Download the Drawing Rifling.jpg and print it out before reading this article. The tool has two parts. Part one, a frame for holding the cutting tool is mounted to the saddle. The cutting tool is rotated by a rack and pinion mechanism, with the pinion gear attached to the rod that holds the cutting tool. Part two, the rack for the pinion gear is bolted to the cross slide.
Most Lathes have two tapped holes on the tail end of the saddle for mounting a follower rest.
You will need to drill and tap comparable holes on the head side of the saddle to mount the frames. Use spacers if necessary to insure that the cross slide can clear the frames. I did not show my braces between the upper sides of the frames because the drawings are already muddled enough. There are two independently rotating assemblies that are only connected by the index pin. Set screws secure them together.