While this guide covers common cases, FANUC and the machine tool builder's original manuals are the ultimate authority. If you lack them, request official documentation before altering parameters.
| Encoder Type | Reference Pulses/Rev | Typical 1820 | Calculated 1860 | |--------------|----------------------|--------------|------------------| | αiA 4096 P/rev | 4096 | 4096 | 1 | | αiB 16384 P/rev | 16384 | 16384 | 1 | | αiCZ 10000 P/rev | 10000 | 10000 | 1 | | βiA 8000 P/rev | 8000 | 8000 | 1 |
| Indicator | Interpretation | |---|---| | Manual skips 1860 | The MTB may be using 1860 for a custom function not covered in base FANUC docs. | | 1860 has non-zero value | The MTB configured it; do not change without documentation. | | 1860 listed same axis format as 1853–1856 | Suggests gear ratio or specialized axis compensation use. |
Fanuc Parameter 1860 is not a "set and forget" value. It is a dynamic tuning lever that balances the competing demands of (cycle time), accuracy (corner fidelity), and stability (vibration-free cutting).
A common symptom of a mis-set 1860 is a "bumping" or "jerky" motion when the axis reverses direction during a G01 move combined with rapid traverse (G00) segments. If you suspect a problem, start by verifying Parameter 1861 as well—the dual position feedback amplitude interacts with the acceleration value.
For most standard CNC lathes and mills using Ball Screws and Flexible Couplings (direct drive or near 1:1 gear ratio):
On many newer Fanuc controls (0i, 31i, 32i), Parameter 1860 is specifically for the reference position.
Press the soft key to open the Handy Setting screen. Move your cursor to the item labeled PARAMETER WRITE . Input 1 and press the [INPUT] key.
, then counter capacity = 4000 pulses. The CNC will think one motor rev = 4000 pulses, causing the reference point to occur twice per physical motor revolution → unstable grid.
This is the most serious consequence. You calculated the shift in the wrong direction.
To truly understand how Parameter 1860 functions in the field, let us walk through a real-world scenario from CNCZone, where a user with a Fanuc 21i-TA lost their machine zero after a servo repair.
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Understanding how this parameter functions is critical for CNC maintenance technicians, builders, and field engineers. Misconfiguring or manually editing this parameter without understanding its behavior can result in axis position discrepancies, reference return issues, or machine damage. Core Definition and Technical Specifications Parameter Structure : 1860
In FANUC CNC systems (such as Series 16i/18i/21i and 0i), Parameter 1860