Maker 101: What is a CNC Machine?

We love our digital tools here and on this episode of Maker 101 we are going to talk about “CNC” machines, specifically what they are in the first place.

You may be familiar with the differences between a few types of CNC machines such as laser cutters, CNC routers, and 3D printers, but why are all of these classified under the same family of machines? They aren’t similar at all? Are they?

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Turns out they are! The common trait that groups them all together is that they have a computer controlling the motion of the machine; This informed the term CNC which stands for Computer Numerical Control.

So let’s answer the big question: what makes a CNC and how can you transfer your knowledge about one CNC device to another?

To really boil it down as the name suggests, all CNC machines need two things: Numerical control of its motion and a computer that drives it.

The Numerical Control Aspect simply means that rather than using your own eyes and markings on your material to make a cut, you can somehow tell the machine to make the cut for you to a certain dimension. By assigning this task to the machine, the result is usually a lot more precise than what we can manage with our eyes and hands.

By using a combination of motors with very fine precision, sensor feedback to measure the exact position, and a gantry with smooth motion, you can tell a CNC machine to move to a particular orientation within a millimeter of accuracy. Not only the final position, but you can numerically control the path the tool head follows to reach the final position. This means that with the help of a CNC machines you can achieve near perfect circles and arcs, straight lines and even complex shapes like text with minimal effort.

The Computer Aspect of CNC just means that this machine is programmable. You can use software to generate a set of steps for the machine to follow and the computer can replicate those steps with your material. The computer is also responsible for handling the sensor feedback and telling the motors how much to turn and at what speed.

The computer is the brains of the CNC operation. The motors are like your hands, which actually execute the tool actions. The machine’s many sensors are like your eyes, which tell you where to cut and when to stop cutting.

What makes CNC machines all appear so “different” at first glance is that the actual thing that is being moved around at the end of the CNC machine is different. They have a lot more in. common than they have differences but let’s take a minute to go over what those differences are.

A CNC Router is cutting into wood, or another material with a router bit. It creates shapes by subtracting material. You need to set things like the hardness of your material, the speed of the spindle, and the speed of the gantry.

The head of a 3D Printer is kind of like a tiny glue gun that melts and then extrudes filament. 3D prints are created by building up material. A user needs to specify how hot the nozzle should get, the speed of the gantry, and some other parameters regarding how the filament is deposited.

A Laser Cutter moves around the end of a laser and heats material to either engraver it, or cut all the way through. On a laser cutter the power of the laser needs to be set, the speed that it moves, as well as to what height you wish it to be focused to.

Now let’s talk about workflow. The workflow for all CNC equipment is pretty standard: You need to generate the files needed for your CNC computer to command the motors, You need to set a starting point for your CNC to reference all its motion on, and you need to make sure the CNC’s tools are set up correctly within the machine.

Generating the files can vary quite a bit in difficulty; it’s an entire skillset in its own rite.  Sometimes all you need to do is find a file on the internet and the machine can use it…. More often than not it isn’t that simple.

With CNC routers for example, you may need to generate what is called ‘gcode,’ which is a kind of machine language telling the CNC how to move. This can get very complex depending on how many parameters of the machine you want to control. Another example I’ll give is to get a 3D print, you need to generate a 3D model of the file. Basic geometric shapes can be pretty easy to generate, but more complex parts take more skill to model. It’s kind of like drawing or sculpting… it takes practice.  There are some resources online where people share 3D models they’ve done, and other file types for different CNC machines; Ill link some in this video description. However, with it being open source, sometimes we have found fantastic high quality files, and other times they need tweaks.

Setting a starting point, also called a ‘machine home’, is important because if you don’t set this, the machine doesn’t know which direction is up, down, left or right. This is how you check that the part is within the bounds of the machine and set the scale of the part.

Since CNC is clearly much better than what humans can do, why don’t we always use CNCs? The main reason is that sometimes CNC is just overkill for the task. If you just need to shorten a 2×4, you could probably get the precision you need with a hand saw, rather than going through all the steps of generating gcode, setting a home and cutting the wood on a CNC router. Using a CNC is an expensive and time consuming solution to this simple problem. Similarly, there may be things a CNC simply cannot do. For instance, a laser cutter cannot control the height of a cut into a piece of wood, so it may be better to just use a chisel and some sandpaper.

When should you use a CNC? You should use a CNC when you need precice cuts that you could not do by hand, but are within the geometric limitations of the machine. You should use a CNC if you need highly replicable parts – multiple copies of the exact same thing. Consider using a CNC for complex geometries like arcs or curves completed in a timely manner.

So there you have it: CNC Machines. Despite the fact that our laser cutters, CNC Routers, 3D Printers, and Vinyl Cutter are all used to accomplish different task, they have a lot more in common than they are different. Hopefully you learned a little something that you didn’t know before and we will see you next time!

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