VFD to run 7.5 hp, 2 speed 3 phase motor on single phase.

Sorry for the newb question. I'm looking to get a lathe up and running.
I've done a fair amount of research,but want to make sure its done right the first try.
I know that the VFD needs to be oversized and was planning on using one 15hp rated.
What I'm not sure on is if I should wire the VFD directly to the motor's high speed input and use it for all controls.
Or to wire the vfd in place of the contactor, and keep the existing lathe switch. I have read both ways being used, and that you have to be careful to never switch speeds with the motor turning.

Any suggestions?

Since it is a constant torque motor, I would run it on the high speed setting. With a VFD you will get ~the same performance lowering the speed with the VFD. I have had a few issues trying to use 2 speed motors with VFDs, sometimes they work and sometimes they just won't run smoothly, despite tweaking the parameters and auto-tune. If it is an older motor, you might think about using a newer 5Hp single speed motor if you can find one that is inexpensive and going with the next size down VFD. There are also some single phase input 5Hp VFDs that work well. Otherwise you would need a 15Hp 3 phase input VFD, and check that the particular model works with single phase and the derating (something like the WJ200-110LF). You will need a braking resistor, and wire in a free run command when using a mechanical foot brake. Your input service needs to be 125% of the VFD input current, not the motor, so all that needs to be factored into the cost.

Have you given thought to using an RPC if you need 3 phase, would be more cost effective and simpler if you do not need the VFD features.

started off looking at building a rpc, and looking for a 15hp motor to make one with.. I haven't had much luck finding anything local so far. Over the weekend I asked my brother in law if he had one laying around at his work. He said he would look, but there is a better chance of him finding a used VFD, so researching if it would even work lead me posting above. I built a rpc for my bridgport but with only a 3hp motor..

AC krom said:

started off looking at building a rpc, and looking for a 15hp motor to make one with.. I haven't had much luck finding anything local so far. Over the weekend I asked my brother in law if he had one laying around at his work. He said he would look, but there is a better chance of him finding a used VFD, so researching if it would even work lead me posting above. I built a rpc for my bridgport but with only a 3hp motor..

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Don't mess with the two speed motor, just wire it for high speed.

Use the lathe controls and contactors to trigger the VFD low voltage control and logic.

Anything less is a waste of time.