"Bob La Londe" fired this volley in
:

There is also something to the way resources are allocated for USB as
opposed to a dedicated hardware communication port. I'll leave that


I should have added this -- the way more sophisticated CNC machines that
run off windows work is that they have an external "controller". Windows
sends the commands it needs done as it can get around to it. The
controller 'assembles' the required data and control information, and
only sends it to the hardware when it has everything necessary to do the
commanded motions.

IE... the MachMotion guys, who sell very nice 'kit' solutions for CNC
conversion, won't guarantee that their lathe package can do threading
unless you use their external controller. Some folks get away with it -
at very slow speeds - some don't at any speed.

LLoyd