The knife tool is one of the things I use most in blender. I use it to add vertices with out adding a Loop/cut/slide. I recently got a new laptop and installed blender on it, and it creates a random face when using the cut tool. enter image description here

Usually this is what I do to adda vertex, as you can see in the picture. enter image description here

But as you can see instead of only adding a vertex it connects to the corner of the object.

  • $\begingroup$ As for me it tends to create the best geometry it could, at least in given circumstances. I'm not sure how you could to cut line in the middle of the face without it connecting to one more vertice of the face. This is the same situation as with doing rectangle cut in the middle of polygon - new cut will be connected to 2 of 4 vertices of outer face. $\endgroup$
    – Mr Zak
    Apr 1 '16 at 23:31
  • $\begingroup$ I've always used the knife tool to add vertices without it making any extra edges or faces. $\endgroup$ Apr 1 '16 at 23:35
  • $\begingroup$ Use Alt+D with vertice selected where you'd like to add another one (you may want to slide added vertex for accurate positioning). I have to admit it isn't the best workflow as it doesn't create clean topology which you can handle with easily. $\endgroup$
    – Mr Zak
    Apr 1 '16 at 23:47
  • 1
    $\begingroup$ The behaviour was changed in 2.77 version, but strangely I wasn't able to find any documentation or mention in the release notes. Probably was made to speed up the cutting, sacrifing the vertex-adding functionality (btw covered by Alt + D and slide as said by @MrZak) $\endgroup$
    – Carlo
    Apr 2 '16 at 9:21
  • $\begingroup$ alt+ d only moves the current one for me $\endgroup$ Apr 2 '16 at 22:26

I think for what you want to do selecting an edge and choosing W > Subdivide may be a better less prone to failure workflow.

In you current case it is hard to tell from the screenshots why it is failing, it may be because of you current view angle. Try rotating the view more towards being perpendicular to the face normal.

Also in you case your geometry seems to be messed up, there are likely zero sized faces on the sides, overlapping edges, and probably two opposing faces on top and bottom. Try cleaning up your mesh by removing extra faces and duplicate geometry and removing doubles with W > Remove doubles and try using knife again after that.

  • $\begingroup$ It does it on every model, even a fresh blender file. Also I subdividing an edge does nothing for me $\endgroup$ Apr 1 '16 at 23:31
  • $\begingroup$ There may have been some behavior change in the latest blender version, not sure. Select an edge > W > Subdivide then you have to change to vertex mode, there will be a new extra vertex in the middle of the edge. $\endgroup$ Apr 1 '16 at 23:34
  • $\begingroup$ Thanks, that works but it will now be a lot more time consuming to add vertices :/ $\endgroup$ Apr 1 '16 at 23:39

The type of topology you are trying to create isn't supported by Blender. BMesh stores faces as a continuous loop of edges - branches and multiple loops aren't supported (yet).

If you try and create it by merging vertices you will find Blender ejects the edge from the face, creating a wire edge.

enter image description here


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