Siemens SINUMERIK 840D sl Programming Manual page 286

Tool radius compensation
10.1 Tool radius compensation (G40, G41, G42, OFFN)
In the case of linear movements, the tool travels along an inclined path between the starting
point and end point:
Circular interpolation produces spiral movements.
Changing the tool radius
The change can be made e.g. using system variables. The sequence is the same as when
changing the tool offset data record (D...).
CAUTION
The modified values only take effect the next time T or D is programmed. The change only
applies with effect from the next block.
Compensation mode
Compensation mode may only be interrupted by a certain number of consecutive blocks or M
functions which do not contain drive commands or positional data in the compensation plane.
Note
The number of consecutive blocks or M commands can be set in a machine data item (see
machine manufacturer's specifications).
Note
A block with a path distance of zero also counts as an interruption!
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Programming Manual, 09/2011, 6FC5398-1BP40-2BA0
Fundamentals