I have recently been battling with some bad mid range resonance on my x3 mill. I am using a Xylotex 4 axis drive with 425 oz steppers. I had reduced the resonance by greatly reducing the Vref on the drive. However this is a very poor fix as it hurts performance. I looked at several damper designs used on engines. Elastomer, fluid and a pendulum type. I decided a pendulum type might offer the quickest response and be able to absorb a wider frequency range so I gave it a shot. The results are nothing short of amazing. It completely absorbs all resonance and vibration problems I was having. I was able to turn up the Vref to full power without a trace of resonance with the damper installed. Remove it and the ugly resonance is back. It's dramatic how well this damper works. TCI makes a automotive type of this damper for racing and they call it the "rattler". This is because when it is working you can hear the rollers working. It's very interesting to hear this damper work. At feeds where there was usually resonance the damper will be very active with the rollers making noise while they are absorbing the resonance. At speeds when the stepper is in a resonance free operating range it is dead silent. It's easy to make. My design is about 2.45 in diameter with 9 rollers.The rollers have .045 clearance in the pockets. http://i109.photobucket.com/albums/n...rdamper001.jpg http://i109.photobucket.com/albums/n...rdamper002.jpg http://i109.photobucket.com/albums/n...rdamper003.jpg http://i109.photobucket.com/albums/n...rdamper004.jpg Steve