I took John McNamara's advice and watched Marc L'ecuyer's videos and they are, indeed, excellent. Everything John described.
In the ones I saw Mr L'ecuyer describes at some length setting the head on a column type 'mill' then trying not to move it again. I have a Warco Economy machine with which I'm very pleased and use a lot. As members will know, this is a round column design (not like a Bridgeport with a 'knee' where you raise and lower the table) and I wind the head up and down fairly frequently to accommodate different tools and jobs.
What I'm now wondering is whether this is bad practice.
Mr L'ecuyer tells us to use the 'long tool method'. That is, fit your longest tool to the quill as accurately as you can – in my case that would probably be a collet arbor and about a 20mm end mill – tighten the head with it in position then leave it alone and only use the quill thereafter.
Makes sense?
However, I guess if you don't adhere to what Mr L'ecuyer advises you might swing the head around the column to some extent to access some jobs. But if you do follow his rule couldn't you normally reach the work by winding the table on the X or Y axis or both?
Martyn