Computer Numerical Control (CNC) milling machines are sophisticated pieces of equipment that can create intricate parts with high precision. A crucial aspect of operating these machines is understanding the programming language that controls their movements. In this article, we’ll explore the G03, G90, and G91 commands, which are fundamental to creating circular paths and setting position modes in CNC milling.
Usage Format
- G03: Circular interpolation, counter-clockwise (CCW)
- G90: Absolute positioning mode
- G91: Incremental positioning mode
Explanation
G03 is used when you want the milling cutter to move in a counter-clockwise circular path. The command requires additional parameters such as the radius of the circle or the endpoint of the arc.
G90 sets the machine to read from a fixed, known point on the workpiece. All coordinates are given as distances from this origin point.
G91 switches the machine to incremental mode, where each move is relative to the current cutter position. This is useful for repeating a series of operations at different locations on the workpiece.
Example
Let’s consider a simple program that uses these commands to mill a circular pocket:
N10 G90 G17 G20 (Set to absolute mode, XY plane, inch mode)
N20 G00 X0 Y0 (Rapid move to start point)
N30 G01 Z-0.5 F15 (Linear move to depth of -0.5 inches with feed rate of 15)
N40 G03 X1 Y1 I0 J0.5 F20 (CCW arc to endpoint X1 Y1 with a center offset I0 J0.5)
N50 G00 Z1 (Rapid move to safe height)
N60 G91 (Switch to incremental mode)
N70 G28 G91 Z0 (Return to home position)
Here’s a text diagram to illustrate the G03 command in the program:
(Start)
|
| (I0,J0.5)
| .
v / \
X0,Y0 <--- X1,Y1 (End)
In this example, the cutter starts at X0 Y0, moves down to a depth of -0.5 inches, then performs a counter-clockwise arc to the point X1 Y1 with a radius defined by the center offset I0 J0.5. After completing the arc, the cutter returns to a safe height before the machine switches to incremental mode and returns to the home position.