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I want to divide this model into separate pieces to prepare it for the next stage of a project. The divide needs to be made down a curved line (which I hope is visible in picture).

The model that needs to be divided,

I figured out how to cut it down a straight line a couple weeks ago, but apparently a curve is a different beast. Is there an operation for this, or do I have to manually make a bunch of straight cuts (or something equally painful)?

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3 Answers 3

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Although other answers are correct they all include unnecessary steps, you don't need to convert your curve to a mesh, nor do you need to extrude or joint anything, you can cut you mesh model directly from a curve using Knife Project operator.

enter image description here

For 2.8 + follow these steps:

  1. Create curve object for cutting and adjust it's shape
  2. Enter Edit Mode on the mesh object
  3. While in Edit Mode on the mesh, press the Ctrl key and select curve object
  4. Adjust the view as necessary, the cut is view dependent.
  5. Go to the Mesh > Knife Project menu, or use the Space Bar menu to search for the operator Knife Project
  6. Adjust settings if necessary from the redo panel (tool shelf or F9 key), Turn on Cut Through to cut all faces regardless of visibility.

For earlier versions

  1. Create curve object for cutting
  2. Select Curve object
  3. With curve still selected Shift select the mesh to be cut so it remains the active object
  4. With both still selected press Tab to enter Edit Mode on the mesh object
  5. Adjust the view as necessary, the cut is view dependent.
  6. Use the Space Bar menu to search for the operator Knife Project
  7. Adjust settings if necessary from the redo panel (tool shelf or F6 key)

Take care of the resulting topology afterwards, this will generate NGgons and overall improper topology unsuited for most end uses without further refinement.

Also adjust your viewpoint prior to cutting as the operator is view dependent.

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  • $\begingroup$ Could you go into more detail? I cant seem to reproduce this. $\endgroup$
    – Dontwalk
    Apr 12, 2016 at 20:09
  • $\begingroup$ Sure, just updated original answer with the steps necessary to reproduce $\endgroup$
    – Duarte Farrajota Ramos ♦
    Apr 12, 2016 at 23:04
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    $\begingroup$ This is great! In tests with Blender 2.77, I got best results when using a curve that was higher in preview detail (but judge for yourself if that is what is best for your particular project, and you can always try other detail levels). By default, Bezier Curves are set to a "Preview U" resolution of 12. I upped it to 24 and it cut cleanly through my cube like your example gif. $\endgroup$
    – Coby Randal
    Apr 12, 2016 at 23:23
  • $\begingroup$ @Duarte Thank you. For some reason this is only affecting one face of my default cube. $\endgroup$
    – Dontwalk
    Apr 13, 2016 at 11:47
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    $\begingroup$ Check the operator options in the bottom of the tools panel, there is a checkbox for "Cut through", that should do what you are looking for $\endgroup$
    – Duarte Farrajota Ramos ♦
    Apr 13, 2016 at 15:46
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Use the Knife Projection by selecting the curve then the object and activate it from the Tools Panel.

Knife project

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After converting the curve to mesh (as Omar Ahmad suggested) you may extrude it (E) through the mesh. Next joint the objects (Ctrl+J) and with the object selected in Edit Mode (with the Face selection type) press Ctrl+F-->Intersect (you may also press Space and type Intersect). Finally you can remove the curvy mesh and the redundant parts of the object. enter image description here

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