G72 Facing Cycle Explained for CNC Lathes

The G72 Facing Cycle is an important programming command that is widely used in CNC lathes. This command smooths the surface of the workpiece by removing material to a certain depth.

G72 is a very useful facing cycle, especially for circular profiles and medium-hard materials. It completes the facing operation by repeating the programmed tool path automatically through loops.
The biggest advantage of G72 is that you don’t need to write the same commands again and again, which saves time and reduces programming errors.

What is the G72 facing cycle?

To use G72, you give the X and Z coordinates in the program, and the machine removes the material to the desired level. This command is especially useful for production work. It saves time and reduces the room for error during machining. By using this command, the surface of the workpiece becomes smooth and accurate. That is why this command is used as a basic and effective tool in the CNC lathe program.

G72 Facing Cycle Rough Facing

G72 W R;

G72 P Q U W F;

First G72 line

W = Depth of cut in Z direction (negative value)

R = Retract amount (tool pull-back after each cut)

Second G72 line

P = Starting block number of profile

Q = Ending block number of profile

U = Finishing allowance in X

W = Finishing allowance in Z

F = Feed rate

G72 Simple Program example

G00 X120 Z2
G72 W-2.0 R1.0

G72 P10 Q20 U0.3 W0.2 F0.25

N10 G00 X120 Z0
N20 G01 X0

G00 X120 Z2

X120 = outside diameter

Z2 = 2 mm in front of the face

G72 W-2.0 R1.0

W-2.0 → Depth of cut in Z direction (2 mm per pass, negative because facing goes toward Z0 / minus Z)

R1.0 → Retract amount (tool pulls back 1 mm between passes)

G72 P10 Q20 U0.3 W0.2 F0.25

P10 → Start of profile block (N10)

Q20 → End of profile block (N20)

U0.3 → Finishing allowance in X

W0.2 → Finishing allowance in Z

F0.25 → Feed rate

N10 G00 X120 Z0

Rapid to the outer diameter at the face

N20 G01 X0

End block