I was just watching the "How it's made" show that featured brushes made on machines made by my friends at Carlson Tool. I have 14 of their machines all used for making wire scratch brushes but the same basic machines were shown making push brooms and scrub brushes. If you saw the show you can understand the process as the producers did a pretty good job explaining the basic operations.
John Carlson is the third generation owner and one of the most brilliant engineers I've ever known, and an avid fisherman. When he comes to town to visit I save all his cocktail napkin drawings as they are pure gold ideas. I've even had the privilege of having him steal a few of my ideas.