A fun milling machine project for you...
1. Take a block of aluminum (or whatever you like) and machine a cube with dimensions of 2.000" x 2.000" plus/minus .001
2. Locate center of each side and bore a 1.000" diameter round hole on each side of the cube to a depth of .500"
Make sure your set-up is rock solid and the soon to created inside cube is well clamped and supported. Good set-up practice...
Finish up with a boring bar set-up to clean up. Hand manipulation of the mill table will be needed.
3. The resulting cube inside of a cube will mess with the average persons mind. Truly fitting a square peg through a round hole.
Don't forget to break all edges and de-burr as required and use all appropriate PPE.