Fanuc Parameter 8901 Better Page

Assuming a typical linear axis with a 1,000,000 pulse/rev encoder (nanoscale resolution):

Step 1: Set Parameter 8901 = 10010001 binary (bits 7, 4, and 0 = 1)

Step 2: Set Parameter 1850 (Grid Shift amount) to a small positive integer, e.g., 20 (pulses).
With 8901.0=1, this value now represents a fine offset from the index pulse rather than from the dog.

Step 3: Set Parameter 1821 (Reference position) as usual. fanuc parameter 8901 better

Step 4: Test reference return 10 times and measure repeatability using a dial indicator or laser.

For rigid tapping, the spindle must follow the linear axis moving the tap. That is always Z on a mill, always Z on a lathe (axial tapping), or Y on a lathe (radial tapping).

Better rule: Never set 8901 to the default X or Y if Z is available. Use the highest-number axis that matches the tap feed axis. Assuming a typical linear axis with a 1,000,000

A: Check Parameter 1401 (bit 6). Your machine may lack the "AICC II" option. Fanuc sells this as a paid software option (DNC operation or High-speed machining package). If you haven't purchased the option, the machine will alarm. You cannot "hack" 8901=2 without the license.

If you’ve decided to make Fanuc Parameter 8901 better, follow these steps carefully. Note: Changing this parameter will affect all active and future tool offsets. Plan this change during a downtime or between jobs.

Note: This parameter works in conjunction with memory backup batteries. If parameter 8901 is set, it flags the SRAM area for work offsets as "protected/retained," ensuring that volatile memory keeps the G54 data alive during a controlled power-down, preventing the dreaded "0030 Power-off without memory backup" alarms or data clearing. Step 2: Set Parameter 1850 (Grid Shift amount)

| Bit | Function | 0 (Conventional) | 1 (Better / Advanced) | |-----|----------|------------------|------------------------| | 0 | Reference return method | Uses deceleration dog + grid | Dogless reference return (uses just index pulse or marked point) | | 1 | Grid shift direction | Positive grid shift | Negative grid shift (allows finer compensation) | | 2 | Multiple grid shift | Disabled | Enabled for axes with multiple reference positions | | 3 | External deceleration signal | Required | Ignored (dogless) | | 4 | High-speed reference return | Standard speed | High-speed search of index pulse | | 5 | Marked point detection | Disabled | Enabled (for absolute encoders) | | 6 | Manual reference return compensation | Off | On (adjusts for thermal growth) | | 7 | Backup grid shift | Off | On (stores last valid grid) |

Most important for “better” performance:

Mistake 1: Changing 8901 without clearing old grid shift values.
→ Fix: After changing 8901, power off/on, then perform reference return twice.

Mistake 2: Setting 8901.0=1 but leaving 1850 too large (e.g., >1000).
→ Fix: Keep 1850 between 1–100 for most encoders.

Mistake 3: Forgetting to set parameter 1815.4 (APZ) to 0 then 1 after grid shift change.
→ Fix: Always re-establish reference position after changing 8901.