Siemens Sinumerik 840D sl Programming Manual page 343

For this type of 3D milling, you require line-by-line definition of 3D paths on the workpiece
surface.
The tool shape and dimensions are taken into account in the calculations, which are normally
performed in CAM. The fully calculated NC blocks are then read into the control via
postprocessors.
Programming the path curvature
Surface description
The path curvature is described by surface normal vectors with the following components:
A4, B4, C4 Start vector at block start
A5, B5, C5 End vector at block end
If a block only contains the start vector, the surface normal vector will remain constant
throughout the block. If a block only contains the end vector, interpolation will run from the
end value of the previous block via large-radius circular interpolation to the programmed end
value.
If both start and end vectors are programmed, interpolation runs between the two directions,
also via large-radius circular interpolation. This allows continuously smooth paths to be
created.
Regardless of the active G17 to G19 level, in the initial setting, surface normal vectors point in
the Z direction.
The length of a vector is meaningless.
Vector components that have not been programmed are set to zero.
With active ORIWKS (see "Reference of the orientation axes (ORIWKS, ORIMKS)") , the
surface normal vectors relate to the active frame and rotate when the frame rotates.
Machine manufacturer
The surface normal vector must be perpendicular to the path tangent, within a limit value set
via machine data, otherwise an alarm will be output.
Job planning
Programming Manual, 02/2011, 6FC5398-2BP40-1BA0
6.2 Three, four and five axis transformation (TRAORI)
Transformations
343