Siemens SINUMERIK 840DE Programming Manual page 327

With linear movements, the tool travels along an inclined path between the starting point and
end point; with circular interpolation spiral movements are produced.
Changing the tool radius
This can be achieved, for example, using system variables. The execution is the same as for
changes in the D number.
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.
Note
Compensation mode
Compensation mode may only be interrupted by a certain number of consecutive blocks or
M commands, which do not contain any travel commands or positional parameters in the
compensation plane: Standard 3.
Machine manufacturer
The number of consecutive blocks or M commands can be set in machine data 20250 (see
machine manufacturer).
Note
A block with a path distance of zero also counts as an interruption!
Fundamentals
Programming Manual, 10.2004 Edition, 6FC5 298-7AB00-0BP1
8.8 Tool radius compensation (G40, G41, G42)
Tool offsets
8-31