Siemens SINUMERIK 840D sl Function Manual page 1866

Detailed Description
2.4 Tool radius compensation 2D (TRC)
Very flat outside corners
Where outside corners are very flat, the response with G450 (transition circle) and G451
(intersection) becomes increasingly similar. In this case, it is no longer advisable to insert a
transition circle. One reason why it is not permitted to insert a transition circle at these
outside corners with 5-axis machining is that this would impose restrictions on speed in
contouring mode (G64). Therefore, the system switches automatically from G450 (transition
circle, with DISC where appropriate) to G451 (intersection) when outside corners are very
flat.
The threshold angle (contour angle) for this automatic switchover (transition circle →
intersection point) can be specified in the machine data:
MD20230 $MC_CUTCOM_CURVE_INSERT_LIMIT (Max. angle for intersection calculation
with tool radius compensation).
Figure 2-31
78
Example of automatic switchover to intersection
Basic logic functions: Tool Offset (W1)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0