I'm trying to follow the following answer from the site: How to model the bottle threads?

I could do almost everything, but when I have to do the (spiral) loop cut the program doesn't allow me and I don't know why and in the answer there is no clarification of how it's done.

enter image description here

Additional info: Before I remove the screw (even after doing the knife intersect) I can do the spiral loop ring as the picture shows. When I delete it I cannot do the spiral loop cut nor select the linked objects all the spiral with CTRL+L and I have to do it manually.

enter image description here

  • 4
    $\begingroup$ Possible duplicate of Loop-cut won't go all the way around $\endgroup$ Sep 26, 2018 at 3:01
  • 2
    $\begingroup$ Did you do the Intersect(knife) step? find it in Ctrl-F menu. $\endgroup$
    – sambler
    Sep 26, 2018 at 6:00
  • $\begingroup$ Hi! Yes, I did the Intersect (knife) step, but when I select the rectangle and press Ctrl+R, it doesn't display the spiral $\endgroup$ Sep 26, 2018 at 14:42

1 Answer 1


I tried it myself. The problem is that not all of the vertices line up perfectly, so you end up with some rogue unwelded verts, like so:

enter image description here

See those little evil guys?

To fix it, select all verts and choose Mesh->Vertices->Remove Doubles. Then adjust the threshold until they all nicely merge.

enter image description here

Once all the verts are properly welded your spiral select will work.

  • $\begingroup$ Indeed that was the problem! Do you know why these ghost vertex appear? $\endgroup$ Sep 27, 2018 at 19:09
  • $\begingroup$ I think that the geometry of the spiral doesn't line up exactly perfect, even if it looks like it does, so the intersection cut adds extra vertices. $\endgroup$ Sep 28, 2018 at 3:44

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