This page was written by me, for me. Running this code on your own CNC will destroy your machine, shave your cat, and possibly cause a dimensional portal to appear. I take no responsibility for any of it.
This generates code to make a flat surface. Enter the X+Y dimensions, the depth, and the step over amount. All values assumed to be in mm (because my machine is in mm, and as I said, this is only for me). You should specify a larger size than your workpiece, because a) we want the Y moves to be done outside of the workpiece, and b) rounding will result in a slightly smaller area than the specified X/Y values.