How would you draw this?

[old man emu]

Handily, there is an openscad design for a parametric ball pulley, specificallly designed for use with stepper motors, on thingiverse here: http://www.thingiverse.com/thing:12403

My experience using these is that accuracy suffers as the engineering tolerances on the ball chain are not that great. YMMV, but it's worth giving it a go.

I see your point about the accuracy of the ball chain. The chain that Mjolinor showed seems to be at the back end of the quality queue. The ball chain on my blind roller looks a lot better that that. Once again it's a case of paying peanuts.

Since you are both in the Old Dart, you should be able to cooperate easily on this project.

What got me with the Polargraph was the use of Polar geometry rather than Cartesian. If polar geometry allows you to work in 2D, could it be adapted to 3D? Would the adoption of polar geometry required the development of new CAD and CAM software to work with polar geometry?

Old Man Emu