What You Must Know Before Buying a Plasma Cutting System

More and more shop owners are deciding that CNC plasma-cutting tables are great additions to their shops. The computer-controlled robotic arm can guide the plasma torch over the surface of the work to create intricate and complex cutting patterns.

With the ability to cut so precisely, the money-making possibilities are endless; create metal art for sale at trade shows and art galleries; create complex HVAC ductwork with ease; create a prototype of a concept part; create one-off or hard to find mechanical parts. But buying a CNC machine is not as easy as running down to the hardware store and picking one up. You’ll want to consider a few questions to help make your buying decision easier. With careful research beforehand you can save yourself and your company considerable time and expense.

MACHINE QUALITY
First and foremost, the number one thing to make sure of is that you’re getting a high quality machine. CNC plasma cutting tables (no matter the manufacturer) are expensive. Do your homework beforehand and make sure you’re getting the highest quality your budget will allow.

Materials
You’ll want to check on the quality of materials used in construction of the frame. Is it steel? Aluminum? Something else? Steel is stronger than aluminum, of course, so the steel machines will require less material and will be lighter, but will have the appearance of flimsiness. Aluminum machines will be bulkier, but will have the appearance of strength. Machines made of either material will have more than enough strength for even the biggest jobs.

Design
You’ll want to check on the quality of the table design. So many factors can affect the performance of the table, and the slightest variation in even the smallest factor can alter table performance. For example, if the gantry (the big heavy bar that slides up and down the length of the table) is too heavy, it makes the torch difficult to control with high speed and accuracy. A light-weight gantry, on the other hand, can produce amazingly accurate results at high speeds.

Also consider rolling surfaces. Sealed ways keep out more dust and grit, but they can’t keep out all of the inevitable plasma dust Eventually the dust will mix with the oil and create a gritty sludge that will chew up the parts. Because it’s sealed, you’ll have to replace the entire component. Unsealed parts, however, are much simpler. An unsealed roller on a simple way can be wiped completely clean in a second, and should a part need to be replaced, it can be accessed without replacing the entire component.

Motors
What sort of motors control the torch? Servo motors are widely recognized as superior to stepper motors. A servo motor can move to an infinite number of positions within its range of motion, and it provides feedback to the controller, telling the controller where it happens to be at the moment. A stepper motor has a finite number of positions it can move to and provides no feedback to the controller. Thus, it sometimes happens that the controller will tell the stepper motor to move a certain number of steps, but the controller has no way of knowing if the requested movement actually occurred.

If the torch hit a snag or otherwise didn’t move for some reason, the entire cut path will be offset from where the controller thinks it is. Of course, servo motors are more expensive than stepper motors. Just take care that your attempts at cost-cutting don’t hamper your ability to cut quality designs.

SOFTWARE
The software that runs the equipment and designs the drawings is arguably the most important component of your CNC plasma table setup. The software performs two distinct functions: designing the piece to be cut, and controlling the table and the plasma cutter. Although high-end design software like AutoCAD is perfect for creating high quality designs for a large number of applications, be careful you’re not using a sledgehammer to swat a fly.

AutoCAD and the like have built-in functions to handle extremely complex requirements, and often those extra functions can distract the user and actually inhibit the creation of perfect cut-paths. A better option is to look for software specifically designed for creating CNC plasma cutting drawings. This software is optimized for making perfect cut-paths, and can do so quickly and easily. Controlling the table and the plasma cutter must be performed by the software that came with your table. The best software will be created to maximize the characteristics of the table it’s running on.

Be sure to look for software created and optimized specifically for your table. Ideally, the software running the table should be written by the same company that makes the table. This will help you avoid the all too common response “that’s not our problem, call the software vendor” if you ever have to call for technical support.

DUST AND SMOKE
Plasma cutting produces a hefty amount of dust and smoke. Without proper ventilation or other dust-containment measures, the dust and smoke can quickly overtake an enclosed room. Most cutter manufacturers recommend their cutters not be used outdoors, which means you’ll have to provide your own indoor containment measures.

Downdraft
A downdraft system consists of skirts around the base of the table that enclose all the area under the table, and a fan that sucks air down through the table and outdoors (or through your air-filtration system, if you’re recirculating the air). This is a very simple and effective system for eliminating dust and smoke, but typically must be custom configured for each installation. When comparing tables, be sure to ask about a downdraft system. Does the machine come with downdraft components, and if so, are they stock components or can they be customized?

Water Table
A water table is another dust and smoke containment system, consisting of a shallow table of water placed under the cutting surface of the table. As the machine is cutting the metal, sparks and dust are blown down into the water where they are quickly doused. When using a water table, be extra careful to keep all electrical components away from the water. Also be sure to ask the table manufacturer if water tables are recommended with their cutting tables. Water can splash, and sometimes the underside of the cutting table can become rusty with excessive or incorrect use.

FINALLY . . .
Last but not least, be sure to check out the warranty that comes with the table. Does the company stand behind their products? A longer warranty period is better than a short warranty period. Does the warranty cover all parts, or just some of the parts? What happens if something goes wrong after the warranty expires? How much do replacement parts cost?

By the time you’ve compared all the options and answered all these questions (as well as other questions specific to your unique setup), you’ll be in a clear position to make a wise purchase. No longer having to take your cutting projects to the shop across town should save significant time and expense, and might even make you the go-to shop for others’ cutting projects.

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