I have only seen those 3 jaw chucks with a collet attached to the back, not threaded like yours. The threaded piece that the chuck screws into has got to be like a collet, looking at the pictures I would think if it is not coming undone easily it might have had some form of glue used to help hold the drawbar onto the collet. You probably already know this but it needs to come apart where I have stuck the red arrow, once you get the draw bar undone, this is where it should seperate( I am guessing?).Have you tried a gentle heat on it to see if it comes loose?
David is the forums lathe expert, he should be able to help now we have some pictures.
Good luck and keep us posted, looks like a good lathe!
Paul.
