Re: [CAD_CAM_EDM_DRO] ball screw vs lead crew

Terry Owens wrote:

>Hi,
>
>Ball-screws are important in the X and Y axis because they are designed for
>as near zero backlash as possible. Machine tools fitted with high precision
>ground ball-screws are also very accurate in the distance travelled. Due-to
>the weight of the Z axis the slide is always pressing down so backlash isn't
>a problem, except if you want to do a movement towards the tail-stock on a
>lathe.
>

This is not necessarily so. If you have the Z axis move the quill, the
weight
of the quill may be much less than the downfeed force on some cutting tools.
So, the tool may hold it up against the upper backlash limit during some
operations. This may or may not be a problem, you really have to
evaluate it
for each situation. Some knees are tight enough they won't always drop as
the screw is relaxed, and they need the screw to pull down on them.
Then they
drop with a thump.

Jon