[Kazsaw]

How frequently should backlash need to be adjusted on a vertical milling center (i.e. VF-3SS)?

[Al_The_Man]

As required
It should normally not have to be adjusted on a regular basis, it could be checked once a year say, during a maintenance period or if & when any kind of positioning error exists.
I assume you are refering to back lash correction by parameter? As ballscrew etc should be pre-loaded and do not generally have back-lash adjustment.
Al.

[Kazsaw]

Yes..by parameter. If we find this needs to be adjusted more frequently, do you know if that signifies a particular type of problem?

[Al_The_Man]

On a ballscrew system I would not consider frequent adjustment normal it would pay to check lubrication and/or end thrust bearings require adjustment or attention.
With proper lubrication ballscrew wear should not show up until many 1000s hrs run time.
Al.