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How can I get the walls of a cylinder to extrude (E) with the top faces of the cylinder? Tried selecting faces, faces and edges and faces and vertex. The attachment shows the top face partly extruded down the cylinder leaving the outer shell faces at the top. Thank you enter image description here

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  • $\begingroup$ The problem appears to be caused by a second cylinder or skin occupying the same space. Not sure how this happened but it should be easy to track down. $\endgroup$
    – Barrie
    Feb 23, 2023 at 23:20
  • $\begingroup$ Default extrusion never reduces geometry, it always expands. You don't even have to move the faces in any direction, it is just convenient to do it in one step. You could also hit E and then Esc, the geometry is then added but stays in the original location. Moving with G on the Z axis up then creates what you get with extruding up, moving with G on the Z down creates what you get with extruding down. The Extrude tool only spares you hitting G and Z twice for normal direction. If you didn't want to move, you could hit S to scale or R to rotate. Moving is just what it does by default. $\endgroup$ Feb 24, 2023 at 8:03
  • $\begingroup$ @Robin Betts Thanks for the edit. I will take care to select the right button next time. $\endgroup$
    – Barrie
    Feb 24, 2023 at 19:05

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Extrusion is usually an expansion of a mesh - so it is absolutely normal that it doesn't reduce faces. And since the connected vertices are further up than the new faces, well - they leave a shell. Also Blender doesn't know what you want to do - you could go on by scaling the extruded faces smaller and have some sloped structure afterwards.

But there is a tool in Blender which is made to prevent extrusion that creates non-manifold faces: if you press Alt+E and choose Extrude Manifold it does exactly what you want and removes the shell faces.

extrude manifold

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  • $\begingroup$ Many thanks. That's exactly what I needed. Haven't used Blender for 6 years when I gave up due to its steep learning curve. Now very motivated to leave Sketchup for Blender. $\endgroup$
    – Barrie
    Feb 24, 2023 at 18:57

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