time.”

CUTMASTER A Series plasma cutters offer the ATC Quick Disconnect that makes it very simple to switch between a hand torch and a mechanized one. As a result, you can use the same system in the shop and in the field (even the largest of these units, the A120, only weighs 63 lbs.) With the ATC connection, the plasma system also recognizes when a mechanized torch is connected and will change the gas management protocols, so that they are best suited for automated cutting.

The CUTMASTER A Series offers a small interface on its back to connect to the CNC controls for start/stop and okay to move signals. These plasma cutters are delivered with a cable that plugs in to the back of the cutter and then the other side of the cable has four wires that can be easily connected to the CNC control.

CUTMASTER A Series ranges in price from $3,100 for the A40 to the CUTMASTER A120 at $5,400.