Cliff, this is just my opinion but unless you are planning 24/7 operation of the lathe i.e. production manufacturing an inverter rated motor is not necessary. Just use a quality made motor. and if it is a used one inspect it carefully for damaged insulation, possible bearing problems and overall condition. One of the biggest complaints with running a VFD is a high pitched noise coming from the motor. This can usually be eliminated or at least reduced by adjusting the carrier frequency or it can be ignored. (the noise is simular to that of running a variable speed hand drill or mini mill at very very slow speed) Most inverters are well protected internally in the event of motor failure (shorts) so the chance of inverter failure is minimal. As for insulation ratings, most modern motors have a minimum 3:1 factor but the listed rating will be lower. If not posted on the spec. plate you can go to the manufacturers charts and get further info not listed.
Wiring is pretty straight forward and simple for a basic install. The difficult part is when you want to have features already installed on the machine intergrated with the VFD control. There are usually some controls on the machine which will require wiring changes and will be operating at a different voltage than originally designed. Some carefull planning and drawing up a diagram is recomended.
Darren M.
http://groups.yahoo.com/group/gingery_machines/app/peoplemap/view/map
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