Creating 3d printable model - non manifold issues

Question

blend file

I am using a 3d model https://cults3d.com/en/3d-model/tool/ender-3-front-pi-case to create a slightly altered version of the Pi 4 Base stl (ie. the model with the Octoprint logo). I am attempting to reduce the logo size, add 18 vent holes and add a switch hole too. I know there are variants of this pi case but really would like to include the Octoprint logo. I have tried other variants of an Octoprint vented logo but they have been such a pain that this seems to be the simplest way.

To do this, I imported the "Pi 4 base" stl, reduced the size of the logo vertices on the x and z axis (leaving y ensures thickness of wall is intact), created solid vent shapes and a circle (called Yvents and Ycircle in my blender files) and used boolean difference to apply these to the Pi 4 base model (with the smaller logo already applied). The issue I have is this creates numerous manifold edges and, when I export the new model to a slicer (in my case VoxelMaker), supports are added everywhere I would expect except the vents, which I think is due to the non manifold issues. I have had so many issues with amending models using simple blender tools and the result being "damaged" 3d models, I feel like giving up on Blender altogether. I end up having to fix every dodgy edge, faces and vertices individually as Clean Up tools end up creating faces over designed gaps in the model walls. I have attached screen prints of the blender issues, plus how these appear in the slicer plus a link to a packed blender file. The problem model in the file is saved as "Pi 4 base small print". The original is "Pi 4 base".

Answer 1

You have three kinds of problems. Two are easy enough to solve:

1. There are some doubled vertices.

   • switch to vertex select
   • select all
   • M to bring up the merge menu
   • select by distance.

2. You have some interior faces.

   • Deselect all (short cut Alt–A
   • Use the Select → Select all by Trait → Interior faces menu entry to select the interior faces
   • X to bring up the delete menu
   • select faces from the menu

3. Some strange geometry around the vent in front. To see it

   • Deselect all (short cut Alt–A
   • Select → Select all by Trait → Non Manifold
   • result:

I don't know how you want to fix this, but if you zoom in on the vent you'll see that there are vertices that I think should be merged but aren't, for example:

There are a lot of verts and edges involved in this, so I didn't want to attempt it by hand; but I think you'll need to fix it before you can print.

EDIT: I've added my version of the file as it appears after step 3. The only remaining non-manifold geometry is selected.