Here is how I remove the tapered shaft of the ball joint. The taper causes
the shaft to grip even after the nut is removed.A balljoint fork may tear
the rubber boot.That is ok if you dont need to reuse the ball joint.

Loosen the big nut a few turns. Then, using a 2 pound hand sledge hammer,
hit the cast iorn wher the shaft goes throught the cast iorn. Vibrations
wil cause the shaft to release itw grip.Then finish removing  the nut.