I designed and printed this harmonic damper to see whether it could kill some of the awful noise my printer has been making since I converted the Y-axis to screw drive.  The short answer is, no it didn't help.  You can see a lot of videos on Youtube by guys testing these things on their CNC mills, but all the tests are run at high speed and typically in forward or reverse, not at low speeds, with a lot of stopping, starting, and reversing direction like a 3D printer does (and a CNC mill when it's actually cutting).My test video here: https://vimeo.com/118775688 and here:https://vimeo.com/118775689If you're going to try it, print solid or with maybe 50% fill, no brim, no support material necessary.  Glue the pennies together in stacks of 5, then put them in their holes in the disk.  Screw the cover down with 6-32 screws and push the thing onto the flatted 1/4" shaft of your dual shaft NEMA-23 motor.