Siemens SINUMERIK 840D sl Programming Manual page 537

FCUB
The feed is approached according to a cubic characteristic from the current feed value to the
programmed F value until the end of the block. The control uses splines to connect all the
feed values programmed non-modally that have an active FCUB. The feed values act here
as interpolation points for calculation of the spline interpolation.
Example:
N50 F1400 FCUB X50
N60 F2000 X47
N70 F3800 X52
Job Planning
Programming Manual, 06/2009, 6FC5398-2BP20-0BA0
8.2 Feedrate response (FNORM, FLIN, FCUB, FPO)
Path traversing behavior
537