Constant cutting speed (G96, G97, G196)

G96 Selection of constant cutting speed (modal) 
G97 Deselection of constant cutting speed, selection of spindle speed (modal, default) 
G196 Maximum spindle speed in the case of G96 (G196 not modal,
max. speed modal) 

Using the G-functions G96, G97 and G196, the interpretation of the S-word (or S-strings) can be optionally changed:

G96 S in m/min (cutting speed )

G97 S in 1/min (spindle speed )

G196 S in 1/min (max. spindle speed during G96)

On selecting G96 the starting rpm of the spindle is given by the programmed cutting speed and the distance of the tool tip to the center point of turning. This distance can be obtained from the last (not in the current NC-block) programmed position and the reference point offset of the face-turning axis. In the current machining plane (G17, G18, G19), exactly one face-turning axis must be present.

A cutting speed programmed for G96 using the S-word is valid only up to the deselection with G97. With G96 the activation of constant cutting speed occurs with the programming of the S-word first.

The specifying of a maximum spindle speed by G196 is optional and effective only during G96.

Close to the center point of turning, the programmed maximum spindle speed (rpm) (G196) or the maximum spindle speed, specified in the assigned axis parameters [2]-17, determines the limits of constant cutting speed.

On deselection with G97, the lastly set spindle speed is maintained.

Traversing blocks of the face-turning axis in the rapid mode (G00) lead to an interruption of G96, thus undesired rpm-value changes while positioning the tool can be prevented. The next traversing block with G01, G02 or G03 cancels the suppression of G96.

Programming example

(X ... Face-turning axis) 
N10 M03 S1000 G01 F1500 X100 
N20 G196S6000 (max. rpm. 6000 1/min) 
N30 G96S63 (Selection of const. cutting speed 63m/min,) 
(Workpiece radius 100mm according to X-coordinates) 
N40 X80 
N50 S4 X50 (New cutting speed 4m/min; workpiece radius 80mm, at) (block end 50mm) 
N60 G97 (Deselection const.cutting speed) 
N70 S8000 (max. rpm. 6000 1/min here not effective!) 
N80 G92 X-10 (Reference point offset in X by -10mm) 
N90 G96X60 (Cutting speed from N50 not valid: const. 
(cutting speed not active, rpm-value 8000 1/min) 
N100 S25 X70 (Cutting speed 25m/min, Workpiece radius 50mm (=60mm+BPV) 
(Const. cuttting speed, active) 
N110 G00 X450 (Rapid mode: rpm-value remains constant) 
N115 X70 
N120 G01 X40 (Suppression of G96 cancelled) 
N110 M30