Quote Originally Posted by D.C. View Post
Putting the centre at the same height as the bed results in the shortest required z-axis.
No it doesn't it puts it at the longest Z extension. It will only be shortest when cutting at the outer radius and ever millimetre towards the centre the extension gets longer weaker and therefore the chatter will get worse.
I know what your saying but really it's down to the size of radius you want to cut or the size your most likely to do often. Why would you want the centre 7" away when your mostly turning 2" stock.? You wouldn't set your rest 7" away from centre on a Manual lathe if you where turning 2" stock so why would you in this case.? . . .That would just be creating a weaker machine for the Odd occasion when you want to turn larger diameter.!

The ideal would be an adjustable position and that's what I'd probably do in reality.! . . BUT.!!. . . . Like I said it's only a mock up and if you wanted 6" from the floor then go for it. But this was drawn just to show the principle with simple Leg or spindle turning in mind so that's why it landed there. . . Oh and it's 4.5" away there so thats 9" Diameter which is more than enough for most 4th axis work.!!