I can't be sure from the drawing either but either way the top has to come off. It depends where the lock engages the shaft. Put a piece of wood over the end of the shaft or nut minus collet and tap on the wood to drive the armature out of the bearing. When it lets go it's going to fall so be prepared have something or someone catch it.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.