3D Printing: Making watertight problem and non-fixed "Normals"

Cura is complaining that my models are not watertight and that the “normals” are not correct.

I have installed the Cura Plugin/Extension “Mesh Tools” and it is successfully fixing the normals and most of the “holes”.

However, my models don’t have “holes”. I am meticulous in their creation and most things are square, so there should not be any holes…although Cure Mesh Tools claims there are.

And, what are “normals” and why is Cura complaining about them, and why is Sketchup having this problem with “normals”?

Yes, again, I am meticulous that every edge matches up and connects perfectly, and I frequently will rebuild a section if there seems to be anything odd. So I am pretty convinced this is a Sketchup+Cura problem and not [likely] a problem with the model itself.

My 3D prints are correct when I use Mesh Tools to fix them and they often have problems without using Mesh Tools.

Is there an answer for this?

Yes, use Solid Inspector 2

Potentially the issue with normals is because your model has reversed faces, though I can’t say for sure without seeing it. The normal is a vector that points outward perpendicular to the front side of a face. A solid must have all normals pointing to the exterior of the object.

You can use SolidInspector 2 to check your object to see if it passes SketchUp’s criteria for “solid”.

I am unaware of faces facing on a particular direction. How do I set this direction in Sketchup?

My understanding was that surfaces/faces simply existed and not that they had a direction.

Faces have fronts and backs. The styles have different front and back face colors. By default, a blue-gray for the back. If you’ve applied materials to your model, exposed back faces can be masked. Set the face style to Monochrome so the back faces are shown. You can either select the reversed faces, right click on one and choose Reverse Faces or in many cases, you right click on a correctly oriented face and choose Orient Faces to fix the reversed faces.

The face orientation is importand because it tells the slicer software which side of the face is the printing material and which side is air.

FWIW, we frequently see questions about getting models right for 3D printing and the reversed faces thing is the problem. New users often start by drawing a rectangle and then detailing there model before making it 3D. For example, on the left I’ve done the newbie thing of trying to lay out the plan view of the thing before getting anything 3D. The faces are reversed and the bottom has no thickness.

On the right I made the bottom 3D before I outlined for the walls. When the walls get extruded the faces are automatically correctly oriented.

I always love a tool that has an “Outdated Signature” and that gives messages that essentially say: “There is some sort of an error, but we’re not going to show you where our give you any cues”.

The extension will show you where the holes are. Just hit Tab.

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And the outdated signature makes no difference.

How about sharing your SKP file so we can help you sort it out directly once and for all?