Correcting Non-Manifold Edges in Blender 3D Model for 3D Print I've built a 3D model of a sampling paddle (used to demonstrate random sampling to students of statistics) in Blender 3D, which I'm planning to use as my first endeavor into 3D printing.

During validation, I noticed that the model contains quite a few non-manifold edges (using Select > Select All By Trait > Non Manifold). However, I'm unsure how to proceed with fixing the model. Everything appears to be joined/connected, and I've removed/merged any duplicate vertices. I'd appreciate any advice so that I can move forward with my first print!

I used a cylinder to "punch out" the holes via a Boolean Difference operation.
One part of the problem is that you have internal faces which you should delete (see the first picture)
The problem at the circles can be solved with merge by distance
(previously called "remove doubles"). You might also try to recalculate normals (Ctrl+N)
The other pictures show that the borders of some faces are not
connected properly and how you can solve this.
When you see faces which are flickering ("face fighting") when you rotate view, you have two faces that are overlapping and sould delete one of them.




Happy Blending! :)