wrote: (clip) although half of the bottom pulley moved
left and right, the moveabvle (?) top pulley with the spring never moved
(clip)
^^^^^^^^^^^^^^^^^^
Without knowing more about your lathe, I am just guessing, but what you
describe sounds like classic Reeves drive behavior. The sliding pulley-half
gets dirty, and the spring is not strong enough to close it and keep the
belt tight. The answer is to clean it up--force it to more a little--spray
it with WD-40. If you can, disassemble it and clean it well. Then lube it
with a little wax (preferably.)

In the future, clean it before it gets stuck--it will be a lot easier.