Sensor less vector vs closed loop vector

[Clive S]

I'm looking for a VFD for a cnc lathe conversion

Have you decided what you are going to control it with ie MAch3 Linuxcnc etc.
I have done a lathe conversion Myford S 7 using LinuxCnc with a 64 slot encoder on the spindle using (A + B + index) that controls the Z in time with the spindle you can even rotate the chuck by hand and thread.