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Low-Cost CNC Plasma Systems, Part 1 of 4

October 2012

Can a CNC-plasma system that’s less than $10,000 work for your shop?

If you’ve always had your eye on a plasma system, but couldn’t afford one, today you probably can, as there are now many options for owning one.

But are these low-cost systems the right choice for your shop?

This article is the first in a series. In this article, we’ll explore what these systems are all about and their limitations. Future articles will review what’s needed to build one, such as the controls, software, support and where to find free plans for a system. We’ll also look at available kits, partial and finished plasma systems and what plasma cutters can be used to complete a system.

Jim Colt, applications technology manager at Hypertherm, has two low-cost, plasma systems that he uses to gain experience with to help shops that want to purchase one, and to find out how his company can support them and make them better.

FSMD: What do you think of these low-cost plasma systems?

Colt: I think a lot of the people that are looking at these entry-level plasma systems need something, but they really can’t afford or don’t want to spend the money for the higher-end plasma systems. In fact, this market segment has been a hugely growing one within the last 10 to 15 years led by the likes of Torchmate and PlasmaCam and a few other manufacturers.

The real attractive thing for these systems is that small shops can purchase one with a low capital-equipment cost compared to the $100,000 machines. Now they can get a plasma system with a 4 ft. by 4 ft. table and torch-height control easily within the $10,000 range.

There are a few manufacturers of complete, entry-level CNC-plasma cutting machines that start at prices below $10k. None of the plasma cutter manufacturers (like Hypertherm) produce the complete cutting table, and none of the cutting table manufacturers produce the plasma cutter. It’s the buyer’s choice to either buy the cutting table and the plasma separately and interface them together, or purchase the cutting table and the plasma cutter directly from the cutting table manufacturer.

FSMD: How good is a plasma system that’s less than $10,000? Can a shop really do things with it, or are they wasting their money.

Colt: Air-plasma systems used with these low-cost systems have been dramatically improved by all the manufacturers for consumable life, cut quality and things like this. They are now a pretty reliable option for CNC-plasma cutting.

Cut quality using regular compressed air with a plasma system on a CNC machine from an appearance point of view looks almost as good as what’s available from a high-definition plasma system that could cost $100,000. However, there are some cut edge metallurgical and appearance differences along with productivity on how fast you can cut with them. There are differences in consumable life that boils down to cost per foot cut too. These consumables include the shield, nozzle and electrode as the most commonly replaced parts in the torch.

We’ve found that the air-plasma systems’ consumables used on these entry-level machines don’t last as long as typical industrial, liquid-cooled-plasma consumables. Therefore, more consumables will be purchased. In reality it costs a little bit more to cut parts with them.

FSMD: How are these CNC-plasma systems designed?

Colt: The vast majority of entry-level, plasma-cutting machines use a standard PC or laptop-style computer as the CNC control, and use an off-the-shelf software like Mach3 as the motion-control software. This software accepts a CAD drawing and converts it into electrical signals (through a breakout-motion-control board) that drive the X, Y and Z-axis drive motors, and also operates output signals that start and stop the plasma system as well as any other tools (plate markers, etc.) that might be on the machine.

(Other pieces needed for a complete plasma system include the cutting table, a gantry that provides the axes motions linked to a CNC-motion system that includes the drives and motors to accurately move the torch and a plasma-torch holder.)

FSMD: Are there important features these plasma systems need to be productive?

Colt: The best systems, and you can barely fit these into the under $10k price range, also have full featured, torch-height control that automatically controls the plasma-torch pierce-and-cut height.

You need a torch-height control because sheet metal usually isn’t flat, and height control manages the distance from the torch tip to the metal it’s cutting. Also when a torch starts cutting, the thermal stress it introduces into the metal will start warping it. So it’s no longer flat. Without the torch-height control capability, the operator will be standing next to the machine babysitting it while it’s cutting.

Without it, you can also expect lower consumable life, reduced cut quality and cut part accuracy and much lower productivity. Torch-height control is necessary for the best performance on any computer-controlled, plasma-cutting machine.

Torch-height control also effects cut quality along with consumable life almost equally. Without it, you’ll probably need more secondary operations on a part’s edge, as height control directly affects cut edge angularity, cut quality and accuracy. You can’t buy an industrial machine without height control.

FSMD: What about plasma cutter consumables? Do they affect cut costs?

Colt: People who have plasma cutters look at the price of the consumables. For instance, how much is an electrode and how much is a nozzle, looking for the cheapest ones. Other people who have used plasma cutters realize that the cheapest electrode and nozzle are not necessarily the cheapest ones to use. If you look at a latest major-brand plasma system with the newest technology, you can buy a nozzle that costs $4 that might last for several thousand feet of cutting. Or you can buy an imported plasma system with a $1 nozzle that might last for several hundred feet of cutting. The cheapest one is the one that would give you the longest cutting capability. You must think about performance along with cost.

FSMD: With an inexpensive system, what’s the maximum metal thickness you can?

Colt: The CNC-plasma machine doesn’t make a difference. It depends on the plasma torch that’s purchased. What’s important though is how thick of a material can the plasma pierce. My Powermax85 can pierce up to 0.875-in. thick material. But if there are no internal holes cut out and you are just cutting from an external cut out, I can cut 1-in. thick material with a 45-amp plasma torch with an edge start. It’s the piercing capability that limits how thick you can cut. Look at this capability, and what your needs are before you purchase the plasma cutter.

FSMD: Are there any other aspects of these systems to be aware of?

Colt: As mentioned, these low-cost plasma machines are primarily operated using a standard office PC or laptop as the CNC control. Therefore, they can’t be used with on industrial-plasma gun, because industrial-plasma guns use a high-frequency starting technology to fire the torch. For Hypertherm’s high-definition plasma, we use a high-voltage, high-frequency discharge to fire the torch. If it’s used with a non-industrial hardened PC, it could burn up components in the electronics and electrical drives.

Most of these entry-level machines have to be used with non-high-frequency-start plasma systems, typically reserved for the low-end air-plasma systems. If you’re looking at a Hypertherm plasma cutting unit for a system, it would be all of our Powermax Plasma Systems that use a blowback starting system and not a high-frequency starter.

FSMD: How would someone get started in building their own system?

Colt: There is a large contingent of “do-it-yourself” machine builders that usually buy components from a company called CandCNC (www.candcnc.com). They produce very low-cost, pre-engineered and wired components including the drive electronics and motors, the torch-height control systems along with the CAD and motion-control software (Mach 3). A well equipped fabricating shop can build all of the metal parts of the CNC-plasma table often saving money in the process without having to reinvent all of the electronics and software. These machines can often be built for much less than $10k, including the plasma system.

The next article will cover how to build your own table and the components you’ll need.

CandCNC
Hypertherm