Knee for z-axis control?

Hi all,

I will be retrofitting my Bridgeport mill soon and know that some
have used the knee for z-axis control. Does anyone here have any
experience with this method? If so, what should I take into
consideration if I decide to go this route? The mill has a 9" X 48"
bed.

Is a counterweight to offset some of the lifting load preferable?
Did you use the original acme screw/nut, or retro with a ballscrew?
What would be a reasonably sufficient drive in terms of motor torque
and gear reduction?
What are the pros & cons of using the knee opposed to the quill?


Thanks, Eric