Sorry if this is the n'th repost of the same topic, but couldn't find any working answers after searching numerous topics and playing around the model for days...Yes, I'm a very newbie with Blender but putting lots of effort to learn more every day. Here is my simple model. I got it initially as a blender file but it was deeply broken and unsuitable for 3D printing. Practically rebuilt it, have deleted doubles, merged vertices etc. But still, when using 3D toolbox it seems that there are lots of non manifold edges and I just cannot figure out how it can be possible. Everything seems to be connected and closed. I'm probably missing some crucial concept of the whole Blender way of thinking. Have tried solidify, more cleaning, 3D toolbox stuff etc, but always it ends of missing some parts of the object in the STL export...sigh...please help someone to point where is my mistake. Here is the model file: Blender file
Edit: @Leander already provided a corrected version of my model, but I'm still wondering why the changes has been made and how. I have some experience working with SW, SCAD etc, and in their world my model above would be just fine. I understand the hollow/solid/parametric difference between these two, but still don't get what was wrong in my try... Here is the model how it looks after @Leander fixed it: There are now more splitted faces, the side faces (which were somehow problematic with non manifold edges) have now been splitted to several faces too. Is there some filter, script or modifier doing this or is my initial model somehow fundamentally flawed?