Tip: Using the Knife Modeling Tool in Blender

by Jonathan Williamson

Learn how to use the knife tool for advanced modeling in Blender through this quick tutorial by Jonathan Williamson.

In this quick tip we introduce you to the knife tool in Blender 2.6. The knife tool can be used for quickly adding new topology to your mesh in a flexible way. The knife tool acts much like a pen tool that allows you to draw in new vertices and edges exactly how you want them to create complex meshes.

By combining the knife tool with NGons in BMesh Blender provides an incredibly powerful modeling tool.

Using the Knife Tool in Blender 2.6

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Discussion

43 Responses to “Tip: Using the Knife Modeling Tool in Blender”
  1. Olson
    Posts: 6

    Thanks for this Jonathan. I would like to add that Space bar also confirms the cut, in the case that Enter is a bit annoying to reach across the keyboard for.

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    1
     Aug 17, 2012 at 9:33 pm
    • Olson
      Posts: 6

      I guess you said that already sorry.. :) I was confused as to why press enter rather than that

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      1.1
       Aug 17, 2012 at 9:36 pm
    • jerry perkins
      Posts: 39

      thanks!

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      1.2
       Aug 18, 2012 at 3:43 pm
  2. George Lakie
    Posts: 85

    Thanks for the new tut Jonathon. Good to know about the improvements to the knife system. Been a little busy studying coding, so picking up info like this is a major plus. Thanks again.

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    3
     Aug 17, 2012 at 11:00 pm
  3. Jeff Bessette
    Posts: 256

    I didn’t know about some of the other features like the snapping and being able to start a new cut. Was a big help!

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    4
     Aug 18, 2012 at 12:30 am
  4. steve
    Posts: 8

    i recently fell in love with the knife tool! just did a project where i started with a single plane and a brick wall texture, and i was able to go through and break up the wall into chunks and cracks by tracing along the mortar lines of the bricks. the uvs were preserved perfectly, and i simply cannot imagine how i could have accomplished the task prior to bmesh. love it!

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    5
     Aug 18, 2012 at 12:41 am
    • Jonathan Williamson
      Posts: 2945

      Ah yes, that’s something I forgot to mention in the tutorial. The knife tool preserves UVs perfectly in most cases, can’t beat that :)

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      5.1
       Aug 18, 2012 at 10:30 am
  5. ghansham chandel
    Posts: 83

    does ti take more time in rendering..?

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    6
     Aug 18, 2012 at 1:50 am
    • retasaur
      Posts: 27

      Not to my knowledge and I use this tool all the time.

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      6.1
       Aug 18, 2012 at 5:12 pm
  6. Sven Neubert
    Posts: 101

    thank Jonathan for this tip. Its a nice tool for created sharp edges on models. To create a hole in a polygon is the knife-tool not the best idea.

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    7
     Aug 18, 2012 at 2:02 am
  7. greg
    Posts: 115

    The knife tool and Ngons really lifts Blenders modelling tools up to 3ds max or maya’s in my opinion. You can now actually follow along to a 3ds max advanced hard surface modelling tutorial as happy as Larry, which is totally awesome.
    The only thing is how to find and remove any floating verts that are left at the end?

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    8
     Aug 18, 2012 at 4:27 am
    • Steve Hellman
      Posts: 15

      Hit “select” at the bottom (between view and mesh)and choose “loose verts/edges”. Once selected, delete.

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      8.1
       Aug 18, 2012 at 7:02 am
      • Jonathan Williamson
        Posts: 2945

        Ah yes, that’s an even better way than the “Adjacent number of faces” option I suggested before.

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        8.1.1
         Aug 18, 2012 at 10:34 am
    • Jonathan Williamson
      Posts: 2945

      Hi Greg,

      Generally you shouldn’t have any loose verts, but if you do you can select one of them and then press SHIFT+G > Number of Adjacent Faces. This will then select all loose vertices and allow you to delete them.

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      8.2
       Aug 18, 2012 at 10:32 am
  8. Dman
    Posts: 21

    Jonathan, nice to see the return of small focussed tutorials. I love the larger epic ones too, but sometimes I think that may place the pressure of an expectation of large scale efforts *all* the time on Blender Cookie.

    Lots of small, quick tips are very useful to me.

    Looking forward to what you make of the new skin modifier in 2.64. For organic forms it looks to be an awesome creature prototyping tool.

    What about some (simple!) tuts on Python, as in creating our own (again, only simple!) addons, and making custom changes to the interface.

    For instance, I recently saw a tut showing you how to create a custom mode where you can add mixed mesh selection modes, so you can select vertexes and edges in the same mode.

    It’d be great to see that kind of thing on BC.

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    9
     Aug 18, 2012 at 6:55 am
    • Jonathan Williamson
      Posts: 2945

      That’s a great suggestion Dman! I’m working on learning python right now and so I would love to do exactly this.

      Cheers,
      Jonathan

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      9.1
       Aug 18, 2012 at 10:32 am
      • jerry perkins
        Posts: 39

        Show us how to made the panel for the Clive rig! I am still reeling over how awesome it is that you made a panel that makes only the legs or upper torso visible!

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        9.1.1
         Aug 18, 2012 at 3:46 pm
  9. Peter Utinek
    Posts: 80

    thx for lots of modeling tips blender cookie is the best

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    10
     Aug 18, 2012 at 8:05 am
    • Jonathan Williamson
      Posts: 2945

      It wouldn’t be here without users like you to support it :) Your Citizen membership is what keeps this site running. Thanks!

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      10.1
       Aug 18, 2012 at 10:35 am
  10. riftmaster
    Posts: 32

    I had forgotten about the knife tool. Good to see the return of Quick Tips.
    I would love to see a series of quick tips about different addon tools. (for example the tool shelf addon Kent uses in his tutorials on this site.)

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    11
     Aug 18, 2012 at 10:30 am
    • Jonathan Williamson
      Posts: 2945

      That’s a good suggestion. Any other add-ons you’d like to see covered?

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      11.1
       Aug 18, 2012 at 10:35 am
      • antonioya
        Posts: 28

        Jonathan,

        And what about a QuickTip of how mix a Blender render and Cycles render?

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        11.1.1
         Aug 18, 2012 at 11:04 am
      • Jonathan Williamson
        Posts: 2945

        Since you’re a Citizen member check out my Interior Architectural Visualization series: http://cgcookie.com/blender/cgc-series/interior-3d-architectural-visualization/ Video #24 shows how to use the Internal for volumetric rendering and then combine it via the compositor and Photoshop with the Cycles render.

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         Aug 18, 2012 at 11:22 am
      • antonioya
        Posts: 28

        Thanks for the info :-)

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        11.1.2
         Aug 19, 2012 at 9:12 am
      • antonioya
        Posts: 28

        Jonathan,

        I have seen the video and I have one question. What would be the best aproach to create a glass sphere (made with cycles) but with hair ( I think cycles does not support hair). Is Photoshop the answer or do you think there is other options?

        Thanks!

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        11.1.3
         Aug 19, 2012 at 1:28 pm
  11. alec farai
    Posts: 146

    is it just me or does anyone hear that Jonathan Williamson is starting to have a deep bass sound in his voice

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    12
     Aug 18, 2012 at 11:38 am
  12. Chris Ferguson
    Posts: 66

    Quick Tips are Awesome! Thanks

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    13
     Aug 18, 2012 at 1:34 pm
    • Jonathan Williamson
      Posts: 2945

      Anything else you’d like to see?

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      13.1
       Aug 18, 2012 at 2:31 pm
      • Chris Ferguson
        Posts: 66

        How about something to do with Animation? I would say nodes, but I know nothing about what nodes do or are for as they relate to creating models for use in Unity/Game Engines.

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        13.1.1
         Aug 20, 2012 at 10:32 am
  13. Raphael Barros
    Posts: 11

    Hey, great tips, thx a lot! :D
    Do you know if there are any plans to make a “undo last cut” option? I think it’d be really handy (like the Interactive Split Polygon Tool from Maya).

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    14
     Aug 18, 2012 at 1:53 pm
  14. Joe
    Posts: 10

    You mentioned in this tutorial how to snap the vertex to the middle of the edge. How did you do that, you went too fast for me to follow.
    Thx

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    15
     Aug 18, 2012 at 9:06 pm
  15. Forc3
    Posts: 2

    Hey Jonathan, nice Tutorial thanks! ;) What about a product design Tutorial next time e.g. a custom smartphone? That would be really nice.

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    16
     Aug 19, 2012 at 2:20 am
  16. Nicholas Tindall
    Posts: 96

    I love the quick tips.

    Been using knife tool for ages now and love it; can’t believe I missed the c option though. :) Nice one as always.

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    17
     Aug 19, 2012 at 1:16 pm
  17. furlow
    Posts: 18

    When ever I use the knife tool, it Doesn’t seem to conect right. I have to go back and use Merge verticles when I cut lines.

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    18
     Aug 19, 2012 at 3:28 pm
  18. Zach Boatwright
    Posts: 7

    This. Is. Amazing. Thank you, Jonathan!

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    19
     Aug 20, 2012 at 8:37 pm
  19. philippe casteleyn
    Posts: 21

    Is there a reason why it says “Ignore snap (off)” instead of “Snap (on)”

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    20
     Aug 24, 2012 at 4:31 pm
  20. Gary Parkin
    Posts: 5

    Wow, I’ve been away for a while. This looks like a neat addition to Blender that I missed from 3ds Max.

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    21
     Oct 23, 2012 at 1:25 pm
  21. Gary Parkin
    Posts: 5

    Weird. My Avatar isn’t setting any longer.

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    22
     Oct 23, 2012 at 1:35 pm

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