Knife Tool

Reference

Mode: Edit Mode
Panel: Mesh Tools
Hotkey: K or Shift-K

The knife tool can be used to interactively cut up geometry by drawing lines or closed loops to create holes.

Usage

When you press K (or Shift-K), the Knife tool becomes active.

Drawing the cut line
When using Knife, the cursor changes to an icon of a scalpel and the header changes to display options for the tool. You can draw connected straight lines by clicking LMB.
../../../../_images/knife1.jpg

Mesh before knife cut.

../../../../_images/knife2.jpg

Knife cut active.

../../../../_images/knife3.jpg

After confirming knife cut.

Options

Knife selection Shift-K
Activates the knife so only selected faces are cut.
New cut E
Begins a new cut. This allows you to define multiple distinct cut lines. If multiple cuts have been defined, they are recognized as new snapping points.
../../../../_images/knife4.jpg

Creating multiple cuts.

../../../../_images/knife5.jpg

Result of starting new cuts while in the tool.

Midpoint snap Ctrl
Hold to snap the cursor to the midpoint of edges
Ignore snap Shift
Hold to make the tool ignore snapping.
Cut through: Z
Allow the cut tool to cut through to obscured faces, instead of only the visible ones.
Angle constrain C
Constrains the cut to 45 degree increments.
Close loop: Double click LMB
This is a quick way to close the loop you’re currently cutting.
Draw a continuous line: LMB drag.
So you can draw a freehand line over a surface, points will be created at edge intersections.
../../../../_images/knife6.jpg

Constraining cut angle.

../../../../_images/knife7.jpg

Result of constraining cut angle.

Confirming and selection

Pressing Esc or RMB at any time cancels the tool, and pressing LMB or Return confirms the cut, with the following options:

Return will leave selected every edge except the new edges created from the cut.

Limitations

Cuts that begin or end in the middle of a face, will be ignored. This is a limitation of the current geometry that can be modeled in Blender.

Knife Project

Knife projection is a non-interactive tool where you can use objects to cookie-cut into the mesh rather than hand drawing the line.

This works by using the outlines of other selected objects in edit-mode to cut into the mesh, resulting geometry inside the cutters outline will be selected.

Outlines can be wire or boundary edges.

To use Knife Project, in ‘object’ mode select the “cutting object” first then shift select the “object to be cut”. Now tab into edit mode and press “knife project”.

Examples

../../../../_images/knife_project_text_before.jpg

Before projecting from a text object.

../../../../_images/knife_project_text_after.jpg

Resulting knife projection.

../../../../_images/knife_project_mesh_before.jpg

Before projecting from a mesh object.

../../../../_images/knife_project_mesh_after.jpg

Resulting knife projection (extruded after).

../../../../_images/knife_project_curve_before.jpg

Before projecting from a 3D curve object.

../../../../_images/knife_project_curve_after.jpg

Resulting knife projection (extruded after).

Known Issues

Cutting holes into single faces may fail, this is the same limitation as with the regular knife tool but more noticeable for text, this can be avoided by projecting onto more highly subdivided geometry.