Preventing the Cracking of an Ice Ball
There are several things that cause the ice sphere to crack. The primary reason for causing ice to crack is freezing it too quickly. The outside freezes first and when the inside freezes, it expands and cause the ice ball to crack.
Turn up the temperature of your freezer, wrap the tray in a hand towel, or put the ice tray in a container. Ice ball could take up to 18 hours to freeze.