Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 558)

Cutter Diameter Compensation
(G40, G41, G42)
Chapter 21
21-40
If the control, when scanning ahead, does not find a motion block before
the number of non-motion blocks has been exceeded, it will not generate
the normal cutter compensation move. Instead the control sets up the
compensation move with an end-point one tool radius away from and at
right angles to the programmed end-point.
In many cases, this may cause unwanted over-cutting of a work piece.
Figure 21.36 and Figure 21.37 are example tool paths of programmed
motion blocks followed by too many non-motion blocks before the next
move was made:
Figure 21.36
Too Many Non-Motion Blocks Following a Linear Move
Too many
non-motion
blocks here
Too many
non-motion
blocks here
Too many
non-motion
blocks here
Too many
non-motion
blocks here
End point of compensated
move if not too many non
motion blocks
Compensated
path, G41
Compensated
path, G41
Compensated
path, G42
Compensated
path, G41
Programmed
path
Programmed
path
Programmed
path
Programmed
path
r
r
r
r
r
r
r