I often design custom cases for various things. In this post I will describe how make them with Blender. Note: this is not about doing this the right or optimal way, but this is a way that works for me. 👍

For this you will need:

Step 1

Add a plane and modify it by subdivision/extrusion into the following shape.

SHIT+A -> Mesh -> Plane.

Step 2

Add a mirror modifier if you want to save work on symmetrical objects.

Add the Object modifier called Mirror.

Step 3

Modifiy the top and bottom edges to be marked as 100% creases:

Select the edges and then mark them as crease=1.0.

Step 4

Add a subdivision modifier to get round and smooth edges. Note, how the the creases are not rounded.

An Object modifier called Subdivision Surface. I usually use 3-4 subdivisions.

Step 5

Solidify your object. I tend to do most modeling with modifiers, which can be easily changed.

An Object modifier called Solidify. I usually select Even thickness and High quality normals in the options. Select your desired thickness. In this case I chose 1.8mm.

Step 6

Apply all modifiers, then loop cut the top edge to get two rows of faces.

Hit CTRL+R to activate Loop cut and slide, then hit enter to cut the top surface in half.

Step 7

Duplicate your object, one for the lid and one for the bottom half.

Hit SHIT+D to duplicate. Then SHIFT+ALT in face select mode to select the inner/outer row of rim faces.

Step 8

Extrude the inner/outer rim for your top/bottom halves of your container.

Hit E -> Z -> 2.5 to extrude the selected rim part towards the top by 2.5mm. I usually extrude the outer rim (top part) one layer (0.2mm) more than the inner.

Step 9

If you followed these steps you will end up with the two printable parts.

Hit TAB to toggle into object mode.

Step 10

Select both parts and export them.

You will need to install the export-selected plugin to export mulitple objects as one .STL file.