Piers makes some good points. As did a friend of mine I asked about this. He said:
"I think you’re underestimating the precision to which watch parts are manufactured. 3D printing doesn’t have anything like the requisite resolution and CNC milling would be fine for the plates, but the pinions and (probably) the wheels would need to be made on a gear hobber.
Not to say it wouldn’t be possible - there’s an Australian called Nicolas Hacko who is working on producing his own Australian-made movement and is documenting the process in considerable detail:
https://nicholashacko.com.au/manufacturing
As you observe even having the pieces in front of you, assembly will be another level of time and effort….
I’m interested as well to see Christian / WatchGuy has started fabricating parts as and when he needs them using a very inexpensive CNC setup:
https://watchguy.co.uk/cgi-bin/cnc
I’m not sure how close it is though - there’s a reason after all that Bremont / Chris Ward et al haven’t started making their own movements despite having plenty of cash to throw at the problem…"
Maybe not so easy after all . . . ..