New guitar nuts

BlueStrat

This is probably one of those things that everyone except me knows. 

How are nuts fitted to new guitars, whether fender, gibson, ibanez whoever. 

Are the fretboard slots cut by Cnc? And then when the nuts are fitted, are the string slots pre-cut by machine?
Or is the whole thing manual? Or partly manual?
The reason I ask is I was wondering why new guitars often need adjusting at the nut, or have tuning problems caused by a duff nut etc

WezV

Its not a duff nut or a factory flaw unless the slots are unevenly spaced, although the amount of extra height you get does vary a lot.

The final slotting is almost always done by hand.  

   They often leave them a bit high at the factory so they are playable out the box after they have shipped halfway round the world.... its much better to do that final step when the guitar has reached its new environment and had a week or two for the neck to settle.

Often the factories get it good enough, rather than ideal