I would not construct a PMA with obvious eddy problems.
I expect you did not drop a neo down a copper pipe. (Aluminum would work too)
I just did it for you. And my wife wonders what I do on days like this.
Unknown grade HD neo, certainly N35 at most. Slightly under 1/2" x slightly under 5/8" x 3/16".
Brand new thin-wall 1/2" copper pipe 10' long.
The magnet fits loose in the pipe. There is no corrosion on either part.
At about a 45 degree angle it took 19.5 seconds to fall through.
As close to verticle as I could guess took 9.5 seconds to fall through.
Only PMA eddy experience in induction motor conversions. They are laminated and have some iron losses, partly due to eddy currents. It can be felt as a difference in how hard it turns with magnets compared to before the magnets were added. Dinges Peter did some in depth testing of iron losses in a small conversion you may find interesting. There is nothing I can do about it in a conversion, so I don't worry about it.
If you are not having a noticable problem with eddy currents in the rear disk, I expect the lathe is too powerful to notice it being dragged down, or the air gap is far too large (if the air gap is too large, the coils are too thick and much of the copper is just adding resistance).
A dual rotor has no real iron losses and that's why they spin up so easy.
A single rotor with laminations, or a conversion, has iron losses. And that's why they "drag" even before there is a load.
A solid, non rotating disk will hold the PMA back like a dragging brake.
Ed's page shows a LOT of PMAs with laminated cores. I doubt he ever cut a corner because of a lack of proper material on hand.
The eddy currents get worse with speed.
Do not underestimate the effect. It stops trains and roller coasters. It may be in use as a fail safe elevator brake. Maybe google "magnetic brake".
G-