The brass knobs arrived from Lee Valley Tools and look beautiful. This is what I hoped the spool covers would look like when the disks I turned on the lathe were fitted with the knobs:
Unfortunately the base of each knob is not thick enough to be drilled through safely with a 1/4" HSS drill bit needed to fit the spool spindles of the typewriter:
Plan B involves using 9/32" brass tubing and a brass washer to make a new base for each knob, and cutting the top off the knob and fitting it to the top of the tubing, so I'll see how that goes.
Part 1 Part 2 Part 4