Knife is not cutting between 2 edges

i`m finding the knife is cutting some parts of my model but not along the main vertical body/side anymore…
am I doing something wrong here?

well ur topology is ass backwards already… try triangulating your model, if ur not going to care about quads you might as well go full tri.

May i ask what you are trying to achieve?

(dont know why my text changed to this font either im very new to the forum and blender)… Ive only been modelling a couple of days just going through some cgcookie lessons and first time using the Knife tool, I seemed to be able to work it in the original cuts as you can see, but clicking on one edge and trying to click the other is producing no results, but the video is not telling me anything about this issue, hes just saying you can “click and cut” edges, points and across edges to create new edges and it will snap each time to each edge or point, which is what I was geting at first, but its just those 2 big side faces that are causing a problem.

so basically I can cut some faces but not others whats the thing to know here?
another example

Remember to press Enter when you are done cutting.

Side note, ive never used the knife tool ever in my 5 years of modelling, i dont find it essential at all. Anything the knife tool can do, other tools can do as well, and more often than not, easier.

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Looking at how messy this is, you probably have doubled vertices in there, or internal faces. Run remove doubles, then select all nonmanifold elements and fix them.

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ok thanks for the tip on other options fb,

I applied remove doubles, same problem,
What is nonManifold elements & how did I make an internal face? just a nutshell explanation i`ll work it out from there.

edit: found it >
“non manifold geometry”

ive ditched the model and tried again with good results so ill leave this issue for now.

some shapes can cut others cannot

You should never have that kind of geometry in the first place, its like you are trying to break blender. Since you dont seem to care about quads, just go full triangles as i said, and the knife tool should work.

Also, while in vertex select mode, look for any verteses that are by them selves on the middle of an edge, these should not be there.

ok I understand the importance of quads/tris and yes I will eventually care when I care to model something I want, but to give you the right perspective ive literally started any kind of modelling attempt from yesterday :rofl:and just got through my first few minutes of tutorials in this video set. I didnt know what a bevel/knife/loop cut was until last night.
i`m simply slicing a bit of geometry to test the knife tool I wasnt trying to “model something” :star_struck:

As a result of this ive found a plethora of information on non manifold geometry and related subjects on stack exchange so im gaining knowledge from my mistakes. You are talking like i`ve been modeling for months and dont respect quads. The video I was watching was simply showing the knife tool and how ngons are created and how we can fix that with other workflows in future videos. :sweat_smile: , BUT thanks for your help !! its appreciated.


You’re using ` mark as apostrophe instead of '. When you put text between two of those, it counts as preformatted text. So i`ve test test test tri`s, becomes ive test test test tris.

You’re also wasting your and everyone else’s time with unnecessary fluff in your posts instead of focusing on what is important. The problem description is not the most important part when asking help with a problem, it’s giving enough information and tools for others to find and communicate the cause of the problem.

What information is that? The same information you see and use to get to the problem you can’t solve. What that means in practice is using full interface screenshots to support your text description, and then preparing and uploading an example .blend of the problem. Ctrl+F3 in Blender to save a screenshot.

Don’t write text in images. You can highlight if something in the image is important but not obvious. You can also index them with numbers or letters if there are several, but text itself in images mean others can’t easily quote you, can’t translate, can’t do a web search of what you’ve written.

Use the time saved with that for preparing and uploading a .blend, because that is your main communication tool. That results to overall saved time for everyone. For example, this thread could start with one screenshot, one sentence, and one .blend file from you, and then getting the solution in post #2.

If you think ahead, what you’re showing in the screenshot can guide others for finding the problem area in your uploaded .blend by orientating the model and/or making same selections before saving the upload file. Again, without you writing anything. Can’t share the model? No problem, remove most of the geometry so it’s a set of polygons for troubleshooting instead of a whole asset.

  • File -> save as dialog has compress toggle on the left, which makes the .blend a .gz archive without renaming the file. Makes the file size smaller. User preferences have an option for it, if you want to make all files compressed
  • If you can’t upload here, try an alternate upload site like and share the link to the uploaded file.

JA sounds good i`ll do that from now on, didnt realize I could upload the .blend, that would be the easiest way and will do that moving forward. thanks for the advice.

Sorry I wasn’t around to explain! Yeah, nonmanifold geometry is just physically impossible surface discontinuities - like edges with three or more faces connected to it, or loose edges and verts that aren’t part of a polygon, or open edges that only have one polygon connected.

Most other modelling packages will prevent you from creating some of these in the first place, but since doing so is useful at times, Blender just trusts that you know what you’re doing :smile: .

A general tip on modelling: try to always use only quads, tris or (very rarely and only with sub-d modelling) pentagons in final meshes. Also try to keep the valency of your singularities at 3 or 5. Polygons with an arbitrary number of sides are useful for modelling of course, but they should always be used only temporarily, until you fix the topology into neat quads and tris.

(valency: how many edges are connected to a vertex; singularity: in a manifold mesh, a vertex with any number of edges connected to it that is different than 4.)

Some artists make it a point of pride to only use quads, and yes, in case you’re wondering, it’s almost always possible to do so, for any shape, but requires some foresight and planning. So go ahead and use tris, it’s OK :slight_smile:

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You’re welcome. Thanks for being open to the suggestion.

I know I sounded very direct about it, but that’s just my way of keeping the message clear but short, which is an achievement knowing how much I have to say about posting. But I do have couple of things to add:

  • File -> save as dialog has compress toggle on the left, which makes the .blend a .gz archive without renaming the file. Makes the file size smaller. User preferences have an option for it, if you want to make all files compressed
  • Not sure about the current forum limits, but if you can’t upload here, try an alternate upload site like and share the link.
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thanks JA, helpful hints will keep it in mind and have saved the pasteall link to my blender links. Thanks Piotr for the feedback!, quads, valency, singularities. Noted.