Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 665)

Milling Fixed Cycles
Chapter 26
26-33
In the G87 back boring cycle, the control moves the axes in the following
manner:
1. The tool rapids to the initial point level above the hole location.
2. After the back boring tool is positioned, the control orients the tool to
a position determined in AMP by the system installer.
The control shifts the boring tool by one of two possible methods, as
discussed below. The shift method is determined in AMP by the
system installer. Refer to the documentation supplied by your system
installer for additional information.
Method I
This shift method is a single axis shift. The direction and axis for the
shift is set in AMP by the system installer or can be altered using the
milling fixed cycle parameter table (see section 26.5).
The direction of the axis is specified as + or -.
The feedrate using this shift method is the programmed feedrate.
The Q--word shift amount is always interpreted as a positive value.
A negative Q--word is not allowed.
Method II
The direction of the shift using this method is programmed in the
boring cycle block. Program a shift amount for axes in the current
plane only (determined by G17, G18, or G19) using the following
words:
I__ programs an X axis move.
J__ programs a Y axis move.
K__ programs a Z axis move.
Follow the I--, J--, and K--words (modal during milling fixed cycles)
with incremental values in the block that programs the hole position.