In CNC machining, canned cycles are pre-programmed routines that simplify the coding of repetitive machining operations. Fanuc’s G71, G72, and G70 canned cycles are invaluable for lathe operations, particularly for internal machining such as boring and facing. These cycles automate the roughing and finishing processes, enhancing efficiency and precision.

Usage Format

• G71 Rough Turning Cycle:

  G71 U(roughing depth) R(retraction distance);
  G71 P(start of profile) Q(end of profile) U(finish allowance in X) W(finish allowance in Z) F(feed rate);
  

• G72 Facing Cycle:

  G72 W(facing depth) R(retraction distance);
  G72 P(start of profile) Q(end of profile) U(finish allowance in X) W(finish allowance in Z) F(feed rate);
  

• G70 Finishing Cycle:

  G70 P(start of profile) Q(end of profile);
  

Explanation

• G71 is used for rough turning along the Z-axis. It requires defining the depth of each pass, the retraction distance for the tool, and the start and end points of the profile subroutine.
• G72 is similar to G71 but is used for facing cuts towards the centerline of the part on the X-axis.
• G70 is the finishing cycle that follows the same profile defined in G71 or G72, providing a smooth surface finish.

Example

Here’s a text diagram and example of how these cycles might be programmed for a simple internal machining operation:

O0001 (Program number)
...
G71 U2.0 R0.5; (Roughing cycle setup)
G71 P100 Q200 U0.1 W0.1 F0.15; (Roughing cycle parameters)
N100 G00 X50.0 Z5.0; (Start of profile)
G01 Z0.0; (Move to face of part)
X45.0 Z-5.0; (Boring operation)
Z-20.0; (Move to depth of part)
X50.0 Z-25.0; (Finishing cut)
N200 G00 X100.0 Z100.0; (End of profile)
G70 P100 Q200; (Finishing cycle)
...
M30; (End of program)

In this example, G71 initiates a roughing cycle with a depth of 2.0mm per pass and a retraction of 0.5mm. The P100 and Q200 define the start and end of the profile subroutine. The U0.1 and W0.1 set the finishing allowances in X and Z, respectively, with a feed rate of 0.15mm/rev. After roughing, G70 is called to execute a finishing pass over the same profile.