What is CNC?
CNC stands for Computer Numerical Control. It's a method of automating machine tools using programmed commands rather than manual operation.
A CNC router is essentially a computer-controlled cutting machine. You design something on a computer, the software converts it into movement instructions (called G-code), and the machine follows those instructions to cut your design from wood, plastic, metal, or other materials.
Think of it like this: A CNC router is to a handheld router what a printer is to a pen. You tell it what you want, and it executes with precision and repeatability.
How a CNC Router Works
A typical hobby CNC router has these main components:
- Frame/Gantry: The structure that holds everything together and moves
- Spindle/Router: The motor that spins the cutting tool
- Stepper Motors: Motors that move the gantry with precise control
- Controller: The electronics that interpret commands and drive the motors
- Bed/Wasteboard: The surface you mount your material on
The machine moves in three directions:
The Coordinate System
CNC machines use a Cartesian coordinate system with X, Y, and Z axes:
- X-Axis
- Left and right movement (typically the longest axis on a router)
- Y-Axis
- Front and back movement
- Z-Axis
- Up and down movement (controls cutting depth)
Work Zero vs Machine Zero
Machine Zero is a fixed point—usually the home position of the machine (often front-left corner when homed).
Work Zero (also called "work origin" or "job zero") is a point YOU set that tells the machine where your material starts. This is typically set at a corner of your workpiece or the center, depending on your CAM setup.
Critical concept: Before every job, you must set your work zero. If you don't, the machine has no idea where your material is and will cut in the wrong place (or into your bed).
Z-Zero Location
Z-zero can be set at two places:
- Top of material: Most common. Z=0 is the surface of your workpiece. Cuts go into negative Z.
- Top of wasteboard: Z=0 is the bed surface. Your material thickness is in positive Z. Less common but useful for through-cuts.
Essential Terminology
- G-code
- The programming language that tells CNC machines how to move. Commands like G0 (rapid move), G1 (linear cut), G2/G3 (arcs). Your CAM software generates this automatically.
- CAD (Computer-Aided Design)
- Software for creating designs. Examples: Fusion 360, SketchUp, Inkscape, Adobe Illustrator.
- CAM (Computer-Aided Manufacturing)
- Software that converts designs into G-code toolpaths. Examples: VCarve, Fusion 360 CAM, Carbide Create, Aspire.
- Toolpath
- The path the cutting tool follows to create your design. Different operations (pocket, profile, engrave) create different toolpaths.
- Feed Rate
- How fast the tool moves horizontally through material (inches per minute or mm per minute).
- Plunge Rate
- How fast the tool moves down into material (Z direction). Usually much slower than feed rate.
- Spindle Speed (RPM)
- How fast the cutting tool rotates. Higher isn't always better—it depends on the tool and material.
- Depth of Cut (DOC)
- How deep each pass cuts. Multiple shallow passes are safer than one deep pass.
- Stepover
- For pocketing operations, how much the tool moves over between passes. Usually 40-50% of tool diameter.
- Chipload
- The thickness of material each cutting edge removes per revolution. The key to good cuts. Learn more →
Tooling Basics
The cutting tool (called an "end mill" or "bit") is what actually removes material. Common types:
End Mills
- Flat End Mill: Flat bottom, for pockets, profiles, and general cutting
- Ball Nose: Rounded tip, for 3D carving and smooth contours
- Upcut: Pulls chips up, great chip clearing, may cause tearout on top surface
- Downcut: Pushes chips down, clean top edge, may pack chips in deep cuts
- Compression: Upcut bottom + downcut top, clean edges on both faces
V-Bits
Angled cutting tools for engraving, chamfers, and V-carving text. Come in various angles (30°, 60°, 90°).
Flute Count
Flutes are the cutting edges on the tool.
- 1 flute: Best chip clearance, for plastics and aluminum
- 2 flute: Good all-around, most common for wood
- 3+ flute: Smoother finish, requires faster feed rates
The CNC Workflow
- Design — Create or import your design in CAD software
- CAM Setup — Define toolpaths, select tools, set feeds/speeds
- Generate G-code — Export the toolpaths as a .nc or .gcode file
- Machine Setup — Mount material, install tool, set work zero
- Verify — Review G-code in a simulator or viewer
- Run — Send G-code to machine, monitor the cut
- Finish — Remove part, sand, finish as needed
Pro tip: Always simulate or visualize your G-code before running it on the machine. Our free G-code Viewer lets you see exactly what the machine will do.
Common Beginner Mistakes
1. Not securing the workpiece
If your material moves during cutting, the job is ruined (and possibly dangerous). Use clamps, screws, tape + CA glue, or vacuum hold-down. Test that it won't budge.
2. Wrong Z-zero
Setting Z-zero incorrectly means cutting too deep (into your wasteboard) or too shallow (not cutting through). Double-check before every job.
3. Using manufacturer speeds without testing
Manufacturer recommendations assume industrial machines. Your hobby CNC may need different settings. Always test on scrap first. Use our feed/speed testing tool to dial in proper parameters.
4. Too aggressive depth of cut
Trying to cut too deep in one pass causes tool deflection, chatter, poor finish, and broken bits. Start with shallow passes (1/2 tool diameter max for most materials).
5. Ignoring chip clearing
Chips that aren't cleared get re-cut, generating heat and wearing your tool. Use dust collection or air blast, especially in deep pockets.
Safety first: Always wear safety glasses. Use hearing protection. Never leave a running machine unattended. Keep hands away from the spindle. Have an emergency stop within reach.
Next Steps
Now that you understand the basics:
- G-code Reference — Learn the commands that control your machine
- Learn Feeds & Speeds — The most important skill for good cuts
- Understand Chipload — Why it matters and how to calculate it
- Try the Testing Tool — Dial in your first bit with guided testing
- Use the G-code Viewer — Visualize files before cutting