Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 408)

Axis Motion
Chapter 14
14-32
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 reactivated 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 to the point indicated in the G29 block.
When a G29 is executed in a part program (or through MDI) the axis or
axes will move first to the intermediate point, and then to the position
indicated in the G29 block. If a G28 was just executed, then this will have
the effect of returning the axis from machine home. For example,
executing the block:
G29 X7.0 Y.2 Z-14.0 ;
in absolute mode would move the axes to (X7.0, Y.2, Z- 15.0) after passing
through the intermediate point stored in control memory. In incremental
mode this block would move the axes to a position that is X7, Y2, and Z14
units away from the home point.
The intermediate point is stored in control memory after a G28 return to
machine home or a G30 return to alternate home is executed. A G29 block
is usually executed after a G28 or G30 block, typically to return the cutting
tool to the part after a tool change.
Although this command moves the axes at rapid feedrate as if in G00
mode, it is not modal. If G01, G02, or G03 modes are active, they will be
temporarily canceled for the return from home moves.
Only the axes specified in the G29 block are moved. For example:
N1 G28 X5.0 Z1.0; X and Z axes are moved to home after moving to X=5.0, Z=1.0
- - Y is not moved.
N2 G29 X3.; X moves to X=5.0 then to X=3.0
--Y and Z do not move.
Example 14.13
Automatic Return From Machine Home Example
N00010 G00X0.Y50F500;
N00020 X100;
N00030 Y100X150;
N00040 X150.Y50;
N00050 M30;
14.3.3
Automatic Return From
Machine Home (G29)