# Non-manifold, bad contig Edges and Sharp Edges on simple basic geometry

I have had issues trying to produce clean geometry for 3D printing for what is simple geometry. I check wether my mesh is clean or not using the 3D printing addon. Here is a step by step simple reproductible example starting with the defautl view to explain the non-manifold, bad contig Edges and Sharp Edges issues I have had and don’t understand :

From the default start:

• I change units from meter to milimeter
• I modify the view Clip start from 100mm to 0.1mm
• I delete the default cube
• I create a 10mm cube
• I add a curve > Circle radius 3mm location X 0mm Y 0mm Z 20mm
• I do a knife-project cut through
• I select the two round faces in edit mode and press 2 to have all the verticies of the two faces previously selected.
• I then bridge edge loop them I select all the verticies of the top circle and make a face (F key), notice below the 48 non manifold edge already because of that face:

• Maybe it is because the top round face makes a zero volume if that object was to be printed right now? So I do an extrude 10mm on the three “top faces” to produce the final piece, I should then have a fully solid perfectly printable piece but below are three screenshots of the issues this mesh has:

What did I do wrong for those issues to appear on such basic geometry ?

• I think I don't understand at all what happens from screenshot 3, but if you really selected all vertices of the top edge loop surrounding and holding the hole and make the face of them that surely will be non-manifold geometry no matter how you extrude it afterwards. Note that not only infinitely flat surfaces are non-manifold but infinitely flat junctions as well (e.g extrusion from selected edges on the screenshot 3). It might be easier to answer if you show desired result as well Apr 16, 2019 at 16:11
• @Mr Zak : that explains some of it. How would you transform screenshot 3 into screenshot 4 properly then (which visually is -if it were that simple - putting a cube on top of it) ? Apr 16, 2019 at 17:01
• So you are saying that since you make the face (frame 68-70 on your gif) after the rest has been extruded (or are you doing something else that looks like extrude?) then it’s ok since it will not be infinitely flat because “attached” to a volume ? I tried and still get (although it can be one-click corrected with “make manifold”) Non-Manifold Edge. On your gif what are you doing frame 231-238 ? Also how do you select so fast the vertices (frame 52-54) and the faces (frame 86-89) ? I’m afraid I didn’t quite get it although looking frame by frame at your gif. Could you elaborate ? Apr 17, 2019 at 8:39
• It is not important how is geometry created; rather the end result is. I was trying to show one example of what I thought you want to get in the gif because I wasn't generally sure if that's what you actually aim to get. What is shown in that gif can be shown in this sequence as well; text explains action for the selected geometry. Note that shown example is easier to get by just boolean cutting cylinder from a cube (which is not coming through cube) Apr 17, 2019 at 18:21
• What you describe in the sequence is what I understood after analyzing your gif. Even though I can get this geometry (the one in the gif) perfectly manifold using the Make Manifold function of the 3D Printing addon, it bothers me I can't get it manually, and I don't see what made those edges manifold since the look exactly the same before and after. This makes me dependant on an advanced tool for a simple geometry I don't understand how to make right manually, which I dislike :( Apr 17, 2019 at 20:47