Siemens SINUMERIK 840D sl Programming Manual page 111

Traverse rotary axes with path velocity F (FGREF)
For machining operations in which the tool or the workpiece or both are moved by a rotary axis,
the effective machining feedrate is to be interpreted as a path feed in the usual way by
reference to the F value. This requires the specification of an effective radius (reference radius)
for each of the rotary axes involved.
The unit of the reference radius depends on the G70/G71/G700/G710 setting.
All axes involved must be included in the FGROUP command to be taken into account in the
calculation of the path feedrate.
In order to ensure compatibility with the behavior with no FGREF programming, the factor 1
degree = 1 mm is activated on system power up and RESET. This corresponds to a reference
radius of FGREF= 360 mm/(2π) = 57.296 mm.
Note
This default is independent of the active basic system
(MD10240 $MN_SCALING_SYSTEM_IS_METRIC) and the currently active G70/G71/G700/
G710 setting.
Special situations:
Program code
N100 FGROUP(X,Y,Z,A)
N110 G1 G91 A10 F100
N120 G1 G91 A10 X0.0001 F100
NC programming
Programming Manual, 12/2019, 6FC5398-2EP40-0BA0
Fundamentals
2.7 Feed control
111