I have used steel fabricated lathes in the past and have found that there is a harmonic that sets up when turning at certain speeds. It becomes a vibration that shows up in the final piece.
Paul, Interesting comment I have built a few all welded lathes and have not come up against this problem.
I don't doubt your experience just wondering what I am doing that causes me to avoid the problem.
🙂Now you've got me thinking will problem spend all week end trying to get the it to happen 😀