To add to what Rodger said, if you imagine that you had 100K cash money today, option 1 you buy a cnc and ancillary equipment, market, sell work, build, etc... OR you take that 100k and invest it...
At 8% annual compound, in 15 years your earn $217,000.00. So over the life of the 100k investment in the cnc youd hope to come out with that as a bare minimum (a net break even).
Making 15K a year cash in the bank from the cnc sounds easy but it needs to be 15k clear after you've paid yourself. Because youd have made the 217k sitting on your duff with the money in the bank lol.