A local rider and friend of Ruckus broke his SRAM XX rear derailleur awhile back. The part that broke was a slightly wussy nylon cable guide, all his attempts were sadly futile to find a replacement part.
To continue honing our abilities to mill and lathe aluminum I decided to take it on and see what we could do. We ended up with the shiny piece of aluminum in the red box. It was a fairly intricate part with a seemingly endless variation of pockets and holes to mate up. Our first attempt had too much metal ( is there such a thing?) and the rider could only get into 9 out of his 10 gears but with a little tweaking he can now shift across the broad range of his mountain cassette. It was a fun little side project to distract us from our standard day of carbon fiber(ing) everything and help us hone our metal working skills.
Also I have decided that I like to polish aluminum, it just gets so darn shiny.