Siemens SINUMERIK 828D Programming Manual page 148

Feed control
7.9 Feedrate optimization for curved path sections (CFTCP, CFC, CFIN)
Further information
Constant feedrate on contour with CFC
148
The feedrate is reduced for inside radii and
increased for outside radii. This ensures a
constant speed at the tool edge and thus at
the contour.
Programming Manual, 07/2010, 6FC5398-1BP40-0BA0
Fundamentals