Ot Reference Parameter Better ((full)) - Fanuc

This report is structured for maintenance engineers and CNC technicians troubleshooting "Reference Point Lost" alarms (PS/SR 000, 090, 074) or hard overtravel issues after battery failure.

Phase 2: Setting PWE (Parameter Write Enable)

To change anything, you need to unlock the control:

• Press the SYSTEM key (or PARAM on very old panels).
• Scroll to Parameter 0000.
• Set bit 0 (PWE) to 1.
• Warning: The control will immediately flash "P/S 100" alarm (PWE enabled). This is normal. Press RESET once.

4.1 Backlash Compensation (Parameters 1851 & 1852)

On a legacy FANUC 0-T, mechanical wear creates "lost motion" between the motor and the table. fanuc ot reference parameter better

• Action: Measure the actual deviation using a dial indicator or laser interferometer. Update parameter 1851 (normal backlash) and 1852 (rapid traverse backlash) to tighten tolerance bands.
• Benefit: Improves part diameter consistency during direction changes.

Phase 4: The Secret Sauce – Grid Shift (Parameter 0010)

This is the parameter that makes the Fanuc OT better (or worse). Grid shift moves the grid reference point. If your tool changes are inconsistent or your machine doesn't home to exactly the same position every time, your grid shift is wrong.

• Parameter 0010 (bits): JGSX, JGSZ, etc.
• How to optimize: If the machine homes off by 2mm every cycle, don't change the hardware switch; change the grid shift.
  1. Note the current position via Diagnostic 300 (X shift) and 301 (Z shift).
  2. Increment the value in Parameter 0010. Each count moves the grid by one pulse (usually 1 micron or 0.0001 inch).
  3. Better rule: Always adjust grid shift to absorb the backlash. If your screw has .002" backlash, set the grid shift so the final approach is from the same direction every time.

1.0 Executive Summary

This report addresses the concept of "better" parameter referencing for the FANUC Series 0-T control system. The FANUC 0-T is a legacy Turn/Mill control system widely used in industry. While the hardware is robust, machine performance often degrades due to data corruption, battery failure, or improper configuration. This report is structured for maintenance engineers and

A "better" approach to parameter referencing involves moving beyond simple data entry and adopting a strategy of documentation, verification, and optimization. This report outlines critical parameter categories, identifies key parameters for performance enhancement, and provides best practices for parameter management.

4.2 Feed Forward and Servo Tuning

If the machine leaves "grooves" or marks during constant surface speed cycles (G96), the servo loop gains may require tuning. Phase 2: Setting PWE (Parameter Write Enable) To

• Parameter 1825 (Servo Loop Gain): Setting this value correctly ensures the X and Z axes move in perfect synchronization, which is critical for threading and taper turning.

Step-by-Step: How to Set Fanuc OT Reference Parameters Better

Phase 3: Setting the Reference Point Position (Parameters 85 & 86)

This is where "better" happens. Do not set reference to the absolute end of the screw.

1. Jog the machine manually to where you want home to be.
   • X-Axis (Parameter 85): On a lathe, home X is usually at the machine's maximum stroke (e.g., 200mm diameter). Better tip: Leave 5-10mm of unused travel past home. This prevents the nut from hitting the hard stop.
   • Z-Axis (Parameter 86): Home Z is usually just touching the tailstock limit. Better tip: Set it 2mm inside the limit switch trip point to avoid switch bounce errors.
2. On the O-T control, reference point coordinates are set using Machine Position (Absolute value from the pulse coder).
3. Manually write down the Machine Coordinate value from the POS screen.
4. Go to Parameter 85 (X) and 86 (Z). Enter those values.

3.3 Machine Zero Shifted by 0.5 or 1 Pitch of Ball Screw

Cause: Grid shift value is incorrect or the deceleration dog is misaligned.
Fix:

• Calculate new grid shift:
  New_Grid_Shift = Old_Grid_Shift + (Offset_distance / Pitch)
• Example: If zero shifted +0.5mm on a 10mm pitch screw:
  New_Grid = Old_Grid + 500 (in microns, if unit is 1µm).