There are many descriptions and movies showing how to balance a propeller but I haven't found any clue on how to balance motor and attached shaft. I bought 4 EMP motors and it's extremely hard to attach the shaft to maintain the axis. Take a look on attached screenshot to see what I'm talking about. This creates pretty strong vibrations even if the and of shaft round a circle less than 1mm diameter.
Screws attaching this shaft were tighten well. Is it normal? Or is it because motors are "cheapo"?
It was mounted on some wood just for testing. It doesn't change anything here.
I have 4 such motors and 3 of them have this issue. I was not able to mount shafts perfectly straight. Hence the question is there a way to fix it other than just buying different motors.
You could take some very fine sand paper, like 400, and hold it on one side while its rotating to remove some material until it is in balance. As long as you don't ding the threads they should continue to be useable.