Siemens SINUMERIK 840D sl Function Manual page 1731

Constant speed (G97, G971)
G97, G971 deactivates the "Constant cutting rate function" (G96, G961) and saves the last
calculated spindle speed. With G97, the feedrate is interpreted as a revolutional feedrate (as
with G95).
When programming G971, linear feedrate is selected (as with G94). The feedrate F is
interpreted in mm/min or inch/min.
When G97, G971 is active, an S value can be reprogrammed to define a new spindle speed.
This will not modify the cutting rate programmed in G96, G961.
G97, G971 can be used to avoid speed variations in movements along the transverse axis
without machining (e.g., cutting tool).
Note
G96, G961 is only active during workpiece machining (G1, G2, G3, spline interpolation, etc.,
where feedrate F is active).
The response of the spindle speed for active G96, G961 and G0blocks can be defined in the
channelspecific machine data:
MD20750 ALLOW_G0_IN_G96 (G0 logic for G96, G961)
When constant cutting rate G96, G961 is selected, no gear stage change can take place.
The spindle speed override switch acts on the spindle speed calculated.
A DRF offset in the transverse axis does not affect the spindle speed setpoint calculation.
At the start of machining (after G0) and after NC Stop, G60, G09, ... the path start waits for
"nAct= nSet".
The interface signals "nAct = nSet" and "Set speed limited" are not modified by internal
speed settings.
When the speed falls below the minimum speed or if the signal "Axis/spindle stationary" is
recognized, "nAct =nSet" is reset.
A path operation, which has started (G64, rounding), is not interrupted.
Basic logic functions: Feeds (V1)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.1 Path feedrate F
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