These gripping gears mesh with and rotate around each other, but with no axles and no frame.
This version has "pass-through" holes, that allow a solid object (e.g. a screwdriver) to pass between the gears.
YouTube video: https://youtu.be/RBZG8M8_a8Y
To make these, you will need to print four copies of each of the files. Two of each file are bolted together using standard M3 nuts and bolts to make each gear.
This is joint work with Sabetta Matsumoto and Will Segerman. Thanks to ICERM (https://icerm.brown.edu) for their hospitality during some of my development of this design.