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I have some questions. I need answers, Please.

1- If an extra face exists inside of an object why it is considered as a problem? Nobody is going to see them, right? Why we have to remove it?

2- Extrude a face vs. select a face and then ‘G’ and then drag that along with any axis – what is the difference between these two procedures?

3- Scaling an entire object in Edit mode and scaling an object in object mode is there any difference between these two?

4- So if number one is right procedure (to eliminate extra faces) then why sometimes when we insert one object into another and keep modeling, without erasing the overlapping part- that is considered okay. Nobody seems to bother in this case (attached image).

enter image description here

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  • $\begingroup$ 1- Who said it's a problem? Extra faces can become issues in specific situations, but that's not an absolute rule. $\endgroup$
    – Alexandre Marcati
    Jul 7, 2022 at 14:55
  • $\begingroup$ Okay. In a tutorial the tutor kept erasing extra vertices. But he is okay with overlapping. So I am confused. $\endgroup$
    – Russian Blue
    Jul 7, 2022 at 15:04
  • $\begingroup$ It's impossible to tell why he was erasing the vertices because I don't know the context. You'll have to be more specific. $\endgroup$
    – Alexandre Marcati
    Jul 7, 2022 at 15:06
  • $\begingroup$ youtube.com/… $\endgroup$
    – Russian Blue
    Jul 7, 2022 at 15:09
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    $\begingroup$ In that case the problem is not that there is a hidden face, the problem is that there ware duplicate vertices creating faces that were as thin as an edge (so they had zero area). This can happen when you extrude and cancel the extrude and doesnt undo after. It's an issue because it will cause shading problems. Also if you use a modifier like subdivision surface, it will be glitchy in that area. $\endgroup$
    – Alexandre Marcati
    Jul 7, 2022 at 15:19

3 Answers 3

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  1. Who said it's a problem? Extra faces can become issues in specific situations, but that's not an absolute rule.
  2. Extruding doesn't move the existing face, it creates new faces that extrude out from the one you are extruding from. This might not seem clear if your extruding a whole side of a cube, but try subdividing the cube and then extruding only one face vs. moving the face and you will understand the difference.

Let me illustrate. My cube:

enter image description here

Moving one of the faces up:

enter image description here

Extruding that face instead of moving it:

enter image description here

  1. Yes. When you scale the object in object mode you are changing the scale parameter of the object. This can make modifiers behave differently because it's as if they change the object in base scale, so things like the bevel modifier can get stretched or seem to be at the wrong scale if the object's scale is different than 1, 1, 1. When you scale the whole object in edit mode you are actually moving the vertices, and the object's scale parameter remains the same.

  2. I think you are trying to extrapolate from a specific case when someone told you an extra face was bad. It's not always the case.

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    $\begingroup$ Thank you so much. I understand now. How did you make your grid like that (light ash). it's so cute. How can I do same. this black grid line makes blind. $\endgroup$
    – Russian Blue
    Jul 7, 2022 at 15:06
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    $\begingroup$ It's not my grid that is light ash, it's the background. I'm using and HDRI image as the background in the world shader. $\endgroup$
    – Alexandre Marcati
    Jul 7, 2022 at 15:07
  • $\begingroup$ Hey, if you think my answer was helpful please upvote it and mark it as the solution by clicking the check mark, please $\endgroup$
    – Alexandre Marcati
    Jul 7, 2022 at 15:08
  • $\begingroup$ How can I change the background? $\endgroup$
    – Russian Blue
    Jul 7, 2022 at 15:10
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    $\begingroup$ Thank you soooooo much. $\endgroup$
    – Russian Blue
    Jul 7, 2022 at 15:16
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To add to Alexandre Marcati's answer, inner faces are bad in single meshes, because if you give your object a Subdivision Surface modifier it will create artefacts:

enter image description here

Also you won't be able to create a loopcut on this part as a loopcut can't cut through an edge that is common to more than 2 faces:

enter image description here

enter image description here

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  • $\begingroup$ Thank you Moonboots. Yeah now I know. $\endgroup$
    – Russian Blue
    Jul 7, 2022 at 15:33
  • $\begingroup$ :O Super cool answer. $\endgroup$
    – Russian Blue
    Jul 7, 2022 at 16:26
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I'll give you simple answers:

  1. This may cause further simulation errors. For example, you want to select a vertex in the middle of an object, and there is another polygon inside. And you will select not the vertex you need, but the one that belongs to that polygon and continue modeling. And it's good if you immediately notice the error.
  2. Large. Face extrude adds extra vertices in the same place where it was, but G does not. In fact, Extrude is the main modeling command, and G(move) is just a transformation of an existing mesh (moving vertices and nothing more).
  3. Yes. When scaling in object mode, you change the Scale parameter in transformations, but when scaling in edit mode, it doesn't. Sometimes this is needed when animating, for example, when you create visual images of bones from meshes. But if you're just starting out, just don't worry about it just yet.
  4. This is normal for static compositions. For example, visualization of interiors, etc. In general, the renderer can calculate object intersections. But for scenes with animation, this is also not suitable.
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  • $\begingroup$ Thank you for you kind reply. $\endgroup$
    – Russian Blue
    Jul 7, 2022 at 16:06

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