This thing is an printable spider coupling designed for a rubber insert. It has robust clamping, and should be well balanced if tightened evenly.
If the rubber spider is cut cut correctly, there will be axial compression cushioning, angular cushioning, and rotary cushioning without slop.
This design must be kept in compression, it will not stay together under tension.
Video showing low-speed operation, with an exaggerated angle:
Video showing higher speed operation:
(Alternative experimental version here that uses silicone sealer: http://www.thingiverse.com/thing:7831 )
This is an original work, but owes inspiration or is similar to these things:
Universal Joint by twotimes:
Flexible shaft coupling by twotimes:
Prusa Mendel PLA Coupling by Griffin_Nicoll
Printed flexible beam coupling by jmgiacalone
Spider coupling - 5mm axis to M8 drivescrew by lievenstandaert:
Hoeken's Coupling by hoeken:
Print the parts. Use a solid profile for strength. Clean up. Run a 3mm drill through the clamping holes.
The clamps will have good clamping force, but limited travel. The part should press onto the shafts with some reasonable force. If they are loose on the shafts, please make the shaft hole sizes slightly smaller and re-print.
Take the printed spider, and use it as a pattern to cut a spider out of rubber. The thickness (Z) of the rubber is pretty important. Too thin and the coupler halves will touch. Too thick and it will get wobbly. The shape is also critical as far as symmetry. If it is not symmetrical, the shafts will wobble. The absolute size if the X & Y can be a little large, it will just "pre-load" the coupler a bit, and assure no lash.
A softer rubber (perhaps cut from a sheet of neoprene wet suit material) will give more cushioning. A harder rubber will make a stiffer coupling. I have considered using a slice from a rubber eraser. Maybe slice up a rubber bumper?
If you build this, please feed back what you use and how it works for you -- thanks!