How can I create this circular but non symmetric shape (in 3D)?

Question

How can I create the following shape (in 3D, similar to a torus). I only want one of the "circle shapes" (i.e not the two you see overlapping). Any ideas how one might create this?

Similar to this maybe (i.e. the difference in thinkness between on side of the ring and the other side not quite as extreme as above). I am talking about the bottom right object of the objects in the image below. Also maybe without the sharp line on top. Clarification: I need the bottom right object of the below image (or something similar to it with the first image above as inspiration), not the other open objects seen below as well.

Answer 1

A quick and dirty way is with a bezier curve.

Add a bezier curve circle, add some bevel thickness.

Enter Edit Mode, and turn on Proportional Edit. Adjust the influence radius so it reaches only three of the four curve vertex.

Select only one of the four vertex, then adjust its Radius property to zero using Proportional Edit with Alt + S.

Beware that this wont ensure both the inner and outer outline are exactly perfectly circular as illustrated in your image, but it is an approximation

Optionally adjust the number of Bevel Segments to a lower number if you want a hard edge.

You may also want to look into the Tilt property of curves for a twisting effect.

Answer 2

Edit: Comment asked for the closed shape; so I'll outline a way to do the symmetric version of it first. See the Open Shape for more details on how to do each step.

Closed shape with symmetry

• Create a mesh circle with a reasonable number of vertices.
• Remove all of the vertices from one side.
• Convert it to a curve.
• Create a mesh circle with three vertices.
• Edit it to the profile shape you want.
• Create a Bezier Curve. Edit it to be the profile shape.
• Set the taper and bevel objects of the half circle curve to the profile and triangle.
• Add a mirror modifier.

Here's an example:

Open shape

I would do this by relying on a curve's bevel and taper properties. Here is one of the open circle designs done this way:

• Create a mesh circle with a reasonable number of vertices. For the example I've chosen the default 32.
• In Edit mode delete a few adjacent vertices to create the gap. For the example I've chosen just one:
• In Object mode convert it to a curve using Object → Convert → Curve menu entry.
• In Object mode add another mesh circle but give it 3 vertices to create a triangle.
• Edit the triangle to get the narrow profile you want. This will become the shape of your 3D object. Scale it down and apply scale.
• In Object mode convert it to a curve.
• Select your first curve and go to object data properties.
• Open the Bevel panel if it's not open and select "Object".
• Set the object to your triangle shaped curve. I called mine "triangle".
• In Object mode add a Bezier curve.
• Go back to the original curve, and open the Geometry panel if it's not open.
• Set the "Taper Object" to your new Bezier Curve.
• Edit the new Bezier Curve to get the taper you want. Here's one that goes smoothly from one end to the other, leaving a small opening at the tip. (I used automatic vectors to get the straight line.

Here's my hurried version. With a bit of editing on the triangle and the Bezier taper you can reproduce any of the shape except the closed one.

Answer 3

For that last shape you need a circle curve that is not cyclic, so it's final point needs to be in the same position as the starting point.

Here I moved the end point to show that it's not cyclic:

Then you tilt the curve points from start to end, starting with a tilt of 0 and ending with a tilt of 180.

After that, you adjust the radius of the points.

Now the curve bevel:

If the curve will have smooth shading, add a weld modifier so the curve's start and end connect.