Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 452)

Programming Feedrates
Chapter 18
18-4
To avoid this problem, the system installer must set a minimum feed
reduction percentage (MFR) in AMP. This will set a minimum feedrate to
be used whenever the value of Rc/Rp is very small. If Rc/Rp control will
reduce the tool radius center feedrate no more than the MFR percentage.
In G93 (inverse time feed) mode, the F--word represents the amount of
programmed axis or axes motion that will be completed in a minute
(moves per minute). For example, if a G93 block were programmed with a
move to X20 (from X0) and a feedrate of 0.2, the X axis would move 0.2
of the move (to X4) in one minute.
Another way of describing this would be to refer to the F--word as the
inverse of the amount of time to complete a programmed move. If it were
desired to complete the move described above in 2 minutes, then the
F--word value would be 1/2 (program 0.5).
If the programmed move is a circular move (G02 or G03 modes), then the
F--word represents the number of radians of the arc or circle to be moved
per minute (radians per minute).
In G93 mode, an F--word is effective only in the block it is programmed (F
is not modal in G93). Therefore, all blocks that call for axis motion when
G93 is active, must contain an F--word or an error occurs.
G93 is modal. It remains active until cancelled by a G94 (feed per minute)
or G95 (feed per revolution).
Figure 18.3
Inverse Time Feed (G93)
Programmed
move
Table
Distance moved in 1 minute
if feedrate (F) value was
0.5 (move per minute)
Cutting
tool
Workpiece
18.1.2
Inverse Time Feed Mode
(G93)