Fanuc G72.1 G72.2 Figure Copy Program Example (Bolt Hole Circle)

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In CNC programming, precision and repetition are key for creating complex geometries with high accuracy. Fanuc’s G72.1 and G72.2 figure copy functions are powerful G-codes used to replicate shapes in a rotational or linear pattern, respectively. This article will delve into these G-codes, particularly looking at their application in programming a bolt hole circle.

Usage Format

The usage format for the G72.1 (Rotational Copy) and G72.2 (Linear Copy) commands is as follows:

  • G72.1G72.1 P... X... Y... L... R...
  • G72.2G72.2 P... X... Y... L...

Where:

  • P is the subprogram number that defines the shape to be copied.
  • X and Y are the center coordinates for rotation or the direction of linear copy.
  • L is the number of times the shape is to be copied.
  • R (only for G72.1) is the angle of rotation.

Explanation

G72.1 Rotational Copy is used when you want to duplicate a figure around a center point at specified angular increments. It’s ideal for circular patterns like bolt hole circles.

G72.2 Linear Copy allows for the duplication of a figure along a straight line, which is useful for drilling rows of holes or milling slots.

Both commands require a subprogram that defines the figure to be copied. It’s important to note that G72.1 cannot be specified more than once in a subprogram for making a rotational copy, and similarly, G72.2 cannot be specified more than once for a linear copy.

Example

Let’s consider a bolt hole circle example using both G72.1 and G72.2:

Main Program:

O1000 ; Main program start
G90 G17 G40 G49 G80 ; Absolute positioning, XY plane, cancel modal commands
G0 X0 Y0 ; Move to the center of the bolt hole circle
G72.1 P2000 X0 Y0 L8 R45. ; Call subprogram P2000, 8 holes, 45-degree increments
G80 ; Cancel canned cycle
M30 ; End of program

Subprogram for Bolt Hole Circle (P2000):

O2000 ; Subprogram start
G81 G98 Z-10 R2 F75 ; Drilling cycle, retract to R-plane, feedrate
X20.0 ; First hole position
G80 ; Cancel drilling cycle
M99 ; Return to main program

Text Diagram:

      Y+
      |
      |     O O O
      |      \|/
X- ——+—— O—+—O —— X+ (Center point at +)
      |     /|\
      |     O O O
      |
      Y-

In this example, the subprogram O2000 defines a single hole to be drilled. The main program O1000 uses G72.1 to rotate this hole around the center point (X0 Y0) to create a bolt hole circle with 8 holes at 45-degree increments.

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