I've already made my enthusiasm for Tree sprockets public so this is just a little follow up.
This is a video of the making of the Tree splined sprocket at that hub of bicycle machining known as Super Rat Machine Works. If you haven't looked at the Super Rat site before, take a look. It's full of raw metal machined bicycle porn.
But anyway... here you can marvel at how a square bit of 7075 billet, with the help of seven different machining tools and some extra trickery, is transformed into the best sprocket on the market.