Hi,
The ER20 collet nut I have isn't balanced. In the first video you can notice the sound difference. Without the nut the spindle works smooth and quiet. When I put the nut on there is an increment on the sound level and some vibration.
In the second video you can see a simple vibration level test, using my smart phone.
You know there is an eccentric extractor ring inside the nut to hold the collet in. I suspect this is causing the imbalance.
So how to balance these nuts?