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I'm trying to extrude a circle along a circular path, ending up with a torus.

First, I added a Bezier circle centered at 0,0,0 and made it 10x10 in width and height (to form the path), then I added another circle, also at 0,0,0, and made it 2x2 in size.

When I select the smaller circle as the Bevel Object of the larger circle, the resulting shape resembles a swollen torus with a slight depression in the centre (where the hole would be) and becomes 20x20, larger than I expect.

I've tried positioning the smaller circle in different places, and at different angles before setting it as the Bevel Object, with similar results.

Any ideas what I'm doing wrong?

Here's an image of the two curves, then the end result:

Two curves: the large on for the path and the small for the cross section

The result

Update

Just in case it helps anyone else, I think my problem occurred because I was scaling the larger circle (the path for the extrusion) via the Transform panel in Object mode rather than Edit mode.

Instead, if you add the (larger) circle, change to Edit mode and scale it to the correct size, and then change back to Object mode and set the Bevel Object, everything works perfectly.

Not sure if it's related, but a response on another site implies that you could also scale in Object mode, then Apply -> Scale, though this didn't work for me.

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  • $\begingroup$ sorry to ask the obvious... why not just add->Mesh->torus? $\endgroup$ – user1853 Dec 16 '13 at 7:38
  • $\begingroup$ Because the OP wants a curve object. Adding a torus results in a mesh object. $\endgroup$ – gandalf3♦ Dec 16 '13 at 7:42
  • $\begingroup$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. $\endgroup$ – Gunslinger Dec 16 '13 at 11:31
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If all you want is a torus, then iKlsR's answer is the way to go. To answer your question, it sounds like the beveled curve is only scaled in the X and Y axes.

To create a torus with a bevel object:

  1. Add two Circle curves.

  2. Set the bevel object of one curve to the other curve

  3. Since the curves are both 2x2, there won't be any hole because the thickness (the diameter of the bevel object) is equal to the diameter of the main curve.
    To fix this simply scale the curve set as the bevel object down.

Note that the location and rotation of the bevel object does not matter, so you could position the bevel object like this to prove that the thickness of the torus is equal to the diameter of the bevel object:

enter image description here

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  • $\begingroup$ Thanks for this, scaling the object down does give me a torus. It does seem a bit hit-and-miss to make the object then re-size it though: I guess I expected the dimensions of the smaller circle to be respected in the cross-section. Thanks again. $\endgroup$ – user2950747 Dec 15 '13 at 22:40
  • $\begingroup$ @user2950747 They are. See my edits. Perhaps the scale of one of your objects is messed up in some way? Try resetting the scale on your main curve (Alt+S) $\endgroup$ – gandalf3♦ Dec 15 '13 at 23:24
  • $\begingroup$ Thanks – just added an update at the end of my question. Think the larger circle's scale was messed up. $\endgroup$ – user2950747 Dec 15 '13 at 23:29
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gandalf3's answer is the most likely answer and solution to the problem. Another thing you could try is shrinking the bevelled object with AltS. However, I see no advantages in obtaining a torus from curves that way. Why not just add a Curve > Circle and tweak the settings. To fatten, increase the depth and to get it smoother/rounder, increase the resoulution. Much easier to tweak and less work.

enter image description here

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    $\begingroup$ Thanks for the suggestion. That would definitely be easier (or even add a mesh torus), but I'd like to know why my approach produces unexpected results. If I can get that working, I've got a more complicated curve I want to use as an extrude path in the future. $\endgroup$ – user2950747 Dec 15 '13 at 22:24
  • $\begingroup$ @user2950747 Oh, thought you were just trying to get a torus from curves. Updated. $\endgroup$ – iKlsR♦ Dec 15 '13 at 22:25
  • $\begingroup$ Just to add a tip here: the rotation of the Bevel Object is irrelevant; if you insist on rotating the Bevel Object circle a certain way, and then doing Ctrl-A "Apply" + "Rotation & Scale": then you might end up with Dimensions X (or Y) as 0 - in which case the beveled object will be "flat" and not "cylindrical". The fix is to restore the X and Y dimensions both to be different from zero. $\endgroup$ – sdaau Sep 18 '14 at 21:01
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I have found this old question searching another thing on the internet... Both other answers by gandalf3 and iKlsR are good and fit to the question. This is just a little complement.

The bevel object is extruded with its center following the main curve and relatively to its vertices positions compared to its own center.

For instance, you can obtain the torus by shifting the bevel circle inner geometry :

enter image description here

  • Grab Y moves the curve and grab Z seems to do "nothing" :

enter image description here

  • And a try about rotations :

enter image description here

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