Understanding CNC File Formats: G-Code, TAP, NC, and More Explained

Understanding CNC File Formats: G-Code, TAP, NC, and More Explained

CNC machining revolves around precise instructions delivered to machines in the form of code files. These files vary in extension and structure based on the controller type, CAM software, and machine configuration.

In this guide, we’ll break down the most common CNC file formats, what they contain, and how to ensure compatibility across different systems.

---

📂 Common CNC File Extensions and Their Uses

Extension	Meaning	Typical Use	Example Controllers
.gcode	G-code	Standard CNC program	Marlin, GRBL, RepRap
.nc	Numeric Control	Generic G-code programs	Fanuc, Haas, Siemens
.tap	Tapping file	Often used in routers/plasmas	Mach3, Torchmate
.txt	Text file	Universal, editable format	All controllers
.eia	EIA compliant	Aerospace/military machines	Older legacy systems
.min	Minimal G-code	Specialized CAM exports	Heidenhain

---

🧠 What’s Inside a CNC File?

Example of a .nc file content:

%
O1001
G21 G90 G17
G0 Z5
G0 X0 Y0
G1 Z-2 F150
G1 X100 Y0 F300
G1 Y50
G1 X0
G1 Y0
M30
%

Each line performs an action:

• G21 = metric units
• G90 = absolute positioning
• G1 = linear interpolation
• M30 = end of program

---

🆚 File Format Differences: GCODE vs NC vs TAP

Feature	.gcode	.nc	.tap
Readable by all editors	✅	✅	✅
Contains tool info	Sometimes	Yes	Yes
Machine-specific format	Usually yes	Yes	Yes
Editable by hand	✅	✅	✅
CAM software output	Yes	Yes	Yes

---

🧰 How CAM Software Affects File Format

CAM programs like Fusion 360, Mastercam, SolidCAM, or VCarve export CNC files based on:

• Postprocessor selected
• Machine definition
• Toolpaths created

Postprocessors are the key. They control how G-code is generated:

• Fanuc-style vs Siemens-style
• Custom G/M-code mappings
• Header/footer differences

You can modify postprocessors to match your controller.

---

🛠️ Tip: Converting Between File Types

You can rename extensions manually in many cases:

• program.gcode → program.nc
• part.tap → part.txt

However, make sure the internal syntax matches your machine’s dialect.
Use CAM software or a G-code editor to validate before sending to your controller.

---

📦 File Format Compatibility Chart

Controller Brand	Accepts .gcode	Accepts .nc	Accepts .tap
Marlin/GRBL	✅	✅	❌
Fanuc	✅	✅	✅
Mach3	✅	✅	✅
Haas	✅	✅	✅
Siemens	✅	✅	❌
Heidenhain	❌	✅	❌

---

💡 Pro Tips

• Always simulate first using a G-code viewer like CAMotics or NC Viewer
• Use consistent naming conventions: ProjectName_Material_ToolNumber.nc
• Backup your original CAM projects in case you need to regenerate G-code
• Store your postprocessor settings per machine

---

✅ Summary

Understanding the differences between .gcode, .nc, .tap, and other CNC formats allows you to:

• Match files to the correct machine
• Prevent costly syntax errors
• Customize and optimize toolpaths
• Ensure safety and accuracy

“Know your format. Know your machine. Know your outcome.”

---

▶️ Next Topic: CNC Job Market — Career Paths, Global Demand, and Certifications