Example OpenSCAD Screw Thread Transformation

thingiverse

Inspired by speedymollusc's Openscad Screw Threads, this example function transforms a radial polygon representation into an axial polygon suitable for linear_extrude with rotation. The radial representation is a list of coordinates [[ r1, z1 ], [ r2, z2 ], ... ] where each pair contains a radius and a z position. This polygon generates a thread-like shape when used with rotate_extrude, but unfortunately OpenSCAD doesn't allow rotate_extrude with advance to produce screw threads this way. If a screw were cut perpendicular to the axial direction, the cross-section would contain thread information in a different form. I'm calling this the axial polygon. This polygon generates the thread shape when used with linear_extrude and twist. A pair of functions contained within a short .scad file transforms a radial polygon into an axial one, suitable for linear_extrude with twist. This is similar to speedymollusc's work but solves it in a different way. This is intended for OpenSCAD experts who need to support a screw thread library.