I just love machining lowers. After my success with polymer I just had to try aluminum. Here is my new finished lower made on a 7075 billet. I finished the lower using an easy jig from 80% arms. After a little modification to the side walls it works with all lowers I have put in it.
My recommendation is to go slow, use lots of lube. Best thing is that I used a small hand router not a mill.