Help modelling curves on a spherical object

What methods should I explore for creating curves on a UV sphere to extrude? I’ve been selecting faces and extruding them inwards but this is squarish and I’m not sure how to control the elliptical shape which I then plan to extrude in. I have also tried creating tri’s through the faces to get curvature but the lack of angling control over the top and bottom lines is frustrating. Is there a method to draw such a shape and then extrude inwards?

Here’s a sketch. Note the ellipse in the sphere. I’m trying to get this sort of shape and then (maybe?) extrude inwards with some beveling or subsurf to round it in.


Hey, There is the ‘Knife’ tool in ‘edit’ mode - K key is the short cut

Hey ajcdfin, thanks for the tip. I didn’t know about that tool or shortcut. I’m experimenting with it right now and it seems useful.

My tests are failing to get the geometry. I’ve attached an experiment with the knife tool and extrusion on a UV Sphere below. I think I’m approaching this problem with the wrong method and thought. Here is an example of the type of sculpting geometry I’m going for. Notice how smooth the bottom line of the mouth is in this sculpture? Mine is very diagonal and sharp. Maybe I need to forget the extrusion part and focus on getting the curves appropriate on the face? And then once those are in place create the inner topology somehow.

Looking at this work some more maybe I need to join the faces somehow and then curve the connected edge. Maybe the proportional edit can help. Hmm.

Hey, It looks like you cut vert to vert - you can cut and add verts anywhere on a ‘face’ also. Try this, in object mode add a ‘curve circle’, edit it to the shape you want the mouth to be in ‘edit’ mode, select sphere and add a ‘shrinkwrap’ modifier and choose the curve object, keep above surface check box, position it where you want, now you can go into edit mode(sphere) and you will have a guide to use the knife tool.
If your using a ‘subsurf’ modifier it will help smooth things out.

WOAH! Now I made progress thanks to you. I understand now what you mean about cutting anywhere on the face instead of vert to vert. Here’s what I was able to come up with:

For some reason when I used the “shrinkwrap” modifier it appeared jagged on the sphere. I might have done something incorrectly. Here’s the circle I drew and edited:

And here’s how it appeared:

This is all very interesting and a lot of information to process.

I think the circle deformation is the result of squishing it in edit mode in combination with deformation from shrinkwrap onto UV Sphere. I can slightly further calibrate it once it’s attached to UV Sphere.

Is there a method to make “symmetrical cuts” with the knife so that I don’t have to work on both the left and right halves of the UV Sphere?

Cut the sphere in half, and use a mirror modifier.

Thanks Speedthriller, I haven’t experimented with this. I will try it out.

I’m making progress thanks to everyones input. Blender is very fun and also very complicated! Now I’m facing sloppy edge problems due to what I think are ngons. Smooth shading makes it terrible and a lot of subsurf seems to make it alright but still very noticeable. I’m not sure how to proceed with this to get more perfect curvature around the cut. Does anyone have insight or references as to how to create smoother edge flow? I’m not sure if that’s the right question. I’m guessing what I want around the cut is more quad(?) faces and I have created a lot of jagged complex faces.

Hey, If you select just the verts that make up the circumference of the mouth, Loop Tools Add-on > Space (that will space them evenly) > Extrude (E key) Enter > Scale (S key) just a little bit. Now you will have a nice edge ring.
Check out these sites if you have time - lots to learn there.

Thanks so much for your input ajcdfin it is helping me a ton. I’m reading through this and experimenting with what you mentioned above. It’s a lot of information to take in.

I’m not sure where I’m going wrong here. This is the starting point before I use Space/Extrude/Scale:

Adding the Loop Tools Space adds some distortion which I am guessing is normal:

And I end up with these slight distortions and pinches. Here’s the result:

From reading the topology guide I think it’s because my geometry has become complex with ngons or poles. I’m wondering if there’s some other “smoothing” or tool I can use to gently round out this distortion.

Perhaps, an ege loop around your cut could create a cleaner hole.

Your sphere is already very detailed, makes fixing topology more complicate. L-Shaped NGons could be split into 2 quads easily.

Leonard_Siebeneicher, interesting idea. I think I understand and I’m going to experiment with what you say here. The sphere shape I cut above is a cube, I was hoping the quad toplogy would make the task easier but no success so far.

I can also see from your image that you appear to be working with less vertices which may make this job easier.

Yes, more verts could make it more complicated.

Mh … if you like, you also could use a pole or an inset scale to your advantage. The idea is to use pole (inset scale) together with “EditMode//intersect (Boolean)”.

Pole could be created by extruding a surface (set of faces), and merge all vertices at center.


In the video I used a 10x10 grid and a (x-scaled) cylinder.

I am experimenting with all of your suggestions right now. As a side note I must say, wow, what a difference a lower vert count makes for observing a structure! I was ignoring this critical aspect upon object creation and can see how important this is.

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