# How can I rotate/twist a torus about its major circle?

The problem: I am building a torus with an intricate regular pattern that includes a twist. A simple example: http://netz.smurf.noris.de/blender2.png

I have built one torus segment – my "real" example is obviously a lot more intricate, not just a simple inset operation.

Now I want to transform the left segment into the right one. The end goal is to do that six times so that, in this example, I get a torus with a doubly-winded spiral around it.

• Do you mean you have a cylinder and want to bend it in order to make from it a part of torus ? It's easier to do if original cylinder isn't rotated / twisted. Feb 17, 2016 at 15:01
• No, I already have a sixth of a torus. If there's a way to straighten the thing that doesn't involve moving a whole lot of vertices manually …? Feb 17, 2016 at 16:50
• I think you really need to find a picture to show us the end result of your model. Your description is lacking, I am afraid it's very difficult to understand what you are looking for. Feb 17, 2016 at 17:13
• I have changed the image and extended the description. Feb 17, 2016 at 17:57

## 3 Answers

As far as I know, there is no easy way to rotate about a curved axis. Your best bet would be to model the segments straight, use an array modifier, then bend them.

First model a straight segment of the object.

Next add an Empty to the scene and position it at the end of the segment. Then add an Array modifier to the segment, and uncheck Constant Offset and Relative Offset and enable Object Offset, selecting the empty as the offset object.

The Array modifier works by duplicating the geometry of the mesh and placing it at the position of the offset object, further parts of the array copy this relative transformation.

Now add a Simple Deform modifier to the object and set it to Bend with an angle of 360°. You will probably also have to add another empty and use it as the Simple Deform origin so you can rotate the axis being bent around.

You can adjust the diameter of the torus by increasing the Array count. Note that since my example model is 90°, I need to use multiples of 4 for the array modifier so that the teeth line up at the seam.

• Thanks for the elaborate answer. This does seem to mean that I need to re-do my design on a cylinder. Any good ideas how to straighten the torus segment out? A "wobbly" result would work for me. Feb 18, 2016 at 2:52
• @MatthiasUrlichs You could add a Simple Deform modifier (set to bend) to bend it straight. You would need to do some math to figure out the exact bend angle. Feb 18, 2016 at 2:53

1. Draw the Desired Profile

2. Add the Screw Modifier - For the Screw Amount, be sure to calculate the Circumference / Arc Length.

3. Add a Bezier Circle / Arc

4. Apply the Screw Modifier, rotate about the Center of Screw Object to lay parallel to the Bezier Circle, Then position the Screw Origin to the Bezier Circle's Origin.

5. Add the Curve Modifier to the Screw Object, and for the reference object, select the Bezier Circle.

• Umm, no. I don't want to rotate around Z (I know how to do that …), I want to rotate/twist around the major circumference of the torus this is a part of. Feb 17, 2016 at 16:47
• OK, I will revise my answer to suit your needs. Feb 17, 2016 at 19:58
• One more thing, to control the resolution change the 'Steps' value. Feb 17, 2016 at 20:10
• This doesn't answer the question, the OP is starting with a 3d object that is a curved cylinder. This doesn't address that anywhere.
– dval
Feb 23, 2016 at 15:45
• @dval - Read the question again... "The problem: I am building a torus...". What part of "I am building" says that the OP is starting with the 3D object 1st? Feb 23, 2016 at 18:04

Modelling

• A cylinder plain or elaborate can be made first, then add a [Curve Modifier]. Cylinder first, then curve it.

Above Example 1

Above Example 2

• Hmm. I have updated my question; could you elaborate? I don't quite see how a twirly knotted torus can transform my torus segment into something that's twisted but not knotted. Feb 17, 2016 at 18:05