I have double shaft steppers. They mount on the back.

Me too but how you attach the damper to the shaft, with a coupling?
Nicolas

It's got a hub that get's glued into it, and has a setscrew.

Read through this.

http://www.cnczone.com/forums/showthread.php?p=256639#post256639

Here's some pics of the dampers and a YouTube video showing with and without.
http://www.youtube.com/watch?v=UJjivsVwSsQ

Nice work Gerry, thanks for sharing
Nicolas

Well Gerry my dampers are a shame in comparison to yours but I did notice a reasonable decrease of resonance on the Y axis. The damper is press fitted to the motor shaft and as the time goes I may get some better ideas but for now it will do.

The diameter of the disks is 2-3/8" and that is the max I can fit there considering the available space. The Y axis motor is under the table and I have very limited space to work on the shaft without major modifications.
Nicolas

This design I got it from the web sometime ago (solsylva?) and after the installation resonance=0. Very happy about it

Did not notice any speed increase in the Y axis but at least she now works smooth and silent, coffee grinder sound is gone

The caster wobbles a bit, very difficult to do a good align job, but makes no difference.

Later I might get a proper coupling and then there will be no wobbling.
Nicolas