Rotary axis unwinds itself during retract
5-axis · retract · C-axis unwind
/en/knowledge/problems/rotary-unwind
QUICK FIX · 45 S
Define the retract blocks in part coordinates and cancel TCP after the retract. Give the C-axis unwind in a separate, controlled block.
WHY IT HAPPENS
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, and the tool rotates while approaching the part.
DEEP DIVE · 8 MIN
When the C axis in the kinematic chain is 360° continuous the control sees no difference between 359° and −1°. The post output gives an absolute angle while the control picks the shortest path; the TCP compensation turns this rotation so as to keep the tool tip fixed. The result is a retract block that looks safe passing over the part.
SOLUTION BY SOFTWARE
Mastercam: define the retract plane per operation in part coordinates, make the unwind a separate operation. NX: match the rotary retract strategy in the post with the clearance geometry. hyperMILL: verify rotary limits and unwind behaviour in the machine definition. Fusion: do not leave the safe retract height in machine coordinates.