How to Mill a 360-Degree Circle With G-Codes
Mills operated by computer numerical control (CNC) can be programmed with G-code instructions to create arcs up to and including a 360-degree circle. You can mill a circle using the clockwise and counterclockwise circular interpolation commands. These commands cut lines in an arc, which you can combine to form a full circle of defined size and location. Doing so allows you to automate the cutting of circles when you produce designs.
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Instructions
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Add "G1 X- Y-" to your G-code program to position the tool at the coordinate where you will begin your circle. The dashes represent the X and Y coordinates that you will specify for the starting point of your circle. The G1 command goes straight to the specified location, which in this case lies in the XY plane.
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Subtract the distance in the X dimension between your starting point and the center of your circle to determine your I offset. Subtract the distance in the Y dimension between your starting point and the center of your circle to determine your J offset. Together, these relative offsets tell your controller how to shape the circle.
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Add "G2 X- Y- I- J-" to your program to move the tool in an arc. The arc ends at the point specified by the X and Y parameters, and it curves around the center specified by the relative offsets I and J, which run along the X and Y axes, respectively. For counterclockwise arcs, use G3 instead of G2.
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Repeat the steps to create arcs which extend to each quadrant of your circle. The quadrant boundaries where your circle has a horizontal or vertical tangent mark four points where the machine has to change directions. Some controllers can handle complete circles automatically.
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Simulate your G-code to verify that the program creates your desired circle. You can now mill a 360-degree circle with G-code.
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Tips & Warnings
Some controllers can use I and J as absolute instead of incremental offsets.
Some controllers allow you simply to specify the radius of a circle with an R parameter.
Machine controllers differ in how they interpret circle codes. Consult the manufacturer's manual before running your code.
References
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