Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 579)

Using Pocket Milling Cycles
Chapter 22
22-7
If L is programmed, the tool plunges along the Z axis to the incremental
depth specified by the L parameter. If L is not programmed, the tool
plunges along the Z axis to the pocket depth specified by the Z parameter.
The plunge takes place at the plunge feedrate specified by the E parameter.
If E is not programmed, the plunge takes place at the roughing feedrate
specified by the F parameter.
After the plunge operation, the control performs a single-axis cut outwards
to a point on the longest side of the rectangular pocket. This move is
always along the -X or -Y axis depending on whether the rectangular
pocket is longer along the X or Y axis (shorter axis move is the first
move). The control then moves the tool in a rectangular path that starts
and ends at either the -X or -Y axis.
This process is repeated until the sides of the enlarged pocket, less the
finish allowance H, are reached. The tool is then raised by the clearance
amount and moved at rapid feedrate back to the plunge- position. This
completes the machining of one L level.
The width of the last roughing cut is equal to the tool radius plus the finish
allowance (H + TR). The width of the remaining roughing cuts is
calculated by the control based on the remaining area to be roughed-out
and the programmed rough cut thickness, D. The control divides the
remaining area by D to calculate the number of roughing cuts needed to
rough out this area. The control then adjusts the width and number of
these cuts until an even number of roughing cuts is achieved. The width of
these cuts will always be equal to or less than the programmed rough cut
thickness, D.
If the programmed Z depth of the pocket has not been reached, another
plunge along the Z axis to the next L level takes place. This level is then
machined as described in the previous paragraphs. This process is repeated
until the pocket is machined out.
Once the pocket has been machined out, the control simultaneously raises
the tool to the initial Z level plus the clearance amount while moving it
away from pocket edge by the clearance amount. This simultaneous move
takes place at the rapid feedrate. The tool is then moved at rapid feedrate
simultaneously along the X, Y, and Z axes to the pre-cycle position of the
tool.
If ,R or ,C is not programmed in the G88.1 block, each corner of the
rectangular pocket is squared off as much as the tool radius will allow. If
,R or ,C is programmed in the G88.1 block, the corners of the rectangular
pocket will either be rounded or chamfered. Refer to chapter 16, Using
Chamfers and Corner Radius, for additional information on chamfering
and corner rounding.