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roughing cycle

The G71 code word on a CNC lathe calls a roughing operation. This is an automated macro-type contouring cycle that is defined by a series of XZ coordinates. The cycle will stay away from the finish size of the part as dictated in the code.

The P word tells the controller number of the first block of the contour
The Q word tells the controller the number of the last block of the contour
The U word says how much stock to leave for finishing in the X direction
The W word says how much stock to leave for finishing in the Z direction
The D word tells how much stock to remove for each roughing pass.
The F word is the feedrate in IPR
The S word is the spindle speed in RPM

N100 G71 P120 Q200 U.06 W.06 D.06 S2000 F.012
N110 G00 XxxxZxxx (rapid to start)
N120 XxxxZxxx (first coordinate of the contour)
N... (multiple block numbers of XxxxZxxx coordinates)
N200 XxxxZxxx (last coordinate of the contour)

Note the red line in the animation represents the "stay away" zone defined by the U and W words. The finish pass shown is not part of the G71 code.