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How to choose a CNC plasma cutter

March 11, 2013

What you need to know to start looking for a CNC plasma

Well I’m not going to tell you who’s machine to buy. My answer to that might seem obvious. But I do want to discuss some of the questions and considerations that you should find the answers to before you even start looking for a machine. Having this figured out ahead of time will help you get the right machine for your shop, regardless of which manufacturer you wind up talking to.

Step 1: Sheet size

Start with figuring out what you need to cut. The most important question is the maximum plate size – do you cut 4’ x 8’ sheets, 8’ x 10’, 10’ x 40’? Plate size is where we start when deciding which model machine you will need. Every machine model is designed to cover a range of different plate sizes, but once you go beyond a certain point, you automatically get bumped up to a larger machine model. That’s just the reality of the machine structure and the ‘beam’ size. Nobody wants a 4 x 8 machine with a beam design that’s big enough to go 30’ wide – it wouldn’t be economical.

Maximum plate thickness is also used to determine which machine model you’ll need, because some models are limited by the size of plasma they can carry, or the maximum thickness they can clear.

The next part of the equation is how many sheets you need to cover. Most cutting machines are sized to cover a single plate width. But some high-production shops or steel service centers may want a machine wide enough to cut 2 plates side-by-side. That will quickly bump you up into a larger model gantry. Likewise, most machines can have rails long enough to cover one or more plates end-to-end. But the machine width is the more important question to answer – here’s why: you can almost always add more rail, but you can’t make the machine wider once it’s built.

Step 2: Working Areas

Another factor that affects machine size is the arrangement of working areas. The simplest machine only has one working area, which means the cutting table is big enough for one plate at a time. But that means that once you finish cutting the plate, the machine sits idle while you unload the cut parts and scrap, and then load a fresh plate. That’s fine for small shops or low-production environments. But many companies want to increase the machine’s efficiency by being able to load & unload while the machine is cutting. Here’s the trick though: do you get one big table, or two separate cutting tables? Whether it’s a water table or downdraft table, you could go either way.

Sometimes having an open zone between tables is nice for service access. Extra space between cutting zones also helps avoid smacking the machine with a plate swinging from a crane while trying to load the table. So the distance between one plate and the next needs to be at least the parking distance of the machine, plus a little extra. The more space you leave, the safer you’ll be. The problem is that every foot of additional rail length equals some additional cost and floor space used, so it’s always a trade-off.

Step 3: Process Tools

Having a good idea of what type of cutting process tools you need will also help narrow down which machine model you’ll need. Do you only need 1 plasma station, or 2? Do you need an oxy-fuel torch, or maybe 4, or 8 of them? The more tools you need, the wider the machine gets. And that’s not only because of the space each tool takes up on the gantry, but also because of the ‘cross-cut’ requirement.

Let’s think about a machine with 1 plasma torch and 4 oxy-fuel torches, where you need to cut 10’ wide plate. You are going to need that plasma torch to be able to cross-cut the entire 10’ wide plate. And you’ll probably want at least 1 of the 4 oxy-fuel torches to be able to cross-cut the entire plate as well. That means you’ll need room on the gantry for all 4 oxy-fuel torches to park off to the side while that plasma torch covers the plate. Likewise, you’ll need room on the other side of the gantry for the plasma station to park while one of the oxy-fuel stations covers the plate. As you can see, if you start adding more tools, like a 2nd plasma, a marker tool, more oxy-fuel torches, etc, the machine can get really big in a hurry. And a beveling station makes it even worse, because most bevel stations take up 24 – 36 inches of cross cut on the machine!

Step 4: Don't Forget About Software

Don't under estimate the importance of programming and nesting software. Even for a small shop where you won't need nesting capabilities, you still have to be able to generate program code for the CNC to run. Many new CNCs today have built-in programming capability, such as shape libraries or manual program editors. A lot of them also have the ability to take in a DXF file or DWG file and "post-process" it into M- and G-Code for the CNC to run. But even then you have to know how you are going to create and edit those CAD files for the CNC to import. There are lots of possibilities, but the point is that the machine is worthless if you can't generate programs to run it. So don't forget about the software when planning the purchase of a CNC plasma.

Step 5: Options

There’s a million of them. You are going to have optional features on the CNC, the plasma system, the oxy-fuel stations, the gantry, the software, the table, dust collectors, and on-and-on. The best thing to do is educate yourself on some of them ahead of time, so you can be sure to get the ones you need to make your business as profitable as possible. That might mean getting the high-end options to improve your productivity, or it might mean knowing that your business can get away without all the bells & whistles so you can keep the investment cost low. Either way, knowing what is available and knowing the cost & benefit of each option will help you make a better buying decision.

 

Posted in Cutting Systems , Tagged with CNC, Plasma

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