HEIDENHAIN TNC 620 (81760x-02) ISO programming - Manual (Page 420)

Programming: Multiple axis machining
12.4 Miscellaneous functions for rotary axes
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TNC 620 | User's ManualDIN/ISO Programming | 2/2015
Selecting tilting axes: M138
Standard behavior
The TNC performs M128, and tilts the working plane, only in those
axes for which the machine tool builder has set the appropriate
machine parameters.
Behavior with M138
The TNC performs the above functions only in those tilting axes
that you have defined using M138.
If you restrict the number of tilting axes with the
M138 function, your machine may provide only
limited tilting possibilities.
Effect
M138 becomes effective at the start of block.
You can reset M138 by reprogramming it without entering any
axes.
Example NC blocks
Perform the above-mentioned functions only in the tilting axis C:
N50 G00 Z+100 G40 M138 C *