Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 78)

Offset Tables and Setup
Chapter 3
3-4
Tool Diameter Compensation Data (Geometry Table)
To cut a workpiece using the side face of the cutting tool, it is more
convenient to write the part program so that the center of the tool moves
along the shape of the workpiece. Since all cutting tools have a diameter, a
program written for moving the center of the tool must somehow
“compensate” for the tool’s radius.
The system installer determines if radius or diameter values are entered in
the offset table. This manual assumes that the system installer requires
diameter values to be entered.
The control can compensate for this difference using the cutter
compensation feature discussed in chapter 21.
Cutter compensation require that the diameter of the cutting tool be
entered. Call the tool diameter value from the offset tables by
programming a D--word in a part program. Note that the control will
automatically convert the tool diameter to a radius value when necessary.
Tool Length Wear Data (Wear Table)
The tool length wear feature takes into account the wear (change in
length) that the end of a tool will incur from normal usage. Enter a value
in the wear table that is equal to the difference in tool length as entered in
the geometry table and the actual tool length. The value entered as tool
length wear is subtracted from the current value for tool length taken from
the geometry offset table when an H--word is designated in a part program.
This feature allows the compensation for slight changes in tool length
without the need to change the tool geometry table. Then when a worn
tool is replaced with an identical tool the wear offset needs to be reset to
zero. The tool geometry value should never need to be altered once the
initial value is entered as long as identical tools are always used when
replacing tools.
Important: For a typical end milling machine (with tool/chuck
configuration similar to Figure 3.2), keep the following in mind. When
programming tool offsets with a G43, the geometry offset value should be
positive and the wear offset data should be negative when entered in the
offset tables. When programming tool length offsets with a G44, the
geometry offset value should be negative and the wear offset data should
be positive when entered into the offset tables.