Siemens Sinumerik 840D sl Programming Manual page 203

Examples
Example 1: Counter-clockwise involute from the starting point to the programmed end point
and back again as clockwise involute
Program code
N10 G1 X10 Y0 F5000
N15 G17
N20 INVCCW X32.77 Y32.77 CR=5 I-10 J0
N30 INVCW X10 Y0 CR=5 I-32.77 J-32.77
...
Fundamentals
Programming Manual, 01/2015, 6FC5398-1BP40-5BA2
10.8 Involute interpolation (INVCW, INVCCW)
Comment
; Approach the starting position.
; Selection of the X/Y plane as
working plane.
; Counter-clockwise involute, end
point in Cartesian coordinates.
; Clockwise involute, starting
point is end point from N20, new
end point is starting point from
N20, new circle center point refers
to a new starting point and is the
same as the old circle center point.
Motion commands
203