G68 and G69 Explained: Rotating Coordinate Systems in CNC Programming

G68 and G69 Explained: Rotating Coordinate Systems in CNC Programming

Need to machine angled slots, holes, or features without using a CAM system?

Use G68 to rotate your coordinate system and G69 to reset it.

This guide shows:

• What G68 and G69 do
• Syntax and parameters
• How to rotate around a point
• Real-world use cases for angled machining
• Safety considerations and best practices

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🔄 What Is G68?

G68 rotates the active coordinate system around a defined point and axis.

Instead of rotating the part, you rotate the XY coordinate grid, so that straight G-code moves appear at an angle.

🧠 Why Use G68?

• Machine features at 45°, 60°, or custom angles
• Avoid complex CAM operations
• Simplify code reuse for angled parts

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🟢 G68 Syntax

📘 2D Rotation in XY Plane:

G68 X__ Y__ R__

Code	Meaning
X/Y	Rotation center point
R	Rotation angle in degrees

📘 Example:

G68 X0 Y0 R45  ; Rotate coordinate system 45° around (0,0)
G1 X100 Y0     ; Actually moves along 45° diagonal

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🚫 G69 – Cancel Rotation

Use G69 to return to the normal coordinate system after you’re done.

G69   ; Cancel rotation

Always use this to prevent unintended behavior in the next operations.

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🔁 How It Works (Visual)

• Normally, G1 X50 Y0 moves right.
• With G68 X0 Y0 R45, the same line moves diagonally (northeast).
• You’re not rotating the part — just the coordinate grid.

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🧪 Practical Example – Slot at 60 Degrees

G54
G0 X0 Y0
G68 X0 Y0 R60     ; Rotate 60° around origin

G1 X50 Y0 F200    ; This will cut along a 60° line
G1 X0 Y0

G69               ; Reset coordinate rotation

✅ Same G-code can be reused for multiple angles by just changing R value.

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📏 Use Case: 4 Holes at 45° from Center

G68 X0 Y0 R45
G81 R2 Z-10 X20 Y0 F150
G68 X0 Y0 R135
G81 R2 Z-10 X20 Y0 F150
G68 X0 Y0 R225
G81 R2 Z-10 X20 Y0 F150
G68 X0 Y0 R315
G81 R2 Z-10 X20 Y0 F150
G69

Instead of calculating X/Y manually for each hole, we reuse same position with rotated axes.

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⚠️ G68/G69 on 3-Axis Machines

• Only rotates in XY plane by default (Z is unaffected)
• Some controls support 3D rotation with G68.2 (Fanuc 31i, Siemens)
• Not available on all controls — check your machine!

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🔐 Safety Tips

Tip	Why
Always reset with G69	Prevent unintended rotated moves
Simulate rotated moves	Avoid confusion or crash
Use comments generously	Improve future debugging
Avoid G68 inside subprograms	Unless fully controlled/reset

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🧩 Summary Table

Code	Function
G68	Rotate coordinate system
G69	Cancel rotation
R	Rotation angle (degrees)
X/Y	Center of rotation

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💡 Pro Tips

• Combine G68 with G52 temporary offsets for advanced setups
• Great for angle repeat features on fixtures or rotary tables
• Use in macro programs to create dynamic part families

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📚 Advanced: Combining G68 with Subprograms

G68 X0 Y0 R30
M98 P1000
G68 X0 Y0 R60
M98 P1000
G68 X0 Y0 R90
M98 P1000
G69

This runs the same pattern 3 times at 30°, 60°, and 90° rotations.

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🧠 Conclusion

G68 and G69 allow powerful control of machining angles without rotating your part or rewriting code. When used correctly, they make your G-code modular, reusable, and incredibly efficient.

“Why rotate the part, when you can rotate the world around it?”

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✅ Next Suggested Topic:
“Using G10 for Programmatic Work Offsets and Tool Data Input”