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I am modelling a robot head that looks like this:

enter image description here

The shape was obtained by using very few faces starting with a square.

Now I would like to add a nose to the robot that would look more or less like this:

enter image description here

But instead of this screenshot which was obtained by adding a second triangle shape onto the head, I would like to model it from the head's mesh.

Here's the head in edit mode:

enter image description here

If I add vertical or horizontal loop cuts, the base shape of the head becomes larger where the loop cuts are added. I would like to extrude a face outwards where the middle of the face is, but there is no face there, and I only know how to add one by adding loop cuts.

It is important for me not to lose the almost spherical curvature of the chin and sides and top of the head... And obviously I would like not to apply the Sub Surf modifier because I am trying to keep the model light and easy to edit...

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  • $\begingroup$ You're already using a subsurf modifier to get that shape. $\endgroup$ – Anthony Forwood Sep 13 '16 at 5:34
  • $\begingroup$ @AnthonyForwood I know. I'm not sure what you're saying... I am trying to create a face in the middle of the head that I could extrude out and crease to make its edges sharper... without adding loop cuts all around. $\endgroup$ – MicroMachine Sep 13 '16 at 5:58
  • $\begingroup$ You said you didn't want to use one, but you already are. $\endgroup$ – Anthony Forwood Sep 13 '16 at 7:26
  • $\begingroup$ the thing is, you can't edit an interpolation directly... perhaps you could model the nose independently and at last join meshes or something like that... $\endgroup$ – m.ardito Sep 13 '16 at 7:36
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Your mesh is so "Low Poly" that every nev vertex will interact with the subsurf algorithm, modifying the overall shape; but you need some extra vertices for the nose; so the solution is: RETOPOlogizing. Create a new object (I.E. a plane), set all the little buttons circled in red and start moving and extruding vertices: every time you move a vertex it will snap onto the surface underneath. So you will be able to put how many vertices you want, exactly where you want, without modifying your shape. Useful also for good deformation topology, if intended to be animated.

enter image description here

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  • $\begingroup$ Your solution is interesting, but the way you are retopologizing the mesh seems almost identical as the result that you would have by adding a Subsurf of value 1, and applying it. $\endgroup$ – MicroMachine Apr 18 '17 at 21:19
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    $\begingroup$ This is only an example of the retopo worflow: the great advantage of retopo is exactly the fact that you can put vertices exactly where you want, with any kind of edge rings flow. It's good also the fact that you can split your attention in half: at first you do the model, without any topology worries; then you can set all your attention to the topology, without caring of the shapes, which are already established. Nothing that a subsurf modifier can do. $\endgroup$ – josh sanfelici Apr 19 '17 at 19:46
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Select the four front faces of your head and use the Inset tool to create four inner faces, like this:

enter image description here

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  • $\begingroup$ Thanks! For a second, looking at your screenshot, I thought there was a web-based version of Blender. $\endgroup$ – MicroMachine Sep 13 '16 at 16:01
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I've found Subsurf modifier to be a bit of a dark art at times - especially with seams and transitions between different sections of the model. This method seems to work for me.

Starting with your existing mesh, go into Edit mode and use the knife tool to add cuts to start to create the nose. This will affect the underlying surface but don't worry.

enter image description here

Next, move the newly added vertices back so as to restore the original curve - in this case you should be able to simply move them straight back along the axis. Adjust them until you've got your original shape back.

enter image description here

Select the new faces and extrude ('E') - don't move the extruded faces, just accept them where they are. Extrude again and this time move the new extruded faces forward. Your old mesh should remain unchanged (as it's protected by the extra band of faces) while you can extrude the nose.

enter image description here

Tweak the edges and vertices until you get the shape you require.

enter image description here

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Combining the different answers, I came up with this solution:

1-Too low poly

Josh suggested that the mesh was "too low poly". He's right. But instead of retopologizing, I decided to add a Subsurface Modifier with a value of 1, and to apply it. It keeps the model simple and light, and doesn't deform the general shape.

enter image description here

2-Knife, Inset or... Bevel?

Rich suggested to use the Knife Project tool. It's a good idea, but also a bit imprecise (unless used in conjunction with a Mirror modifier). Anthony suggested the use of Inset to create faces in the middle, which was also a good suggestion, but created too much geometry gathered in the middle (instead of just one additional face) and new faces that are square.

These directions were good, but instead I decided to Bevel the first lower vertical edge by selecting the edge and using CTRL + B, thus creating two triangles and a square face. Then I Extrude the triangle-shaped face, Scale and adjust, then add a Subsurface Modifier:

enter image description here

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