This is the first of two tutorials created with Blender version 4.2, where we’ll see some basic methods for cutting and separating parts of mesh objects in Blender.
Video Transcript
Hello everyone! This is the first of two tutorials created with Blender version 4.2, where we’ll see some basic methods for cutting and separating parts of mesh objects in Blender.
In this first part, we’ll look at the Bisect, Split, Rip, and Separate operators, which allow us to cut an object into two parts and separate portions of it, potentially creating a new Object from the separated parts, distinct from the original.
In the next part, we’ll see how to use the Boolean modifier, which enables non-destructive operations on objects.
In the next part, we’ll also cover how to display or render a section without modifying the object in any way, simply by setting the End Clip of the 3D Viewport or the virtual camera.
Let's start by separating some parts of an object using the Bisect operator, which allows us to cut a mesh into two parts along a cutting plane and is used in Edit mode.
First, select the parts of the object you want to cut. Bisect operates only on selected parts. In my case, for convenience, I’m selecting the entire object.
The Bisect operator is available in the Knife section of the menu on the left in a 3D Viewport, but you can also select it from the Mesh menu or, of course, access it through the Search window.
Once the tool is selected, click and drag to define the cutting plane.
Before executing the operation with Enter, you can move or rotate the cutting plane using either the interactive tools in the 3D Viewport or the tool's menu.
The geometry will then display a cut, as if we applied the Knife tool in a straight line on the selected parts.
The operator menu also includes the Clear Inner and Clear Output options, allowing you to remove one of the two parts of the object created by the cut. You can select both Clear Inner and Clear Output, leaving only the outline of the object along the cutting plane.
Finally, in the modifier tab, there’s also a Fill option, which allows you to fill in the geometry created by the cut; however, I have to mention that it doesn’t work well with certain geometries.
Let's now take a look at the Split operator, which is used in Edit Mode by pressing the Y key on a selection of elements, but it behaves differently depending on whether it’s used on edges or faces.
If used on edges, it creates a duplicate of the selected elements, but leaves this duplicate in place, so you’ll need to transform the copy somehow, such as by moving or rotating it, to notice its presence.
If you want to separate two parts of an object based on the selected edge loop while keeping the edge loop in both parts, as I’m showing on screen, you should use the Rip operator, whose shortcut is the V key.
Let’s go back to the Split operator because its behavior changes when used on a selection that includes faces. In this case, pressing Y will detach the selection from the rest of the object, but the boundary vertices will remain in both the original and the newly created part.
Here too, you’ll need to move or transform the selection in some way to notice the difference.
With both Split and Rip, the copies of selections or the separated parts are still part of the original Object.
Now, let’s move on to the Separate operator! This operator allows us not only to separate selected geometry from the rest of the object in Edit Mode but also to create a new Object, entirely separate from the original.
To use Separate, select the parts of the geometry you want to detach from the original, then press P and choose, in this first use case, the Selection option.
Blender will keep the original object selected, but by switching to Object Mode, we can select the new object created from the selection we just made.
Separate can thus be seen as a particular version of Split, as it allows us to detach part of an object and turn it into a standalone object.
As you may have noticed, the Separate operator’s menu offers two additional options.
The By Material option separates the different parts within the selection based on the sub-materials assigned to various faces; there isn’t much more to say about this mode.
The By Loose Parts mode is more interesting because it creates a different Object for each island of geometry, meaning each part of the selection not directly connected to the others.
In the 3D model I used for the examples, there are several parts not connected to the main model, and it could be useful to detach them entirely from the original to modify or replace them separately. I am selecting individual islands by pressing the L key, which is the shortcut for Linked, while the mouse cursor is over each island.
The operator acts only on selected parts, but in this case, I can select all the geometry and apply Separate By Loose Parts, resulting in many new objects.
The new objects created using Separate will have their Origin located where the Origin of the original object was, so most of the time, you’ll need to set their Origins manually to avoid incorrect behavior with rotations or other operations.
Okay, that’s it for this first part on Blender’s basic tools for cutting, slicing, and separating objects! See you next time!