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Fanuc lathe 0i: Trouble on constant difference between absolute and machine positions on X-axis after power-on homing.


Jan 31, 2020
Haifa area.

The machine itself is old Lynx 220 from Daewoo. And, more important, it is old "Fanuc i series" with CRT, even "0i" is not mentioned nowhere.
Once APC encoder backup battery was dead, it was replaced.
Draft APZ is performed by manual zero position return for both X and Z - it is shared driver there.

Using lever dial indicator, as usual, "new" X0 was found by going around center-drill body, and new real X homing position (through APZ 0/1 at 1815) was set according to 1240 parameter. It is 290000.
Z-axis homing is completed accordingly.

But, after doing manual ZRN for X-axis, absolute position is 285.111 instead of 290.000. Machine is 290.000.
G54, External reference, tool offset - all are 0.000.

Parameter for Grid Shift 1850 seems not related to this particular shift: changing it for testing an idea from 2776 (it was there) to 0 or to 6000 not helped, even not shows correcting the situation in steps.

Of course, I can shift something to compensate it:
- parameter 1240 to 294890 (not sounds good - it will lead to X-4.890 for center of spindle and for same wrong X in absolute);
- tool offset to -4.890, but just imagine center drill with such X offset?!
- External Reference/G54 - but why zero for X must be shifted if it is not?

Procedure was done twice, both times I got -4.890 difference between absolute and machine.

Searching parameters for something equal 4890, 2445 (1/2) and 9780 (2x) not found nothing.
Machinist of this lathe does not remember how it was looking before battery was dead.

Has anyone any idea how to solve this situations?


Industrial Service Engineer,
I-Vision Mechatronics.