G-Code Example Program - CNC Machines 360

Learning G-code is much easier when you can see it in action. This example program will walk you through a simple G-code script that moves a CNC tool to cut a square. Along the way, we’ll explain each command so you can understand how it all works.

Objective

Create a square with sides of 50 mm, starting at the origin (0, 0), using a CNC machine. The tool will move to the starting position, cut the square, and then return to the home position.

Example G-Code Program

Here’s the complete program:

G21           ; Set units to millimeters
G90           ; Use absolute positioning
G17           ; Select XY plane for cutting
G00 X0 Y0 Z5  ; Rapid move to the starting position above the material
M03 S1000     ; Start spindle clockwise at 1000 RPM
G01 Z-1 F100  ; Lower the tool into the material
G01 X50 Y0    ; Cut to the first corner of the square
G01 X50 Y50   ; Cut to the second corner
G01 X0 Y50    ; Cut to the third corner
G01 X0 Y0     ; Return to the starting point
M05           ; Stop the spindle
G00 Z5        ; Raise the tool above the material
G28           ; Return to the home position
M30           ; End program

Step-by-Step Explanation

1. Setup Commands

G21: Sets the units to millimeters. If your machine uses inches, replace this with G20.
G90: Enables absolute positioning, meaning all coordinates are measured from the origin (0, 0).
G17: Selects the XY plane for cutting operations.

2. Move to the Starting Position

G00 X0 Y0 Z5: Moves the tool rapidly to X=0, Y=0, and Z=5. The tool is positioned above the material, ready to start cutting.

3. Start the Spindle

M03 S1000: Starts the spindle spinning clockwise at 1000 RPM. Adjust the speed (S1000) depending on your material and tool.

4. Lower the Tool

G01 Z-1 F100: Lowers the tool to a depth of -1 mm (cutting depth) at a feed rate of 100 mm/min. The tool is now ready to cut.

5. Cut the Square

G01 X50 Y0: Moves the tool in a straight line to X=50, Y=0, cutting the first side of the square.
G01 X50 Y50: Moves to X=50, Y=50, cutting the second side.
G01 X0 Y50: Moves to X=0, Y=50, cutting the third side.
G01 X0 Y0: Returns to X=0, Y=0, completing the square.

6. End the Program

M05: Stops the spindle.
G00 Z5: Raises the tool to a safe height above the material.
G28: Sends the tool back to the home position.
M30: Marks the end of the program.

Customizing the Program

You can modify this program for different shapes or dimensions:

Change the Size: Adjust the X and Y coordinates to create rectangles or other shapes.
Depth of Cut: Modify the Z value to increase or decrease the cutting depth.
Feed Rate and Spindle Speed: Adjust F (feed rate) and S (spindle speed) to suit different materials or tools.

360 Key Takeaways

G-code programs are made up of commands like G00 (rapid movement) and G01 (cutting movement).
Always include setup commands like G21 (units) and G90 (positioning) at the start of your program.
Testing with simple shapes like squares helps you understand tool movements and program flow.
Use comments (e.g., ;) to annotate your code and make it easier to read.

Conclusion

Writing G-code programs is a valuable skill for CNC operators, and starting with simple examples like this square-cutting program is a great way to learn. Practice tweaking the parameters, and you’ll quickly gain confidence in creating your own programs. Happy machining!