How to Simulate Complex 4-Axis and 5-Axis G-Code Programs
Simulating multi-axis CNC programs is not just helpful — it’s critical.
Even a small toolpath error in 5-axis machining can destroy an expensive part or crash a machine.
This guide walks through the key strategies, tools, and challenges in simulating 4-axis and 5-axis G-code.
🌀 Why Multi-Axis Simulation Matters
- 5-axis programs involve simultaneous motion in XYZ + A/B/C rotary axes.
- Errors in postprocessing or CAM setup are harder to detect visually.
- There are more ways a collision can occur (tool, holder, table, head).
- Multi-axis machining often involves tilted planes and tool orientation control.
Simulation gives you a visual, testable safety net before real machining.
🛠️ Recommended Simulation Software
| Software | Type | Features |
|---|---|---|
| Vericut | Paid | Industry standard, full collision detection, machine models |
| NC Simul | Paid | Full kinematics, multi-channel support |
| CAMotics | Free | Basic 4-axis support (limited 5-axis support) |
| Fusion 360 Sim | Built-in | Integrated toolpath preview in Manufacture tab |
| Predator Virtual CNC | Paid | Supports full 5-axis simulation with custom machines |
🔧 Key Features You Should Use
- Tool holder and shank modeling: Catch clearance issues
- Machine kinematics: Make sure rotary motion is within real machine limits
- G68.2 / G43.4 / G234 support: Properly simulate dynamic plane rotation
- Head-table or trunnion setup: Match your real machine’s axis configuration
- Feedrate verification: Detect excessive tool speeds during tilt moves
⚙️ Setting Up the Simulation
- Use a complete postprocessor that outputs correct A/B/C movements
- Import real machine model (STL or native) into the simulator
- Define tool geometry and holder setup
- Import the G-code (NC file) from your CAM
- Run a full simulation and observe:
- Axis limits
- Tilting behavior
- Collision points
- Retracts and linking moves
🧠 Common Mistakes in Multi-Axis Simulation
- Using 3-axis simulator for 5-axis code
- Not modeling the actual tool holder
- Ignoring G43.4 or RTCP (Rotation Tool Center Point) errors
- Assuming CAM preview = real machine motion
- Forgetting to simulate tool orientation in lead/lag angles
📌 Real-World Example
A Fusion 360 post outputs the following for a tilt move:
G43.4 H2 Z100
G1 A45 B30 F500
G1 X50 Y50 Z-10If your simulator doesn’t support G43.4, you’ll miss the actual orientation — a dangerous oversight.
✅ Summary
Simulating 4- and 5-axis G-code isn’t optional — it’s a safety-critical step in high-end CNC.
- Use a simulator that fully supports rotary kinematics
- Verify tool angles, retracts, limits, and actual machine layout
- Detect and fix issues before pressing cycle start
“With multi-axis, what you don’t simulate can cost you thousands.”
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