Siemens SINUMERIK 840D sl Programming Manual page 301

Note
Smoothing cannot and should not replace the functions for defined smoothing (RND, RNDM,
ASPLINE, BSPLINE, CSPLINE).
Smoothing with axial precision with G642
With G642, smoothing does not take place within a defined ADIS range; instead, the axial
tolerances defined with MD33100 $MA_COMPRESS_POS_TOL are applied. The smoothing
clearance is determined based on the shortest smoothing path of all axes. This value is taken
into account when generating a smoothing block.
Block-internal smoothing with G643
The maximum deviations from the precise contour in the case of smoothing with G643 are
defined for each axis using machine data MD33100 $MA_COMPRESS_POS_TOL.
G643 is not used to generate a separate smoothing block, but axis-specific block-internal
smoothing motion is inserted. In the case of G643, the smoothing clearance of each axis can
be different.
Smoothing with contour and orientation tolerance with G642/G643
MD20480 $MC_SMOOTHING_MODE can be used to configure smoothing with G642 and
G643 so that instead of axis-specific tolerances, a contour tolerance and an orientation
tolerance can be applied.
The contour tolerance and orientation tolerance are set in the channel-specific setting data:
SD42465 $SC_SMOOTH_CONTUR_TOL (maximum contour deviation)
SD42466 $SC_SMOOTH_ORI_TOL (maximum angular deviation of the tool orientation)
The setting data can be programmed in the NC program; this means that it can be specified
differently for each block transition. Very different specifications for the contour tolerance and
the tolerance of the tool orientation can only take effect with G643.
Note
Expansion to include contour and orientation tolerance is only supported on systems featuring
the "Polynomial interpolation" option.
Note
An orientation transformation must be active for smoothing within the orientation tolerance.
NC programming
Programming Manual, 12/2019, 6FC5398-2EP40-0BA0
Fundamentals
2.11 Path action
301