A question for the "experts" in here (i.e. professional CNC operators)... CNC vs NC

Someone in a local woodworking group was asking about CNC’s. Someone responded about Shapeoko, but felt the need to clarify that all the hobby CNC’s are not actually CNC’s, but rather “NC” (numerically controlled, but not “computer numerically controlled”). According to him and his instructor at a local technical training institute, the fact that they don’t have any kind of feedback was the differentiator.

This was the first time I’d ever seen the term “NC”, much less that all the hobby machines that are being sold are not actually CNC’s, no matter what the industry calls them. But admittedly, my training comes courtesy of Google and YouTube, so my expertise is rather limited. So I thought I’d post and see if there were any opinions in here.

I thought that one might also argue that since you can hook up limit switches to the MPCNC and LR machines, that could be considered feedback, as it helps the machine know where the tool is. But I’m more curious about the differentiation in general.


Just sounds like gatekeeping to me. Strap some servos on it and flip them the bird! Or don’t because that would be a waste of money. (Irt the servos, not the bird. You can still do that part)


I had some time on a friend’s CNC mill years ago and AFAIK it didn’t have any kind of feedback. I’d think the presence of feedback or not would be the difference between a closed loop and open loop system but they’d both be properly labeled CNC machines. After all, what’s spinning (controlling) the dials other than a computer? Sounds like a pair of 'C’s to me.


Im not a professional cnc operator but I do have a degree in computer engineering. To me the diffrence between a cnc and and NC would be a computer. I guess if you wanted to get technical most hobby machines wouldn’t be computer numerically controlled unless you hooked up and fed them from a computer or rpi (the mcu used as a brain in most hobby machines is technicaly not a computer). It would have nothing to do with feedback but rather the type of device controlling it. But that would be a very technical differentiation, with very little meaning. Like the diffrence between a digital clock and an analog clock, they function differently but either work in most applications. Most people would refer to either as simply a “clock” unless your an elitist in the field mad because your skills are being outdated by newer technology that you don’t want to take the time to learn.

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What would make it a computer? When I searched for a definition I got " A computer is an electronic device that manipulates information, or data. It has the ability to store, retrieve, and process data."

Doesn’t taking gcode(data) and processing it into a series of commands to control a machine fit the basics of that definition?

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Well, that’s basically my take on it as well. I did find this article on the history and evolution:

Every reference I saw to “NC” machines involved punch cards, and basically the controller read in the instructions and caused the movement to happen as it was read. But there was this quote:

So I can relate to the idea that our hobby machines are relatively “dumb”. You tell it to move 100mm, and it’s going to either move 100mm or something going to give as it attempts to follow your directions. But it also discusses things like CNC controllers handling things like acceleration calculations, which I believe is also included in the firmware of our Arduino systems.

The other side is this is that term definitions change. As @Atom said, at one point we differentiated between analogue and digital clocks. Heck the definition of “clock” would not likely have encompassed electronic devices kept accurate with atomic frequencies. So if everyone in an industry understands CNC to encompass both industrial class behemoths or desktop 3018’s, then the definition may have evolved. Or it may have been vague enough to not be specific about what level of “control” was required.

Anyway… It’s not a big deal. Was just annoyed by a know-it-all talking to down to everyone else more than anything. And was wondering if my understanding of CNC was incorrect.

Thanks for the input. Oh, and the guy spouting off was (I believe) younger than myself.


As a basic definition you are correct. But the technical definition is more subtle. Think of all the classic raspberry pies, they are all considered “computers on a chip” while the new Pico is considered an mcu. It comes down to the architecture of the chips used but basicly you can identify the diffrence because a computer runs an OS and a mcu runs a single program (even if it is a very large one like Marlin)

Think of the definition of life. If you google it it will say somthing like “somthing that grows, changes, takes in energy, excreetes waste and reproduces.” But a virus does almost none of those things (it only reproduces) but is still considered Alive. The general Google definition is not always the full technical definition.

I’m probably missing some subtlety here (I do have my talents :roll_eyes:} so a fuel injection control unit which takes numerous inputs(data) and calculates the correct injector open time (single program) is not considered a computer? Or has the working definition of ‘computer’ changed since rooms full of vacuum tubes labeled ‘computers’ have evolved into tiny chips whose architecture is a consideration?

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I’ve always thought this and similar definitions would make fire “alive” as well. :fire: :grin:

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This stuff strikes a cord with me. This isn’t a “computer numerically controlled” machine. It is a CNC machine. It has grown so much more than it’s original term. It no longer needs to be bound by the expansion of the acronym.

I hate seeing it defined in articles about it. It doesn’t clarify anything.

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Nope not considered a computer, probably not even a mcu. I’m not a car guy so I can’t be 100% sure but I would venture to guess that a fuel injector like you describe is plc. Plc is programmable logic controller they tend to run several orders of magnitude Afaster than a mcu and tend to be used in super fast applications (the video card in your computer is a plc to handle graphics at 60+ frames per second). If you take a really big plc and join it to a few mcu in the right way. Then you get the technical definition of a computer. Now the new modern cars that have a single integrated device that runs everything from the cruise controll to fule ingection to playing pandora from your phone is likely a computer on a chip, similar to an rpi.

Yup the diffrence is “organic compounds” that is what makes viruses living and fires not. A virus does not meet the general criteria but contains reaccuring organic compounds (spesificly a gene sequence) and fire meets pretty much all the criteria but contains no recurring organic compounds.

As for this I am not sure. My guess would be a mix of both the evolution of the word and just general use. I know the diffrence between these things, but I still tend to call them all computers in general company. Like you said before they all fit the general definition of a computer (witch is somthing that computes things, witch has a really interesting origin of being a person working for the weather service :crazy_face:). So I’m sure alot of things (like fuel injectors systems) being called a “computer” comes from the idea of if it has a bill and lays eggs, then it’s… a platypus… or a duck :wink:

In many respects I think our definition of ‘computer’ is an age thing. After all, when I was in school a Babbage engine was labeled a ‘computer’, no electronics at all. I guess I tend to think of a ‘computer’ as anything that takes input and uses it to ‘compute’ an output, many are very simple devices, like the simple circular slide rule pilots use that’s known as a flight computer that can be used to calculate things like wind triangles.

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Oh I understand, I too consider those things computers (and most fuction on a hardwired analog logic very similar to the digital logic processed by a plc) to me its not an age thing as much as a field thing. Not sure what you do for a living but I’m sure there are at least a few things in it that are defined differently then how the general public would define them. I was trained in computers so I know how and when the definitions break down. Maybe you know cars and could tell me the diffrence between a hot rod, a muscle car and a sports car (to me they are the same)

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I would still consider a PLC a computer. It is more similar to an arduino than anything. They aren’t that fast, they just only do one thing.

I had a class in college where we learned about arduino like processors, and it was called “micro computing”. We had to program in assembly first and it took most of the semester. That was honestly a waste of time.

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That all depends, it is basicly the digital equivalent to a relay system. A ROM chip could be considered a PLC. but so is every bit coin miner and video card. I say they are “faster” because they operate on a series of switches so an asynchronous plc program works at the speed of the propagation delay of the transistors inside the ic. In the order of picoseconds, much faster than any mcu. All “computer on a chip” systems are built on plc chips. I built (a crappy) one in collage on a spartan 6 fpga witch is a type of plc (the same series used in Allen Bradley plcs) so yes I agree that a powerful (witch are not hard to come by themselves days) plc could be used as a computer.

Those ‘definitions’ would likely be much looser than what defines ‘computer’ to most people. To me at least, old school hot rods are production vehicles that have performance enhancing modifications, often by the owner. Of course some build their own from scratch and the term still fits. Muscle car was a term likely started at the time Pontiac stuffed a big engine in a mid-size car and called it a GTO and in my eyes came to mean smaller cars with larger engines. Again, it’s a personal thing but I take ‘sports car’ to mean a 2 seat open car that’s fun to drive for driving’s sake, no destination required.

And FWIW, I’m retired but have done various things in the automotive world including time with 2 manufacturers, retail motorcycle shop, automotive machine shop, etc. Years ago a friend let me make some small motorcycle parts on his CNC mill, they were the bread crumbs that led me down the rabbit hole. :crazy_face:

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Maybe but maybe not… you said you call a slide rule a flight computer, And baggage machines. Do you think most people would consider those computers? It was actually the man who invented the first weather prediction service that created the term “computer”. He said if he could get a person to compute the atmospheric data for a small reagon then he could predict the wearher there. And with enough of those computers he could predict the weather around the world. If the original computer was a human the. Where is the real boundary? Of course the big brains need to draw lines in the sand somewhere and expensive classes will teach you where those lines are currently drawn but really it is more important where you draw the line :slight_smile:

I’m guessing you meant Babbage machines? And yes, I’d call them computers because you input your variables and they quickly calculate the results you’re interested in. But most people? I wouldn’t hazard a guess knowing that opinions run the gamut from ‘the computer said it so it must be true’ to ‘computer?, that’s the devil’s instrument!’.

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