Thanks for your insight. At the moment I don't see any of these points being an issue, but who knows the future.

My reason for the multiturn pot is to get more control over speed. The 3/4 turn pot makes it difficult to set a speed.

My lathe has a very effective foot brake.

- Yes, using a 10 turn pot with counting dial, you can easily set the VFD frequency to an accuracy of +/- 0.01Hz. But that does not mean that the actual motor shaft rpm is that accurate. An induction motor does always have some slip, and this slip can easily be in the magnitude of more than 10% as the motor is loaded. What point is there in you setting VFD frequency to say accurately 50.17Hz, if the motor rpm does drop by 200rpm and more just as it is loaded? This slip is, by the way, much greater with a simple V/Hz VFD as it is with a sensorless Vector VFD that compensates somewhat for slip.
You are being too pedantic here. So what if the motor slows down. It will anyway. I am not trying to get exact speed. If I left the VFD at a set speed (50Hz) and just used the gearbox it would be no different.

Remember the large mechanical variator handwheel found for variable speed selection on older lathes before the advent of electronic speed control? From a point of user-friendliness, I feel that using a 10 turn pot on a VFD is very much like going back to those days.
I can see your point, but I am not trying to get on the fly speed changes. Time will tell whether this is worth the effort. Swapping back to a 3/4 turn will only take a few minutes.

Dean