Hello ZeljkoM, I am a newbie,(joined today),and am interested in your query. Have you measured the radial run-out? I have a RF-45 clone and twice when changing head height have been interrupted and when I returned usually a day or two later have resumed where I left off but have forgotten to check that head was locked in Z-axis and wondered at cutting/finish problems so now have the habit of triple checking everything and if I move head immediately lock it again. I mention this as you stated the you do not use the quill but only the Z-axis so I would like to know what you have done to remove any play on the dovetail? About the only thing I can think of would be many hours fettling with a scraper.