Re: Z axis on the knee, how practical????

I've used both knee driven and quill, Servo's retrofit is knee
driven, quite fast and uses an Acme screw, you have to remember if
there is no assist on the knee then the weight keeps the backlash in
one direction. Now a friend of mine did a retro with 1100oz steppers,
and couldn't get the knee to move very well, not enough guts in the
stepper, so he put air assist on it. One thing to keep in mind, that
with knee motion you still have the quill where you can use manually
at the same time. For my machine I have a Hurco KM3 machine, it's
quill driven, it's not bad but for what I do I miss not having the
manual quill. The ultimate I think is a bed mill with the Brdgeport
style head, here you have the whole head going up and down and manual
quill. It's on the wish list of things to buy.
Richard Konnen