Nautilus gears with involute herringbone gearing - customizable

! be sure to have downloaded the newest version!

this project continues my previous project (http://www.thingiverse.com/thing:769012) which I published with an open callenge in mind. As it transfers the method I used there from 2D to 3D, I thought I'd besser set up the solution as a separate project.

With ordinary fixed pitch gears, herringbone gearing is easily achieved by applying the powerful OpenSCAD primitive 'linear_extrude' with a 'twist' argument to a 2D object. When it comes