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Photo by Bill Ward

Anatomy of a CNC router

For all the attention that 3D printers get in the Maker community, subtractive manufacturing — in this case using a computer numerical control (CNC) router — has a long history of making useful items. Like a 3D printer, it can do its job autonomously, but one should be nearby to stop it if something goes wrong. For those that are unfamiliar with this excellent tool, here’s a quick primer on its parts.

The Spindle is the business end of the CNC router - a high speed rotary tool that holds the cutting bit.

The Spindle is the business end of the CNC router, a high speed rotary tool that holds the cutting bit.

Spindle

Like a non-CNC router, the CNC version uses a cutting bit to remove material. This spindle is commonly a Dremel or other rotary tool, but some are especially sold for this purpose. These can be much quieter, and can potentially be controlled by your computer.

Axis Movement

In order to do anything interesting, the spindle will need to move in the X (left–right), Y (forward–back), and Z (up–down) directions. This is accomplished, in most cases, by a stepper that pushes or pulls the spindle via a a belt or worm gear along a system of rails. Depending on the model, the bed (discussed below) can move instead of the spindle itself in one or more axes.

The Bed is where the cutting happens - and where you will attach your piece to be milled.

The Bed is where the cutting happens, and where you will attach your piece to be milled.

Bed

Whatever you’re working on, be it wood, metal, plastic, or something else, needs a place that can be precisely aligned with the spindle. This is accomplished by something called a “bed,” generally a flat surface where parts can be clamped into place. Clamping can be accomplished by several means, including a vise or other specialized fixtures depending on the work that needs to be done. Some beds also have sacrificial surfaces that can be modified and replaced as needed, including if you happen to make a mistake and drill into it.

This skirt around the cutting bit allows a vacuum to be attached for dust collection.

This skirt around the cutting bit allows a vacuum to be attached for dust collection.

Environment Control

One important addition to many routers is a vacuum nozzle that is attached to the spindle. This can be run while cutting, reducing cleanup time dramatically. Additionally, a box of some sort around the router assembly can cut down on noise, as well as reduce the chance of a broken bit flying dangerously around the room.

The software is what drives the motors of the router and controls the cutting path.

The software is what drives the motors of the router and controls the cutting path.

Computer

Possibly the most obvious element needed for a “computer numerical control” machine is a computer. This computer will need to run a machine control software package, such as Mach3 (or now Mach4) on Windows, LinuxCNC ,Linux, or GRBL Controller, which is cross-platform. Fortunately, the computing power to run this type of software is generally not great, so an appropriate machine can be obtained quite cheaply. A true (not USB) parallel port is required for use with Mach3 software, so an older machine may be advantageous in some cases.

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A gear generated by the Woodgears.ca gear generator being transformed by CamBam into G-Code.

CAD/CAM Software

Machine controller software follows something called “G-Code,” which very literally tells the computer what the router should be doing. Although G-Code can be written by hand, a piece of “Computer Aided Manufacturing” (CAM) software will translate a “Computer Aided Drawing” (CAD) program into something the above listed machine control software can understand.

These programs can range from a few lines of code to thousands upon thousands. If you’re, say, making a model of your face, CAM software is essential. If you’re milling a square or circle, you might be able to get away with writing it by hand.