Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 519)

Tool Tip Radius Compensation (TTRC)
Function
Chapter 21
21-35
The following subsections describe possible tool paths that can be
generated when programming one of the following during TTRC:
changing TTRC direction (cross-over tool paths)
exceeding the allowable number of consecutive, non-motion blocks
during TTRC
corner movement following a generated block
changing cutter radius during TTRC
effect on TTRC when interrupting a program to execute either a MDI
program or a manual move
changing or offsetting current work coordinate system during TTRC
moving to and from machine home and secondary machine home
This section describes the resulting tool path when a change in
compensation direction (left or right) is programmed. This can result in
the cutting tool crossing over the programmed tool path as compensation
changes from left to right or right to left.
Linear Tool Path-to-Linear Tool Path.
The following figures show the tool path taken when TTRC is changed
from G41 to G42 during the execution of two linear program moves.
The control generates two points when changing TTRC direction: point 1
and point 2.
Point 1 is the final tool position before compensation direction is
changed (at right angles to the end-point of the programmed tool path
offset by one tool radius)
Point 2 is the desired tool position for the start of the first block using
the changed compensation direction (at right angles to the start-point of
the motion block that changes compensation direction and offset by the
tool radius)
21.6
TTRC Special Cases
21.6.1
Changing TTRC Direction