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:
- G72.1:
G72.1 P... X... Y... L... R...
- G72.2:
G72.2 P... X... Y... L...
Where:
P
is the subprogram number that defines the shape to be copied.X
andY
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.