Why does the C axis unwind 180° during retract with G43.4 active?

Community member · DEMO4 days ago2.4k views

On a table-table 5-axis machine, after the finishing operation the C axis suddenly turns 180° in the retract block. TCP is on, the retract plane is defined in machine coordinates inside the post. The same program causes no problem with TCP off.

N840 G1 X-38.204 Y21.418 B-32.0 C42.1 F1180

N850 G0 Z50.

N860 G49

N870 G0 C0.

ATTACHMENTS

MC501_OP20.ncNC snippet · 4 KB

retract_screen.pngMachine screenshot

toolpath_view.pngCAM screenshot

MC501_SETUP.pdfSetup sheet

ACCEPTED SOLUTION

48VOTES

Demo profileCAM / Manufacturing Specialist

The control normalises the C angle to the shortest path during retract. With TCP active this normalisation is reflected as compensation on the linear axes, so the tool rotates while approaching the part. Two-step fix: define the retract plane in part coordinates, and give the unwind in a separate block after TCP is cancelled.

N850 G0 Z50.

N855 G49

N860 G0 C0. (unwind — TCP off)

G43.4 reference DMU 50 kinematics Problem record

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