Fanuc Parameter 1860 -

Cause: Excessively high 1860 causing limit-cycle oscillation near the setpoint.

Solution: Immediately reduce 1860 by 30-40%. If the buzz disappears, re-tune from a lower baseline.

If Parameter 1860 is set too low, the machine accelerates violently. This puts immense stress on the ballscrews, thrust bearings, and servo motors. Over time, this leads to premature mechanical failure, reversed backlash, and accuracy issues.

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. fanuc parameter 1860

Fanuc Parameter 1860 (often listed in manuals as N1860 or PRM 1860) is a position gain parameter specifically associated with the spindle orientation circuit. In simple terms, it tells the spindle drive (usually a Fanuc Alpha i series or earlier digital spindle amplifier) how aggressively to correct positional errors when orienting the spindle to a specific angular position (e.g., 0°, 90°, 180°, or 270°).

More precisely, Parameter 1860 defines the proportional gain (Kp) for the spindle’s position control loop during orientation mode. It is a dimensionless integer value, typically ranging from 0 to 3000, though typical operational values fall between 500 and 2000.

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). | ensure mechanical freedom (check belt

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.

Cause: Spindle cannot reach within the orientation completion width (parameter 1862) due to mechanical binding or incorrect gain. Parameter 1860 might be so low that the spindle never locks.

Solution: First, ensure mechanical freedom (check belt, bearings, drawbar). Then increase 1860 gradually.

"Question about Fanuc parameter 1860 — spindle override low-speed limit. I’m running a slow-boring operation and the spindle won’t go below ~300 RPM despite using spindle override. My machine is a [model]. Any advice on safe values for P1860 or steps to change it? Have already checked for drive limits. Thanks!" fail to find the marker

If you want, tell me the machine model and drive type and I’ll draft a more specific forum post or provide suggested numeric values.

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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).