Yes, I know the VFD part, it better be stable then. But... I'm amazed! The threads looks awesome and not even a single feedback from the spindle!
When it comes to lathes I can only compare to production machines and EMC. Maybe it's possible to run EMC without feedback too, but the guys that runs it for threading uses at least one click per rev as far as I know.
I see one problem with the no-feedback version, what happens if you want a thread to start exactly on a specific place? But on the other hand, even if I have been producing stuff with that requirement - how often will that happen?

Still amazed,
Sven
Actually it's not that close. If the VFD says its 1000 RPM, you are probably running under by up to 10%, depending on the torque. The less torque, the closer it runs to the actual freq. Some drives have a setting to compensate for this.

Eric