I'm following BlenderGuru's tutorial Blender Beginner Tutorial - Part 5: Modeling

I'm trying to model a coffee cup. I started with a reference picture of the cup, added a cylinder, resized the base of the cylinder to match the cup, and resized the bottom of the cylinder to make the shape tapered.

However, when I add a loop cut to the middle of the cylinder mesh and scale that loop, the bottom edge loop becomes distorted and jagged for reasons I do not understand; it is no longer the nice ring that I want it to be.

enter image description here

What's going on?

  • $\begingroup$ when does the ring deform? when you release the new loop? or when you first click? $\endgroup$
    – Firewill
    Jul 3, 2017 at 23:42
  • $\begingroup$ You don't by any chance have proportional editing turned on do you? I can replicate that by enabling prop. editing and using Random as the setting. $\endgroup$
    – bertmoog
    Jul 3, 2017 at 23:47
  • $\begingroup$ The ring deforms when I scale the new loop. $\endgroup$ Jul 4, 2017 at 2:28
  • $\begingroup$ >I can replicate that by enabling prop. editing and using Random as the setting. That's got to be it. Of course! Its obvious now... It was set like that from the last demo - the frosting on the donut. $\endgroup$ Jul 4, 2017 at 2:29

1 Answer 1


You have Proportional Editing on with Random Falloff selected. You can turn this off by pressing O once or twice or by changing the menu manually at the bottom of the 3D Viewport.

A Gif to explain:

enter image description here

Proportional Editing can be extremely useful for deforming a mesh in a mathematically precise way. For example, with your coffee cup, I might loop cut the main cylinder several times and then use proportional editing with Smooth Falloff while scaling the bottom loop to create a loose conic shape. I then might use Sphere Falloff to widen the middle and shrink the top.

enter image description here

  • $\begingroup$ That's absolutely brilliant! Thanks for the help and the animated gifs! That was totally the culprit. $\endgroup$ Jul 4, 2017 at 2:31

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