Need help separating a model cut with Zorro2 for 3d printing

I have a model that I need to cut in half at a precise location in order for it to be 3D printed correctly. I have used the Zorro2 extension to make the cut. The problem I’m having now is that I cannot seem to accurately separate the model into two pieces. No matter what angle I turn the model or how I drag the mouse to make the selection, I either select too much or too little.

This is something that I need to do often in 3D printing. Ironically, it’s much easier to do this in my slicer, because the slicing tool also closes all of the surfaces after the cut is made. Zorro2 only makes the cut, it doesn’t add interior surfaces (I wish it did).

I’ve attached the skp file. There are two copies of the model in it, the original and one with the slice. How do I select everything above the cut without also touching everything below it?

It also appears that it matters which direction I draw the mouse to make the selection. If I drag from upper-left to lower-right, I select fewer surfaces/edges than if I drag the opposite direction, even the selection box is the same. Is this expected?

I am using Sketchup Make 2017.
fume_extractor.skp (33.1 KB)

Yes, that’s great. But how did you do it? Like I said, I need to do this frequently for my models, so I really would like to know how to do it efficiently.

So you individually selected the faces and edges for each group? That’s exactly what I want to avoid. Since the model was sliced in half, I was hoping that there would be a simple technique to select everything in one shot. It seems that no matter what I do, I need to inspect the selection and manually tweak it for the missing or extraneous parts.

You can add in Fix101 if you really want to simplify it. You may not be aware that Zorro adds a context menu entry, Slice model at section. And fixit will put in the faces and remove any stray edges.

Very much so, this is a fundamental of sketchup. Left to right with a solid fence will only select what is within the fence, right to left with a dashed fence will select everything the fence touches.