Bob La Londe writes:

Everybody says you need a
brake on the Z-axis if you use a ballscrew or it will backdrive.

That makes no sense. If you have a motor controlling the axis, then the
motor provides the braking. If you are running free (manual control with a
quill lever) then your hand or the spindle lock provides the braking.

Stepper motors are neither economical or appropriate for motion control
when significant force is required as is the case for CNC metalworking.
Servomotors are the proper element. Steppers' only virtue is relative
simplicity, but this is obviated by Geckodrive controllers and the like.