[DonRotolo]

Practice cutting diameters on a shaft with the lathe. Take a piece of aluminum bar stock and cut some standard diameters for a specific length. For example, on a 1" shaft, cut 3/4" diameter for 1", 5/8 for another inch, and 1/2" for the last inch. See how close you can come (at least within 0.001" at 68 F).

For the mill, cut a precise slot (say, 3/4" wide x 3/8" deep). Using a 3/4" mill won't get you within 0.001 by the way...