Understanding FANUC Parameter 1860: A Comprehensive Guide
FANUC, a leading manufacturer of CNC (Computer Numerical Control) systems, utilizes a wide range of parameters to customize and optimize the performance of their machines. One such parameter, often encountered by CNC programmers and machine operators, is parameter 1860. This piece aims to provide an in-depth look at FANUC parameter 1860, its significance, and how it influences CNC machine operations.
| Problem | Likely Cause | Solution | |---------|--------------|----------| | Alarm PS0090 after G28 | 1860 too high → missed marker pulse | Reduce 1860 by 50% and retest. | | Intermittent home position shift (5-20 microns) | 1860 borderline high + electrical noise | Lower 1860; also check encoder cable shielding. | | Axis overtravels immediately after dog detection | 1860 higher than rapid speed (1420) | Set 1860 < 1420. | | Rotary axis homes inconsistently | 1860 too high for rotary inertia | Reduce 1860; consider increasing deceleration time (Parameter 1620). | | Homing takes >5 seconds | 1860 too low | Increase 1860 (test stability first). |
Q1: Can Parameter 1860 be changed while the machine is running?
A: No. Spindle parameters require a power cycle. Changing 1860 without reboot has no effect.
Q2: Does 1860 affect normal spindle speed (Sxxxx) operation?
A: No. 1860 only applies to orientation mode (position control). Speed control remains unaffected. fanuc parameter 1860
Q3: What happens if I set 1860 to zero?
A: The spindle will not orient at all – it may drift or refuse to complete M19. Never set to zero intentionally.
Q4: Why does my OEM recommend a specific number that seems too high?
A: OEMs often set 1860 for maximum stiffness to guarantee tool change reliability, even at the cost of a slight vibration. You can usually reduce it by 10-15% for smoother operation, but confirm with them first.
Q5: Does parameter 1860 exist on Fanuc Robodrill?
A: Yes, on Robodrill with Fanuc 31i-B5. Default is typically 1200 for BT30 spindles.
This is the most common reason technicians look up this parameter. If the acceleration is too aggressive for the load on the axis, the servo motor may not be able to keep up with the commanded position. This frequently results in Servo Alarm 410 (Excess Error in Stop) or Servo Alarm 411 (Excess Error in Moving). The Critical Rule: 1860 < Rapid Speed (1420)
To understand 1860, you must first understand the two-phase homing sequence on a FANUC control:
| Phase | Speed Control | Parameter | Description | |-------|---------------|-----------|-------------| | 1. High-Speed Approach | Rapid traverse (G00) | 1420, 1421, 1422, 1423 | Axis moves toward the deceleration dog at rapid speed. | | 2. Low-Speed Search | Parameter 1860 | PRM 1860 | After hitting the dog, axis decelerates to this speed to find the 1-grid signal (encoder marker pulse). | | 3. Final Stop | N/A (control logic) | N/A | Axis stops at exact reference position (grid point). |
Key Insight: Parameter 1860 sets the creep speed—a slow, precise velocity that allows the CNC to detect the exact rising edge of the position coder's one-revolution signal without overshoot.
If 1860 is set equal to or higher than the rapid speed of that axis, the control will not decelerate properly. The axis may overshoot the dog, fail to find the marker, and trigger alarm PS0090 (Reference return incomplete) or PS0091 (Zero point not found). consult your original machine documentation.
Parameter 1860 is far more than a simple number in a FANUC parameter list. It is a precision tuning tool that balances cycle time against positional repeatability. Too high, and you risk inconsistent homing and alarms. Too low, and you waste seconds on every startup—seconds that add up to hours of lost productivity over a machine's lifetime.
For the CNC engineer, mastering Parameter 1860 means understanding not just the parameter itself, but the entire homing sequence: the rapid approach, the deceleration dog, the marker pulse detection, and the final grid position. When optimized, 1860 delivers a fast, rock-solid reference return that ensures every part starts from the exact same zero point.
Final Recommendation: On any new or unfamiliar FANUC-controlled machine, verify Parameter 1860 as part of your maintenance checklist. Test repeatability annually. A few minutes spent tuning 1860 will pay dividends in consistency and throughput for years to come.
This article applies to FANUC Series 0i, 16i, 18i, 21i, 30i, 31i, 32i, and Power Motion i controls. For specific machine tool builder variations, consult your original machine documentation.
You might wonder, "Why does this specific number matter?" The setting of P1860 directly impacts three critical areas of machine performance:
Parameter 1860 rarely works in isolation. It is part of the acceleration/deceleration profile. You may also need to check: