The Fanuc G73 Pattern Repeating Cycle is a powerful G-code command used in CNC programming to efficiently machine parts with repeating profiles. This cycle is particularly useful for roughing operations on pre-shaped components like castings or forgings, where the contour of the part is already established.

Usage Format

The basic syntax for the G73 command is as follows:

G73 U(W1) W(W2) R(R)
G73 P(Q1) Q(Q2) U(W3) W(W4) F(F)

• U(W1): Depth of cut in the X-axis for each pass.
• W(W2): Depth of cut in the Z-axis for each pass.
• R®: Number of roughing passes.
• P(Q1) and Q(Q2): Start and end line numbers of the profile subroutine.
• U(W3): Finishing allowance in the X-axis.
• W(W4): Finishing allowance in the Z-axis.
• F(F): Feed rate.

Explanation

The G73 cycle is initiated by specifying the depth of cut in both the X and Z axes, along with the number of passes required. The P and Q address letters are used to define the start and end points of the subroutine that contains the profile to be machined. The cycle will repeat the profile defined in the subroutine, stepping over by the amounts specified in U and W after each pass until the roughing is complete.

Example

Here’s a text diagram and example code to illustrate the G73 Pattern Repeating Cycle:

% 
O1000;
T01 M06;
G20 G40 G80 G90;
G00 X1.0 Z0.5 M03 S500;
G73 U0.1 W0.1 R5;
G73 P1000 Q1050 U0.05 W0.05 F0.2;
N1000 G00 X0.5 Z0.1;
G01 Z-1.0 F0.1;
X1.0 Z-1.5;
Z-2.0;
X1.5 Z-2.5;
G02 X2.0 Z-3.0 R0.5;
G01 Z-4.0;
N1050 G00 X4.0 Z0.5;
M30;
%

Text Diagram:

| N1000 | N1050 |
|-------|-------|
|   X   |   X   |
|   |   |   |   |
|   |   |   |   |
|   V   |   V   |

In this program:

• T01 is the tool call.
• G73 U0.1 W0.1 R5 sets the cycle for a 0.1 inch depth of cut in both X and Z axes, with 5 passes.
• P1000 Q1050 points to the subroutine between lines N1000 and N1050.
• The subroutine from N1000 to N1050 defines the profile to be machined.
• U0.05 W0.05 leaves a 0.05 inch allowance for finishing.
• F0.2 sets the feed rate to 0.2 inches per revolution.

This cycle will repeat the profile defined in the subroutine, stepping over by 0.1 inch in both X and Z after each pass, leaving a finishing allowance of 0.05 inch.