last update 2020-01-26

• uses new features of OpenSCAD 2019 and renders much faster
• help(), help_gears() echos module prototypes and parameter defaults
• fixed: helix angle is now height independent
• added torsen differential as programming example

Background

With this ongoing project I want to present an unusual approach for gear calculation in library form. It is meant for scholars, students and tinkerers, who have started to program with OpenSCAD. Offering many useful, well defaulted parameters, it also addresses most of the needs of professional and semi-professional programmers, who will not only find a large scope of functionality, but also an inspiring self explaining library design.

Usual code for drawing gears uses the involute function in a constructive way. There are some nice projects in this forum showing that path. It was also my first approach some years ago. But somehow I never really found out how to do proper profile shifting within that approach. And it seems to me, others also didn't. OK, there is not much explicit code published about gears and also math is not everybody’s darling.

To do the really nasty tricks with gears it is essential to have profile shifting. So my idea was to use a cycling tool and cut gears out from a circle, just the way they are crafted in industry.
Easy principle, easy and amazingly powerful solution. Its 'subtractiveness' also nicely fits to the declarative paradigm of OpenSCAD.