They are just not making them right. First you need to turn up a thick piece to a dummy spindle the same thread diameter and pitch as the wood lathe . Then weld the nut to the plate as close to a centre hole as possible . Then spin it onto the dummy spindle still held in the chuck backwards and turn the face of the nut flat. Then turn it around and spin it on and lock up the turned face of the nut against a shoulder on the dummy spindle . Then machine the plate true on as many surfaces as you can get to. After that it should run true to a spindle thread and be reasonably balanced.