I make spindles from stainless shaft material that is already ground to a fine finish.
It is important that this part screws all the way into the Rear End Plate. There is a thread relief counterbore in the plate, but the spindle male thread must run as near to the shoulder as possible. I have an 8-32 hex repair die that has a tapered opening on just one side. After cutting the thread with a round die (which is tapered), I run on the repair die with its untapered face leading.
This drawing also shows the oversize screw that secures the spool. Alloy c792 is a highly machineable 12% nickle silver. Its male thread needs the same treatment as the spindle. I have been making the “spherical” radius by cutting a couple of cone surfaces and then working over with a file. The slot is just wide enough to accomodate a newly minted U.S. quarter.