Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 496)

Tool Tip Radius Compensation (TTRC)
Function
Chapter 21
21-12
If the next programmed move is circular (an arc), position the tool at right
angles to a tangent line drawn from the start-point of that circular move.
Figure 21.9
Tool Path for Entry Move Straight Line-to-Arc
0 £q £ 90 90 £q £ 180
180 £q £ 270 270 £q £ 360
Start-point
Start-point
Start-point
Start-point
Programmed path
Programmed path
Programmed path Programmed path
G41 G41
G42
G42
G41
q
r
r
q
r
r
G41
G42
r
r
q q
G42 r
r
There is no limit to the number of blocks that can follow the programming
of G41 or G42 before an entry move takes place. The entry move will
always be the same regardless of the number of blocks that do not program
motion in the current plane for compensation.