The link above shows a series of videos that I have published while working on this project. The videos start with unpacking the 3D printer that I used to to make an ar-15 lower receiver. Each video showcases a different stage or problem I faced during this project.
Without extensive knowledge about firearms and 3D printing, I would not recommend that anyone should attempt this project. Firearms parts produced by a common 3D printer are not an adequate substitute for professionally manufactured parts.