at: http://rwb27.github.io/openflexure_microscope/docs/2a_basic_optics_module.html

Step 7: It is not clear which side of the lens should face inside the dark chamber.

Add TR-thread.

A good starting point (thread specs including tolerances) is here..

There is a bunch of CSG APIs out there and we need to catch up with it:
https://github.com/uetchy/jsxcad/blob/39d5a86072282ab06de4d150f0884dea414bba4d/src/jsxcad.js#L4-L9