When you are using the calf press machine, adjust your foot angle each time you go through the circuit. That is, point your toes in a different direction—inside, outside, and straight up. You can also move the balls of your feet to a different spot on the pad.
These variations will cause your muscles to move differently as your ankle and knee joints pivot due to the changes in angle and placement. Why is this important? You don't just want muscles, you want big, round, full muscles, and that comes from stretching muscle fascia and fibers in various manners.