Lecture 33. Question on extrusion

[StevenNani]

I can’t get past the way Mike uses extrusion to make a slope. Suddenly I don’t understand how extrusion works now. I’ll explain with a few examples.
Mike’s way:

1. Select the Faces.
   

   

2. Extrude and Esc(create new geometry).

3. Select the Edges.
   

   

4. Move them by 1 unit(in x or y direction) so that the two edges of the face coincide giving us a slope.
   

   

Now, how I understood Extrusion works is it creates new geometry and this is how it should work.

Create a new geometry, in this case even if I move the newly created edges there should be another edge in its place. I am going crazy for the past few hours trying to understand why and how extrusion works differently for two seemingly same models?

[NP5]

You are right. I have tried it as you have shown.

The second set you are using is only a plane, so the extrusion leaves a full copy behind it to ‘thicken’ the plane. But on a solid object extrude has a solid foundation to raise up from and does not create what would be internal geometry if it acted like on the plane.

See image.

Extruding and moving to separate out the created geometry so we can see it, shows how a solid two apparently the same faces does not need to create the internal edge, white active selection in the image. But a plane needs to as it is the ‘back’ of a newly made solid from a plane.

SO, on your ‘plane only’ extrusion steps, there is that extra edge created, that remains in place when you slide the newly created one back. However, it does not exist to stay there when the extrusion is done on the solid object, pyramid.

An interesting conundrum to work out!

[StevenNani]

Yeah, I have thought the same too but wasn’t sure. So, extrusion works differently for solid and plane meshes. Thanks for the info.