Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 629)

Irregular Pocket Milling Cycles
Chapter 25
25-11
Before invoking the G89.2 cycle, the programmer must activate cutter
compensation left or right by programming G41 or G42. This allows the
control to begin interpreting the blocks that define the contour of the
pocket as they are encountered.
CAUTION: From the start-point the cutter must be able to
move down into the part and then directly over to the start/end
corner of the pocket (A through D in Figure 25.6) without
cutting into any wall of the pocket.
Also, the cutter must be able to move from the end-point of the
P block to the start-point (I through K in Figure 25.7) without
cutting into any wall of the pocket.
The cutter should be positioned at the start-point as described for the G89.1
cycle (A in Figure 25.6). Once the axes are positioned at the start-point, a
plunge along the Z axis takes place. If L is programmed, the tool plunges
along the Z axis to the incremental depth specified by the L parameter
minus the clearance amount (B in Figure 25.6). If L is not programmed,
the tool plunges along the Z axis to the pocket depth specified by the Z
parameter minus the clearance amount (B in Figure 25.6). The plunge
takes place at the rapid feedrate.
After the plunge, the control uses the active cutter compensation mode
(G41/G42) to offset the cutter one cutter radius perpendicular to the line
from the start-point to the start/end corner (C in Figure 25.6). The control
then moves the cutter from this offset position to a point where it is located
one cutter radius plus the finish allowance (if H is programmed) away
from both the first wall of the pocket and the line from the start-point to the
start/end corner. At the same time, the cutter is is lowered the clearance
amount along the Z axis (D in Figure 25.6). This move takes place at the
finishing feedrate.