| Machine Type | Rigidity | Typical 1860 Range (ms) | | :--- | :--- | :--- | | Small VMC (BT30) | High | 30–60 | | Large VMC (BT40/BT50) | Medium | 60–120 | | Heavy-duty lathe (X-axis) | Medium | 80–150 | | Gantry mill (heavy slide) | Low | 120–250 | | High-speed machining center | Very High | 10–40 |
| Problem | Cause | |---------|-------| | Alarm PS0030 or PS0031 | 1860 set too high → reference point signal missed due to overshoot | | Inconsistent reference position (drift every cycle) | Speed too high for deceleration zone length (dog/switch timing mismatch) | | Long cycle time | 1860 set unnecessarily low (e.g., 100 mm/min on a large VMC) | | Machine overshoots reference point | 1860 > rapid rate (not allowed; parameter clamped internally) |
The relationship between time constant (T) and acceleration (a) is:
a (mm/s²) = Vc / T
Where:
Example:
Real-world adjustment: Most machines will not run a 10 ms 1860 due to mechanical resonance. Multiply by 3–5x for safety (e.g., 40–60 ms).
If Parameter 1860 is set incorrectly (e.g., after a servo swap or battery backup loss), the following issues will occur:
Threading Failures (Lathes):
Servo Alarm (Invalid Parameter):
Your Fanuc servo system operates on a "Grid" generated by the position feedback device (pulse coder, absolute encoder, or scale). As the motor rotates, the encoder sends pulses. The control identifies a specific pulse as the "Grid Point" – a reproducible position for machine zero.
When you adjust Parameter 1860, you are not moving the physical limit dog. You are electronically shifting where the control thinks the grid point is.
The formula is conceptual:
Final Grid Position = Natural Grid Point + Value(Parameter 1860) fanuc parameter 1860 full
There is no universal "perfect" number for 1860. It depends on your machine's mechanical design, motor torque, and the workpiece material. However, you can calculate a safe starting point.
Technicians often confuse 1860 with other parameters. Here is a clear comparison:
| Parameter | Function | When Active | Typical Range | | :--- | :--- | :--- | :--- | | 1860 | Cutting feed ACC/DEC time constant | G01, G02, G03 | 20–200 ms | | 1620 | Rapid traverse (G00) ACC/DEC time constant | G00 | 50–500 ms | | 1622 | Rapid traverse DEC time constant (linear) | G00 (end of move) | 0 (off) to 500 ms | | 1825 | Servo loop gain (Position loop gain) | All motions | 30–200 (1/sec) |
Critical Insight: Parameter 1860 and Parameter 1825 (position loop gain) work in tandem. If you increase 1825 for higher stiffness, you may need to decrease 1860 to avoid instability. Conversely, a low 1825 with a very low 1860 will cause overshoot. | Machine Type | Rigidity | Typical 1860