However, what you could do, is attach a reasonably sized motor to the static converter, and you have a rotary converter.
I have just spoken to a very helpful guy at Transwave and he has suggested the same thing, Not ideal but would get me running hopefully.

More advanced static converters let you switch capacitors in/out to try and compensate, and some even do it automatically for you.
Yes this one has a switch for the capacitors so I can load up the dummy motor and get it reading right before I power up the lathe, Just have to hope I can get a bigg enough dummy motor to smooth out the voltage.

Its not ideal but at least i might be able to use the lathe and make sure it will do what I need it to do before spending any more money on a digital converter or a retrofit.