3 phase milling machine to single phase.

[MarcDant]

I have a teco westing house ac inverter 230/460 volt 3 phase .50-30 HP. Its worked well for over 10 years now and still works well. You cant tap threads into holes because it takes 5 seconds or so to spool to 60 hertzs .May have better inverters on the market now.

[1967 4K]

There’s also an old school device called a Roto Phase thats been around for decades. The most cost effective way to go and simple to install.
Talk to an electrician that’s worked in motor control and he’ll tell you how to make a converter out of an old three phase motor the same size as your mills motor. Cheapest of cheap.