You can use the Multi-Cut Tool to slice polygons along a straight plane, and then extract or delete faces above or below the cut. To slice a mesh using a custom plane Select the mesh or mesh faces you want to slice. Open the Multi-Cut Tool. (Optional) Set a live surface for the cut edges to adhere to. Click on either side of your mesh to define two slice points. An orange slice preview line appears between the slice points. This line represents the slice plane