How to make a 3D Printed Mold Using Blender.

I'm adding this to my other series of how to use blender located under my things. I feel this is a separate thing because it would be a little easier to search if your looking for just this information.
https://www.youtube.com/watch?v=X2NHIACfUhU
This video shows how to take a model from thingiverse and turn it into a mold.
Later I'll make another video that shows how to make a mold that is more complex and requires sprues, but for now here is the first step to making non complex molds. aka things with flat bases.

I hope you enjoy.