The rotor will not stay parallel due to moisture and temp changes. The wider the sweep of your indicator the harder it will be to to tram the mill. I usually have a 6-8inch diameter sweep and do it right on the table. Just put .01-.015 thou on the indicator and spin it around slowly so the tip doesn't get broken, or worse. When loosening the 4 bolts to angle the head don't have them flip flop loose. You want just a slight amount of pressure. When tightening the 4 bolts back up watch the indicator for movement. This is how I do it and I get it within 0-.0005 TIR (total indicator reading). Also a good idea to mark the angle scales with a sharpie so when you have to do it again you can get close before adjusting. I also find it helpful to adjust Y axis when the quill is angled away and motor towards me. Practice this enough and you'll be able to do it in 5min or less. Kind of hard to explain this in writing.