Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 429)

Programming Feedrates
Chapter 18
18-3
For outside arc paths, the speed of the tool tip relative to the part surface
can be determined using the following formula:
R
p
Tool tip speed = F x ----
R
c
Where : Is :
F programmed feedrate
R
c
radius of the arc measured to the center of the tool radius
R
p
programmed radius of the arc
Figure 18.2
Inside and Outside Arc Feedrates with TTRC
programmed tool path
tool radius center path
Cutting
outside arc
R
c
R
p
R
p
R
c
Cutting
inside arc
R
c
> R
p
F as programmed
R
c
< R
p
F is reduced
For inside arc paths, the control automatically maintains the programmed
feedrate at the tool tip. The actual tool radius center feedrate reduces as
needed through the arc path, and then it returns 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 R
c
/R
p
. If the R
c
value is very small compared to
R
p
, as in the case of a small arc being cut with a large diameter tool, the
value of R
c
/R
p
is nearly zero, and the tool radius center feedrate becomes
excessively small.
To avoid this problem, your system installer must set a minimum feed
reduction percentage (MFR) in AMP. This sets a minimum feedrate to be
used whenever the value of R
c
/R
p
is very small. If R
c
/R
p
< MFR, the
control reduces the tool radius center feedrate no more than the MFR
percentage.