In this lesson video, we are going to discuss the common problems usually happen in a 3d modeling process. I've been teaching 3d for more than 17 years now when I record this video, and throughout those years, I've seen the same problems appear again and again in my students works. So I decided to create this lesson to explain these common problems and how to fix them. There are a total of five common problems I want to discuss. Three of them will be discussed in this lesson and the other two problems will be discussed in the next two lessons because they require a more in depth explanation. The first common problem is the bevel modifier not working as expected to be a few examples.

Here I have three cubes. At a glance they look identical. If I select this one and add a bevel modifier, I can slide this with a value all the way until the cube looks like that. pyramids are also known as an octahedron. Now, if we select this one and try to do the same, sliding, the width value only works to a certain extent. After that certain value, the bevel modifier seems to stop working.

The last cube here is even worse. If you add a bevel modifier on it, it just doesn't do anything. So what is actually going on here? Well, something that you need to understand about the bevel modifier is that by default, it will not add a bevel with more than the smallest age gap you have in your model. If we look at the first cube, and go to the Edit Mode, let's turn off this edit mode Preview button. The ages in this model are clean.

There are no ages touching each other or positioned to close. Now, if we look at the next model, let's turn off this preview button also. We can see we Have this age and this age close to each other creating these very small gap. This is the reason why the bevel modifier cannot go any further, because if you push it beyond the size of this gap, the geometry will break as the ages will overlap. Now, you might be wondering, what if I want to make the ages overlap? Can we do that?

Well, yes, we can. Although I wouldn't recommend it. In the bevel modifier, you can see this option clamp overlap. This is the option responsible for detecting overlapping edges and then limit the width to avoid that overlaps. If you go to the object mode, and then turn off this clamp overlap option. If we have a large value as the width larger than the existing each gap in the model, we can get something like this.

Most of the time, you don't want this to happen to your model. So I always have this option turned on and I rather have fixed the model such as resolved The unwanted edge loops or slide them away to remove the small gaps. This will make sure we have a good geometry in our model. Now what about the last cube then, if we look at this cube in the edit mode, it seems Nothing is wrong. But if you select this top face and then press G to move it, we can see that this object has an overlapping mesh problem. This seems strange, but believe me, this problem happens a lot to my students.

Let me turn this off. Also, the most common cause why this is happening is the use of select a face and then press E to extrude. But then in the middle of the process, you change your mind and cancel it by pressing the right mouse button. It looks like you just cancel the extra operation. But in reality, you only cancel the face movement. The extrusion already performed so to fix this issue.

If you want to cancel the extrusion, after you right click to cancel the movement, you also need to press Ctrl Z, this will undo the extrusion. Now, what if we already have too many of these double measures and the Undo command does not apply anymore? Well, you can use merge by distance operation. To do that, first select all of the vertices you want to merge, you can just press A to select all and then press R m, this will open up the merge vertices sub menu, just by distance here. This command will merge the vertices if the distance between them is less than this value here. As we can see, now the bevel modifier works as we expected.

The second problem is the double mesh elements as we discussed previously, one of the reasons why this can happen is because we do extra but then we can isolate with right click besides that means Other things can cause this double mesh problems, for example, trying to duplicate mesh elements, but then cancel it. If I select this face, and then press Shift D to duplicate, and I try to move this duplicated face to another location, but then I changed my mind and right click to cancel what actually happened here, I just cancelled the movement, not the duplication. You can see if I select this face and try to move it, we have double faces in this location. To fix this issue. It is basically the same as before, you need to press Ctrl Z if you want to cancel the duplication, or you can use the merge vertices by distance method, which is our M for the shortcut.

If you forget the shortcut, you can open the vertex menu up here, choose merge vertices, then by distance. Or another way to do this is by going to the mesh menu up here. Then to cleaned up and then merge by distance. The next common problem is using the F shortcut on existing topology. If you have existing topology, then you should use the J shortcut instead to connect vertices not the F shortcut. We have discussed this more in depth before, so please check the previous lesson about connecting vertices if you forget about this topic.

The last two common problems in 3d modeling are flip normals and non manifold geometry. Now, because these two topics are too deep to be discussed briefly in a single lesson, we will discuss each of them in separate lessons.