Curing “Crop Circles” with Mach3 and Inkscape

Nooo, crop circles!

In a previous article, I wrote all about my ingenious method (or so I thought) of straightening lines so that Inkscape and Mach3 would play nicely together.  Although this method works fairly well, there is a much simpler way to make Mach3 interpret everything correctly.

After a brief email conversation with Mach3, the suggestion was made that I might be in the wrong “IJ mode”.  They were definitely right, and after the change the crop circles magically disappeared!  You can change the default mode (as I did) on Mach3 under Config>General config.

Alternatively, the gcode file can actually specify what IJ mode is to be used (G90.1 or G91.1), however, I have not tried this yet.  One just has to write, literally, “G90.1” or “G91.1” towards the beginning of their code to set the mode.  See this conversation in CNC zone.

This whole thing has to do with whether the IJ coordinates – the center point of any circle drawn – should be absolute (G90.1) or incremental (G91.1).  I still have a lot to learn, but the coordinates are the theoretical center of any circle (or partial circle) milled with Gcode.

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So, as with many things like this, it pays to check the simple things, or ask for help before you start devising your own crazy method.  That being said, I think I’ve learned a lot about Inkscape and am starting to get more familiar with Mach3 during the process, so it wasn’t a total waste.  They both seem like very good programs so far.


  1. This was very very helpful. I thought my code was wrong. Changing to incremental got rid of those crop circles.

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