Siemens SINUMERIK 840Di sl Programming Manual page 136

Motion commands
4.6 Circular interpolation with center point and end point (G2/G3, I=, J=, K=AC...)
Note
G2 and G3 are modal.
The G90/G91 defaults for absolute or incremental dimensions are only valid for the circle
end point.
The center point coordinates I, J, K are normally entered in incremental dimensions with
reference to the circle starting point.
You program the absolute center point non-modally with reference to the workpiece zero
point with: I=AC(...), J=AC(...), K=AC(...). An interpolation parameter I, J, K with value 0 can
be omitted but the second associated parameter must always be specified.
Examples for milling
Incremental dimension
N10 G0 X67.5 Y80.211
N20 G3 X17.203 Y38.029 I–.5 J–.211 F500
Absolute dimensions
N10 G0 X67.5 Y80.211
N20 G3 X17.203 Y38.029 I=AC(50) J=AC(50)
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Programming Manual, 11/2006, 6FC5398-1BP10-2BA0
Fundamentals