How to cut STL models for 3D printing in Meshmixer

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It's obvious that models bigger than the print volume cannot be printed as one piece

Basic cuts along the Z-axis can be done directly and Slic3r

The solution is pretty straightforward

Just specify the height at which the model will be cut

You can also choose to rotate the bottom part upside down

After the cut the newly created model will be automatically placed on the virtual print surface

However, creating complex cuts in Slic3r can be challenging

as it's only possible to define the Z height of the plane cut

This may result in unwanted pieces of the model being cut off

We can demonstrate this problem by trying to cut one of Hulk's hands

Slic3r uses an infinite plane so even though the hand did get successfully cut

So did some other pieces, his leg and the stand

Meshmixer is a great tool for cutting models into smaller pieces

Let's start with a simple plane cut

Select Edit - Plain cut

Hold down the left mouse button to define a plane

Change the cut type to Slice so that no part of the model is discarded and confirm by hitting the Accept button

The model will still appear as one piece select Edit - Separate Shells to create individual models

Another option is to use the Select tool and specify a smaller area of the model to be affected by the cut

When we apply the plane cut everything outside of the selection will stay as one piece

Despite the plane i ntersecting the geometry as you can see in the lower part of Hulk's body

Again, we have to use the Separate Shells function, otherwise the model will still appear as one piece

Let's talk about aligning pins

Adding them will make it a lot easier to glue the finished parts together

First open the Objects browser and hide one part of the model created by the cut

Next up open the Meshmix menu and drag a primitive, a cylinder in our case, to the plane created by the cut

A gizmo with an arrow and a sphere will appear

You can scale the primitive by dragging the arrow and you can reposition it by dragging the sphere

Switch the composition mode to Create New Object

And when you're happy with the placement of the primitive confirm with the Accept button

We're gonna have to duplicate the model two times so that we'll end up with three copies of the primitive

Hide the two new copies in the objects browser

Next, click on Hulk's body and while holding down the Shift key click on the primitive a

A new menu with the boolean difference option will pop up

Untick Auto-Reduce Result, tick Use Intersection Curves and decrease Target Edge Scale

Meshmixer will show live preview of these changes

When you click on Accept the primitive will create a hole in the model

Now we just have to repeat the same process with the other half of the model

The Boolean difference consumes a copy of the primitive everytime we use it

That's why we made the two copies

This way, we'll still end up with one copy of the primitive left for export

Okay, we're done cutting. Now let's just export each of the models as STL

As you can see, because we added the aligning pins

The parts hold together even without any glue

And Hulk...