A few that I can't see have been mentioned that I know of:
Edge Precision
https://www.youtube.com/c/EdgePrecision (CNC, extremely informative, shows setups, the thought process of going about coming up with a machining strategy and figuring out what tooling is required, making custom tooling like custom profile cutters, machining intricate parts with deep holes, intersecting deep holes, etc)
Cutting Edge Engineering
https://www.youtube.com/c/CuttingEdgeEngineeringAustralia (shows the whole process of making a particular part using manual machines, and repair work to what is usually mining equipment. Also talks about tooling/machinery/equipment)
Allistairc132
https://www.youtube.com/user/allistairc123 (welding, air arc gouging, oxy-acetylene cutting, repairing large broken things, has recently put a lot of effort into producing some high quality longer videos such as
)
Fireball Tool
https://www.youtube.com/c/FireballTool (can't really sum this one up apart from being really interesting, the next video to be uploaded is always a pleasant surprise as to the subject matter, and something not covered before)
CNCFrezar
https://www.youtube.com/c/cncfrezar (mostly work on a large CNC gantry mill but shows other work)
Chris Maj
https://www.youtube.com/c/ChrisMaj (large CNC work, vertical turning too)
TheMetalRaymond
https://www.youtube.com/c/ELMETALRaymondMenendez (mostly work on a large manual horizontal boring machine)
JamesPark_85
https://www.youtube.com/channel/UC3mbksW8n2ipLL8_MhDSA8A (various machining, usually large, often titanium)
David Wilks
https://www.youtube.com/user/userwl2850 (lots of large manual lathe work, trepanning deep holes in shafts made of exotic materials such as inconel, although he hasn't posted anything in a while - hope he's OK)
That'll do for now