Siemens SINUMERIK 840Di sl Programming Manual page 154

Motion commands
4.12 Helical interpolation (G2/G3, TURN=)
Programming the end point for helical interpolation
Please refer to circular interpolation for a detailed description of the interpolation parameters.
Programmed feedrate
For helical interpolation, it is advisable to specify a programmed feedrate override (CFC).
You can use FGROUP to specify, which axes are to be traversed with a programmed
feedrate. For more information please refer to the Path behavior section.
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Programming Manual, 11/2006, 6FC5398-1BP10-2BA0
Fundamentals