Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 563)

Cutter Diameter Compensation
(G40, G41, G42)
Chapter 21
21-45
Change in Cutter Radius During Jog Retract
This section describes a change in the cutter radius during a jog retract
operation. This is a typical operation since the jog retract feature is often
used when a tool becomes very worn or is broken. It may be necessary to
replace the tool with a tool of a slightly different diameter. Cutter
compensation is able to adjust to the new tool diameter.
Typically when the jog retract operation is performed, the tool is jogged
away from the workpiece and then replaced. After it is replaced, it is
necessary to activate a different tool diameter offset value. This is
typically done in either of two methods:
The new offset number is activated by programming a new D word in
an MDI block.
The new offset number is activated by using the {ACTIVE OFFSET}
softkey found on the offset table screen. This feature is discussed in
chapter 2.
However the new offset is activated, cutter compensation is able to
compensate for this new diameter by modifying the saved jogged path.
This path is modified so that the new tool will cut the same part as the old
tool. The absolute position of the machine, therefore, is different on the
return path from what it was when jogging away from the part.
This jogged path is adjusted when the button is pressed to return from the
jog retract. As soon as the <CYCLE START> button is pressed, the
control generates a move that offsets the current tool position by the
necessary distance. This distance is determined as being the necessary
distance the tool would have to be positioned at so that the exact same jog
return paths can be used to return to the part and yet have the end-point be
offset from the original position by the difference in the cutter diameter.
CAUTION: Make sure that this offset path will not cause any
collisions with the part or the machine fixtures. The position of
the tool, when the tool change in jog retract is made, should be a
safe distance from the part and machine fixtures.