Making progress at: https://github.com/WillAdams/gcodepreview in case anyone is curious, but this getting close to being done raises my next project which I believe will need for me to know more about conic sections. Suggestions on a book on conic sections which would approach this in a fashion suited to a person who does not have a great grounding in math (I'm reading through the _Make: Geometry/Calculus/Trigonometry_ books) which goes beyond the coverage of conic sections in that Trigonometry book in a fashion which is applicable to OpenSCAD? William -- https://designinto3d.com/ Sphinx of black quartz, judge my vow.