Arc and Circle I and J code calculator for GCode cutting paths

I & J Arc Code Calculator (with updated spreadsheet)

I had a need to hard code a circular PCB cut out CNC code that would cut four arcs around a milled PCB and leave four breakout tabs to retain the board in place in the blank until the job was finished.

To create I & J codes you need to know the start point, end point and radius of the arc.   The end point becomes the X and Y.  The  delta X and Y location relative to the radius centre point X and Y becomes the I and J values.   You can also add a depth of cut value for Z as part of the block.  Note that the Arc is assumed to run anticlockwise when using a G3 code running from start point to finish point.   Use G2 if you want a clockwise motion.   The principle is the same with both rotations.

You end up with a block code of the format G3 (G2) Xa Yb Zc Id Je where a,b,c,d,e are the coordinate values.  I found that working with positive and negative values when trying to find the I and J values relative to the centre was hurting my brain.   A spreadsheet was needed …..

Screen shot of I and J calculator spreadsheet
Screen shot of I and J calculator spreadsheet for G2 and G3 coding with examples based on CW and ACW arcs around quarters of a circle with small gaps between each arc.


You can download the sheet as a ZIP file from the link below.

Arc and Circle Calculation Sheet for GCode

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