So maybe you want to make large spherical ice for drinks. And you have a 3d printer, so you want to use it. Only if you just print an ice mold, the plastic may or may not be food safe, so you aren't so sure about that. So you want to 3d print a mold that you can use to make a mold out of a food safe mold making material, such CopyFlex from www.makeyourownmolds.com. Furthermore, you want to be able to pick the size of your ice sphere. If all that is true, you have come to the right place. Customize this to the size you like, print it (it is an easy print, no supports needed, etc.) with any material you have handy, pour your mold making material into the mold you just printed, and start making ice.

A few notes: spray your 3d printed mold with cooking spray so it is easier to get the mold out. I ended up destroying my 3d printed mold in the process. Maybe you are better at it than I am.