hy bob, i don't have time to read all, but all i can tell is that many shops consider buying another new/used machine, without considering 1st the possibility to increase productivity with less cost compared to the new machine
... if you are working in 1 shift, go 2 shifts
... if your tools are neah, try better tooling
... when the spindle is stopped, what is the cause ? make a list with all the causes and their duration; after few months you should now exactly how much time was lost and why; it seem to be a mill; common causes that leads to mill downtime are :
...... less preparatory operations, downtime with setup, etc : invest in diy fixtures, quick-change types, etc
...... too much time to edit and reload the program
...... chips evacuation
...... restart issues during long operations
... when the spindle is spinning, what is the productivity ? like is it possible to do this job in 50%-75% of actual time ?
if you wish, considers the improvement costs, and compare them to the monthly costs and long term costs of getting another machine
a cnc has to be considered a cost unit, and there are cases when a new machine is decreasing the profits, even if it is running / kindly