Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 451)

Programming Feedrates
Chapter 18
18-3
For inside arc paths, the resulting speed of the outside surface of the tool
relative to the part surface would be greater than the programmed feedrate.
Since this could cause excessive tool loading and poor cutting
performance, the control automatically decreases feedrate.
For outside arc paths, the speed of the outside surface of the tool relative
to the part surface can be determined using the following formula:
Rp
Tool surface speed = F x ----
Rc
Where : Is :
F The programmed feedrate
Rc The radius of the arc measured to the center of the tool radius
Rp The programmed radius of the arc
Figure 18.2
Inside and Outside Arc Feedrates with Cutter Compensation
programmed tool path
tool radius center path
Cutting
outside arc
R
c
> R
p
F as programmed
R
c
< R
p
F is reduced
Cutting
Inside arc
R
c
R
p
R
c
R
p
For inside arc paths, the control will automatically maintain the
programmed feedrate at the outside surface of the tool. The actual tool
radius center feedrate will be reduced as needed through the arc path and
then returned to the programmed feedrate after the arc is completed.
During inside arc paths, the control decreases the tool radius center
feedrate by the ratio of Rc/Rp. If the Rc value is very small compared to
Rp, as in the case of a small arc being cut with a large diameter tool, the
value of Rc/Rp will be nearly zero, and the tool radius center feedrate will
become excessively small.