Not at all. It's nice to have but you can just cast without it. I've got a vacuum desiccator that I bought with a vacuum pump and honestly, I wish I didn't now. The bubbles are typically so small, you can't see them and you can fill imperfections with Sculpey or epoxy putty. I could see using a chamber if you're doing miniatures or things that have extremely long and thin parts like the string on a bow and arrow that needs to be replicated like Artemis' bow accessory. Things like the two halves on a torso would probably also do better with one of those but things like headcasts and even other body parts like closed fists, you'll be fine with a cheap kit of silicone mold mix and RTV resin.