Summary:
I first ran across this project while browsing google photo's for "machining projects" and it seemed like a great way to get some practice dealing with backlash on the mill. When I ran across 3 aluminum disks in one of the shop scrap bin, it was a no brainier second project.
For this project I wen't with with a simple 5x5 pyramid, but in principle one could cut a much more complicated base pattern. Spheres pack pretty well hexagonally as well. I still have 2 more disks, so at some point in the future I may make a variant of this project with a more complex hole pattern.
Like any good second project, this one involved a fair number of "learning opportunities" along the way. Most will be obvious to a more experienced machinist, but I have included a short list below.
Lessons Learned:
When making a super glue arbor it is important to cut grooves to hold the super glue. Otherwise, the glue tends to bunch up and prevent the piece from sitting flat. (If I was doing this again I would use soft-jaws instead of a glue arbor).
Freshly cast aluminum is very "gummy" which makes it a bit tough to work with. Fine for making the arbor, but if other choices exist those'd be better.
Double check that the end mill used is a ball nosed rather than a bull nosed.
