What Is a Computer Numerical Control (CNC) Machine?

A X-Carve CNC machine with spinning carve bit.
Inventables

A Computer Numerical Control (CNC) machine is, as its name suggests, a computer-controlled machining device for creating things. Chances are, you own a product that was either made by or prototyped with a CNC machine. Here’s how they work.

What Is a CNC Machine, and How Does It Work?

If you own a car or tablet, have flown in a plane, or have any medical implants, CNC machining made all that technology (and much more!) possible and available to you. A CNC machine is, at a fundamental level, a cutting tool controlled by a computer. They vary in size, shape, and type of material they can cut.

To understand how a CNC machine works, imagine how a 3D printer works, then reverse the process. Instead of extruding layers of plastic to build up an object, a CNC machine moves a cutting tool to remove material from an existing object. Here’s a timelapse of a CNC cutting a guitar body out of a slab of wood:

It’s a bit like sculpting, but on a very tightly controlled level. You place your material (like wood, metal, or foam) into the machine, and then a cutting device carves away at it. And much like with a 3D printer, you create a 3D representation of what the final product should look like, along with adjusting several settings to help you get there (how much material to remove at once, etc.).

The benefits of a CNC machine are time and repeatability. CNC machines work quickly (compared to a human), and can make the same cut accurately multiple times. That level of accuracy and precision is essential when it comes to mass-producing a particular shape or item the same every time.

The downside is, just like with a 3D printer, if you don’t have your settings correct and your 3D file’s geometries accurate, things can go horribly wrong.

How exact a CNC machine works varies based on its cutting method.

The Three Common Types of CNC Machines

CNC machines vary in two significant ways: the tool used to cut the material, and whether that tool, material, or both move in the machine.

Drill CNCs Make Frequent Repeatable Holes

Drill CNCs are just what the name implies. The CNC machine uses a drill bit for its cutting tool, and typically it can move up, down, left, right, forward, and back.

This type of CNC is useful when you need to create many parts with a necessary hole (or holes), and you need to place that in the same spot every time. Often that’s for assembly reasons, such as the pieces to an engine block.

Lathe CNCs Spin the Material

A lathe CNC differs from most of the other CNC machines by moving the object you plan to shape. Just like in a standard lathe, the wood or metal you place into the machine spins at a rapid speed. A cutter then moves towards the object and shaves off layers.

Ultimately, the final product will be cylindrical or sphere-shaped. As such, lathe CNCs are often used to make baseball bats, pool cue sticks, musical instruments, table legs, and even bowls.

Mill CNCs Shave Off Layers

Mill CNCs (also sometimes called router CNCs) are the most common type of CNC. They either use a flat cutting bit, similar to what you might find on a router, or a cutting tool that resembles a drill bit.

The cutting tool spins at high speeds and then moves through the material (wood, metal, etc.) to shave off layers. This tool moves up, down, left, right, forward, and back, which gives it versatility in the shapes it can create.

If you have any electronics with an aluminum shell, like a cell phone or tablet, chances are a Mill CNC shaped it. Mill CNCs are also used to create rings, coasters, guitar bodies, and more. Essentially, if you could carve it out by hand, you can most likely create it with a mill CNC machine.

Beyond the three most common types of CNC machines, companies also make use of laser, plasma, and water jet cutting machines. But these are more specialized for specific uses, such as cutting down sheet metal.

You Can Own a CNC Machine

A Genmitsu CNC 3018-PRO cutting a shape into pink foam.
Genmitsu

While you might think only large companies can use CNC machines to mass-produce products, that’s not true. CNC printers for the home are becoming more and more common.

Typically, hobbyist CNCs are of the mill variety. Often they use an actual wood router for the cutting tool. They aren’t as powerful and usually can’t work with thick or hard metals.

But home CNC machines are more than capable of working with wood, plastic, foam, and glass. Unlike  with a 3D printer, getting started with a CNC machine is a tedious process.

Most home CNC machines require assembly, and if you don’t pay close attention to what you’re  doing, you might find it doesn’t perform as well as you hoped because of a loose belt or improperly tightened fastener.

And though they are far less expensive than commercial grade CNC machines, consumer devices can still be costly. Small machines with relatively weak motors, like the Genmitsu CNC 3018-PRO, often sell in the $250 range. And larger, more powerful machines like Inventable’s X-Carve will set you back as much as $2,000.

And, much like other woodworking router tools, those only include basic milling bits. You’ll find yourself spending more on specialized carving bits for different types of material (like plywood or acrylic) and which can carve specific shapes.

The average person probably doesn’t need a CNC machine in their home. But if you’re a maker and want to speed up the carving process or create duplicate objects, then you might like a CNC machine for your next tool acquisition.

Josh Hendrickson Josh Hendrickson
Josh Hendrickson has worked in IT for nearly a decade, including four years spent repairing and servicing computers for Microsoft. He’s also a smarthome enthusiast who built his own smart mirror with just a frame, some electronics, a Raspberry Pi, and open-source code. Read Full Bio »

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