Knife tool is not cutting the ngons


I’m following a tutorial(23:48) and I’m trying to cut the bottom corners (ngons) of the chest (see red lines in png attachment) to turn them into quads. But when I do it, my Knife tool will not cut there. Why will it not cut?


Chest.blend (695 KB)

Right, the knifecut does not persist when going through existing vertices.
I personally would even rather select the 2 vertices and press “j” to connect them. More precise imho and works :wink:
For “fresh” cuts knife does as expected.


There’s double geometry. Select all, W -> remove doubles. The knife will cut just fine after that

Unlike mentioned in the video, you don’t have to make one cut at a time. Could add multiple by pressing E to end the cut and mark another one

Not only does it not work, that’s a bad advice with a wink. Filling an edge over an existing face with F creates a non-manifold error that is hard to find if one doesn’t know what to look for. The edge would connect the two vertices but wouldn’t cut the face, it would just overlap it.

Vertex connect path with J would cut the existing geometry.

Vertex connect path with J would cut the existing geometry.

Absolutely right, i confused “f” with “j”, sorry. Corrected in first post to avoid confusion.


Could you explain the “double geometry” a bit more? Late-night restaurant work, can’t think.

Thank you so much for your help!

Double geometry is multiple vertices in same location. I said geometry, because those vertices can be connected with edges, which in turn may be filled with a face. Knife won’t cut those without enabling cut through option, which you don’t want because as the option name implies, it will cut through the model, adding cuts on surfaces behind the one marked for cutting.

There are face indicators where edges should be (arrow) which means there are one or multiple 0 area faces. Moving the visible faces reveals more faces underneath. Removing doubles gets rid of those so the green face can be cut. There’s still overlapping geometry that won’t get merged or joined (red faces)

Remove doubles merges selected vertices in the same location, and it has merge distance option to adjust how close or far away the vertices have to be from each other for them to get merged. Removing doubles will leave one set of edges and faces instead of multiple.

These show one circumstance when double geometry is being created. I won’t link to the specific one because these are all helpful and you should watch them

Unlike other basics tutorials, these ones use actual terminology.

Okay, thank you very much!