Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 535)

Cutter Diameter Compensation
(G40, G41, G42)
Chapter 21
21-17
If the last programmed move prior to the exit move (which must be linear)
is circular (an arc), the tool is positioned at right angles to a tangent line
drawn from the end-point of that circular move.
Figure 21.13
Tool Path for Exit Move Arc-to-Straight Line
Programmed path
End-point End-point
90
• • •
180 0
• • •
90
180
• • •
270 270
• • •
360
Programmed path
Programmed path
Programmed path
G42
G41
End-point
End-point
G42
G41
G42
G41
• •
•
•
r
r
r
r
r
r
r
r
G41
G42
The above examples in Figure 21.12 and Figure 21.13 assume that the
number of blocks that do not contain axis motion in the current plane,
following the programming of G40 before an exit move takes place, does
not exceed an amount selected in AMP by the system installer. If the
number of non-motion blocks following G40 exceeds the limit, the control
generates its own exit move. This may often cause over-cutting of the part.
It is possible to modify the path that the tool takes for an exit move by
including an I, J, and/or K word in the exit move. Only the I, J, or K
words that represent values in the current plane are programmed in the
block containing the exit move. I, J, and K correspond to the X, Y, and Z
axes respectively.