Blender is a powerful, free tool that allows you to create your 3D objects and print them. But it’s not a tool that was built with the purpose of 3D CAD, and so there are many areas where things look fine in Blender but turn out to be wrong. This tutorial was the result of many hours of experimentation with Blender to find just the right way to do things, and if you follow these steps you should find that you can learn Blender’s quirks quickly enough.
At the same time, I am not a Blender expert, and if you have any suggestions or corrections I am eager to hear them — email@example.com.
Good luck to you in your 3D printing!