Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 372)

Axis Motion
Chapter 14
14-14
Figure 14.7
Automatic Return to Machine Home (G28)
Z
Intermediate point
Machine home
Usually a G28 is followed by a G29 (automatic return from machine
home) in a part program; however, the control stores the intermediate point
in memory for use with any subsequent G29 block executed before power
down. Only one intermediate point is stored for each axis. When a G28 is
programmed with a new intermediate point, any axis not programmed in
that block remains at the old value.
For example:
N1 G28 X4.0 Z3.0; Intermediate point X=4 Z=3
N2 G28 Z2.0; New intermediate point X=4, Z=2
Important: When the control executes a G28 or G30 block it temporarily
removes any tool offsets and cutter compensation during the axis move to
the intermediate point. The offsets and/or cutter compensation are
automatically re-activated during the first block containing axis motion
following the G28 or G30, unless that block is a G29 block. If a G29
follows, the offsets and/or cutter compensation remain deactivated on the
way to the intermediate point and are re-activated when the axis moves
from the intermediate point back to the point indicated in the G29 block.