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Knife & Bisect Tools

BEGINNER
📖3 min read
Knife & Bisect Tools

Introduction​

The Knife and Bisect tools allow for free-form cutting of geometry. Unlike Loop Cuts, which follow the existing topology flow, these tools let you draw new edges exactly where you need them, regardless of the underlying structure.

Resources

Access guides on cutting geometry and topology redirection.

Links

Explore Blender's Knife and Bisect tools.

Videos

Watch tutorials on precision cutting and slicing.

Knife Tool (K)​

The Knife tool is used for precision surgery on your mesh.

  1. Activate: Press K. The cursor changes to a knife.
  2. Cut: Click on edges or vertices to define the cut path.
    • Snap: The knife automatically snaps to vertices and edge midpoints.
    • Constrain: Hold A to constrain the cut angle (e.g., 45 degrees).
    • Cut Through: Press C to cut through the entire model (backfaces included).
  3. Confirm: Press Enter or Spacebar to finalize the cut.
  4. Cancel: Press Esc or Right-Click to cancel.

Bisect Tool​

The Bisect tool cuts the mesh in half along a plane. It is often hidden under the Knife tool in the Toolbar.

  1. Select: Select the geometry you want to slice.
  2. Activate: Select the Bisect tool from the Toolbar (Long press the Knife icon).
  3. Draw: Click and drag a line across the mesh to define the cutting plane.
  4. Adjust: Use the Adjust Last Operation panel to:
    • Clear Inner/Outer: Delete one side of the cut.
    • Fill: Create a face along the cut.

Summary​

  • Knife (K): For drawing specific edges and redirecting topology.
  • Bisect: For slicing objects in half or trimming geometry.

Key Takeaways:

  • Always press Enter to confirm a Knife cut.
  • Use C with the Knife tool to cut through to the back.
  • Bisect is destructive if "Clear Inner/Outer" is checked.

Documentation for Methodology​

What to document when Cutting

In Your Method Section​

Describe why manual cuts were necessary. Was it to redirect edge flow or to cut a specific shape into a surface?

In Your Decision Log​

Record the following when using this technique:

  • Reason for cutting (e.g., "Redirecting topology around the eye socket")
  • Use of "Cut Through" (if affecting the back of the model)

Verification​

Knife cuts often create N-gons (faces with more than 4 sides). Check your mesh for N-gons if your pipeline requires quads. Ensure that "Cut Through" didn't accidentally slice geometry you didn't intend to.

Example Methodology Statement​

"The topology on the cheek was manually redirected using the Knife tool (K) to better align with the facial muscles. Resulting N-gons were resolved into quads."