Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 598)

Using Post Milling Cycles
Chapter 23
23-4
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.
This move takes place at the plunge feedrate specified by the E parameter.
If E is not programmed, the plunge takes place at the roughing feedrate.
After the plunge operation, the control moves the tool in a rectangular
path, defined by the programmed sides of the rectangular post, that starts
and ends at the same point on either the -X or the -Y axis. After
completing a rectangular path, the control makes a single-axis rough cut
along the -X or -Y axis towards the center of the rectangular post. Another
rectangular path is cut that ends at the -X or -Y axis. This process is
repeated until the sides of the post, less the finish allowance H, are
reached.
The width of the first roughing cut is equal to the tool radius. 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.
The tool is then simultaneously raised by the clearance amount and moved
along either the -X or -Y axis at rapid feedrate back to the plunge-position.
This completes machining of one L level.
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 programmed Z depth is reached.
Once the post has been machined out, the control simultaneously raises the
tool to the initial Z level while moving it away from the side of the post by
the clearance amount. This simultaneous move takes place at the rapid
feedrate. The tool is then moved at rapid feedrate along the X, Y, and Z
axes to the pre-cycle position of the tool.
If ,R or ,C is not programmed in the G88.3 block, each corner of the
rectangular post is squared off as much as the tool radius will allow. If ,R
or ,C is programmed in the G88.3 block, the corners of the post will either
be rounded or chamfered. Refer to chapter 16, Using Chamfers and
Corner Radius, for additional information on chamfering and corner
rounding.