The Fanuc G71 Turning Cycle is a powerful G-code command used in CNC programming for lathes. It’s designed to simplify the process of rough turning by allowing programmers to define a roughing pattern that the machine will automatically repeat.

Usage Format

The basic format for the G71 turning cycle is as follows:

G71 U(Roughing Depth) R(Retract Amount);
G71 P(Start of Profile) Q(End of Profile) U(Finish Allowance in X) W(Finish Allowance in Z) F(Feed Rate);

Explanation

• G71: Initiates the roughing cycle.
• U: Depth of each roughing pass.
• R: Distance the tool retracts from the workpiece in rapid return.
• P: Line number where the profile subroutine starts.
• Q: Line number where the profile subroutine ends.
• W: Amount left on for finishing in the Z-axis.
• F: Feed rate for the cutting process.

Example

Here’s a text diagram and example of how the G71 cycle might be programmed:

O0001 (Program Number)
...
G71 U1.0 R0.5;
G71 P100 Q200 U0.2 W0.05 F0.2;
N100 G00 X45.0 Z1.0;
N101 G01 Z-30.0 F0.2;
N102 X55.0 Z-40.0;
N103 Z-70.0;
N104 X70.0 Z-80.0;
N105 G02 X75.0 Z-85.0 R5.0;
N106 G01 Z-100.0;
N107 X100.0 Z-120.0;
N108 G03 X105.0 Z-125.0 R5.0;
N109 G01 Z-150.0;
N110 X45.0 Z-160.0;
N200 G40 G00 X200.0 Z200.0;
...

In this example, G71 U1.0 R0.5 sets the roughing depth to 1.0mm and the retract amount to 0.5mm. The cycle will repeat the profile defined from N100 to N200, leaving a finish allowance of 0.2mm in X and 0.05mm in Z, with a feed rate of 0.2mm/rev.