Here's a method that gets ice balls started using the cooler method for making clear ice. This comes courtesy of Dave Michalowski, for I saw it on his Facebook page and asked if I could steal his pictures to share. Thanks Dave!
He says, "I am using the round containers for the ice balls. I got them at the Container Store and they work perfectly. I believe they are three inches across and will snuggly fit into most old fashioned glasses. I saw off the end off the cylinder so the air doesn't get trapped in the bottom."
Dave carves his spheres from the cylendars using a Japanese paring knife, something I've not been brave enough to try yet.