What is CNC machining: https://youtu.be/FNYEXjRmDtI
CNC Learning Academy: https://academy.titansofcnc.com/
Techniques to make a hole: https://www.custompartnet.com/wu/hole-making
https://en.wikipedia.org/wiki/Turning
https://www.custompartnet.com/wu/turning
https://en.wikipedia.org/wiki/Milling_(machining)
https://www.custompartnet.com/wu/milling
Milling Crash Course (each 3 minutes)
https://en.wikipedia.org/wiki/Electrical_discharge_machining
How does erosion work (1min): https://youtu.be/L1D5DLWWMp8
Wire EDM (3min) https://youtu.be/pBueWfzb7P0