Why does this happen?

Question Modeling

Hi!

So I have a question.

When I try to extrude a single plane (model 1) I get a box shape.

But when I extrude an edge from a box (model 2) and then try to extrude that plane I get a hole.

I should probably know this by now, but can someone please explain to me why this happens? :)etr.png

1 love
Reply
  • Omar Domenech replied

    I'm not sure why is that, but in my mind is enough that I know it is how it behaves, so I work of off that. There might be a technical explanation, something about the edge being connected that makes the operation behave differently? I'm not sure, Martin might know.

    2 loves
  • Omar Domenech replied

    But don't worry, most of the masters don't mind that kind of things either. You say you should know by now, but nah, it's like owning a power-drill, you don't know how the thing works, you just know that you can use it to make a house with it. Well not a house, but stuff around the house, it makes jobs easier. Master builders use the tools all the time, it's not expected of them to know every in and out of a tool. So you don't need to necessarily know technical Blender stuffs, the end goal is art.

    1 love
  • Martin Bergwerf replied

    Hi 5546_student ,

    This is not something you should know by now 😉

    It's a good question though.

    It's because of how the Extrude algorithm works and the main thing, is the difference between boundary Edges (connected to exactly 1 Face) and internal Edges (connected to 2 or more Faces):

    Extrude.png

    Here's what the Manual says:

    Extrude_man.png

    So, for most Blender users, nothing to worry about.

    3 loves
  • 546_student replied

    Oh, that makes sense. So it's just how Blender is built kind of? I thought maybe I was doing something wrong when modeling, and needed to use another way to extrude. Does that mean that it's impossible to get a complete box if you extrude like this (model2)? Do you have to do it another way?

    I will to try to understand it, :) hehe

    1 love
  • Leo (wod) replied

    I think this has to do with the additional geometry. If you have the lower cube geometry in Model2, blender sees the extrude in the upper face as an extension and only extrudes the actual face. Model1 is standalone BUT I don't know either :) 

    What I do know is that if you select CTRL+E and Extrude Edges or simply select Edge Mode -> select Edges and then E, you can work around this. You just have to know how to help yourself

    2 loves
  • Leo (wod) replied

    Damn. The others are always faster

    • 😉
    3 loves
  • 546_student replied

    I tried to do the edge mode extrude like you suggested, Leo, but I couldn't get it to work. Maybe I did it wrong :)

    I think I sort of understand what the manual says, at least I know it's not something I modeled wrong, it's just how it is,

    So thanks for the help, everyone!

    • 🤘🏻
    • 👍
    1 love
  • Leo (wod) replied

    Just like that. But you don't need to use CTRL+E -> Extrude Edges. If you are already in EdgeMode, you could also simply select the edges and then extrude them

    Nice that you can also upload gifs here :)

    5-04-25 20-36-46.gif

    2 loves
  • 546_student replied
    Oh, that gif helped me see what I did wrong! Thanks :)

    I thought I was supposed to select 4 edges, and not 3 like you did. The model get's hollow inside, but I suppose that's to be expected and I would have to build the rest right?
    1 love
  • Leo (wod) replied

    You can create faces with the F key. So select Edges and then F. Your Model 1 is also "hollow", you can zoom in on it - that's normal.

    It all comes with time.

    2 loves