I have been having problems with blender for a while now with strange things happening to my meshes. I get edges when I’m in object wireframe mode on area;s where it shouldn’t and the meshes never work right when I smooth them and the shadows are off angle at these parts. In this simple sample case pics in vid I provide I made a quick countersunk washer. This is what I’m doing exactly, Load blender defaults, add circle, 10 segments, extrude, scale down by roughly 1/3rd, select all verts, extrude z down to match thickness of a average washer, select bottom edges on new inner circle and scale down to roughly 2/3rds from starting circle size.
I shouldn’t be having this issue.
It happens during mesh construction and can be a result of how things are extruded, or when other operations are carried out. It can be unavoidable and at many times not well predicted. Just make it a practice to check your mesh once in a while and flip the normals when needed. If you want immediate feedback of flipped normals, check back face culling under the display options.
I get the same thing about every project that i work on, and its quite combersome when it comes to sculpting & materializing phases of my projects. While most people say to “select all and CTRL+N(reset normals)” on your entire wireframe, this has had seemingly irreversable problems for me, leaving me with either A: More mesh that is f’d up in the shadows or B: a huge headache (mostly both lol).
I finally fixed it by simply going to the display panel (N KEY), ‘MESH DISPLAY’ field and turning on the FACE button under the ‘Normals’ section. You can increase the size of the blue arrows, which show the direction the face normals are casting. . . . which allows you to simply select each face adversely affected (bad shadows) and click ‘W KEY’ and ‘FLIP NORMALS (Halfway down the menu)’. This has allowed me to 100% fix my problems with a clean looking model!
Polygons (by default) have two sides: outside and inside. Smooth shading adjusts lighting so that a group of connected polygons appear as one smooth surface. If some of the faces point inside and some outside, you get weird shading results.
For smooth shading it doesn’t matter if the faces point inside or outside, as long as they’re consistent. It does matter when you’re baking normals from multiple objects, because then the normals have to be consistent across all of them.
So why it doesn’t keep them consistent automatically?
Face normals gets calculated from vertex normals and you need at least 3 of them to even have a face. When you’re constructing your model, there could be any number of vertices (including 0), they might not be connected with edges and those that are, might not be filled with a face.
Making face normals consistent means that connected faces all point either inside or outside but it’s not always possible to determine which is which. If your mesh is not clean or is non-manifold (not watertight, unconnected edges, inside faces) it just can’t be done reliably. For example, plane primitive is non-manifold - there’s no inside and outside, face normal direction is decided, not calculated. When you extrude an edge, same thing.
You’re not interested in which way the normals point while you’re modeling, so it would be a big performance hit to constantly calculate normal direction without any benefits.
