Other Tutorials:

Ashomsky (video)

     The Factory is a simple but impressive trick that uses one arm to carry a ball over the entire pattern and drop it as if on an assembly line (hence the name). The trick is best performed with rigid, robotic arm movements, and is in fact also known as the Robot. The unusual motion of the Factory makes it crowd favorite, particularly among younger audiences.

    To learn the trick, it's useful to think of it first as a modified Fake Columns, with a "fake" that travels over the pattern. 
    Practice this arm motion until you can execute it smoothly without interrupting the balls being thrown. Next we are going to add in the actual drop and catch. Start with a basic Fake Columns, and then start to do the pattern above, except this time you are going to release the ball once your hand reaches the other side, and then claw catch the center ball.
    This is going to probably be the most difficult  stage of learning the Factory, since the coordination of your arm movements and your throws will likely lead to mix ups. Once you can do one cycle of the factory smoothly and consistently, you can start chaining them together to get the full Factory.