I've slightly modified the drive cup and idler cup from thing:844167. I'm posting this in case it's useful to someone else.
I've made the following changes: the drive cup has been modified to fit exactly the shape of the stepper motor axis, and the inner diameter of the idler cup has been increased slightly.
drive_cup.stl and idler_cup.stl are the original files from jsc. My changes are parametric, you can check the OpenSCAD files or directly print *_modified.stl.