Knife is a very useful tool that allows you to cut through the surface of a mesh to divide it into faces and edges, and generate new geometry (see Figure 6.14).
1. Press K. Alternatively, you can press Shift + K to affect only the selected geometry.
2. Left click, move your mouse to define the cut plane, and left click again. Repeat this process until you’re happy with the cut. The knife will show the points on-screen at which it’s going to add a vertex to the cut and, by default, the Knife tool will snap to vertices and edges. Press Shift to avoid that snapping and do a free cut. Press Ctrl to snap to the center of the edges.
3. Once you’re done with the cut, press Enter to confirm and apply the cut.
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