Make friends with some local carpenters and plumbers. Ask them for an old set of bathtub drain pipes, 1 1/2" brass. Then just use your lathe to make the end caps, spouts etc. save a lot in cost of brass. Machining a tube from a solid piece of brass would scrap an a lot of the material. Now, as you got a lathe and CNC, how about making some cannon barrels?