Alright, bay leaf added to the soup and so let’s see.
First, some issues in your model as it is.
It’s a long way from the origin considering the dimensions of the thing.
Best practice is to keep the model close to the origin.
Next, modeling units. For what you are modeling you should have Display Precision set higher than you need in the final product so that you can see potential errors. Also turn off Length Snapping. That gets in the way of creating accurate and precise models.
FWIW, when I model for 3D printing I model with units set to meters and export the .stl in meters. Then import into the slicer in millimeters. This is on the printer as I type.
In SketchUp:
In the slicer:
dimensions in the lower right corner.
Next, about circles and arcs. First, make sure you drag out radii on axis. You are just randomly dragging them out. Easy to see with the recesses on the bottom of the feet. The guide lines pass through the center of the circle.
I would also suggest using some multiple of 12 for arcs and circles. For a circle, 96 is almost always plenty.
Next, you need to ensure your objects are solids. This means that every edge in the object is shared by exactly two faces, no fewer and no more. That means no stray edges, no holes in surfaces, and no internal faces. You have at least one stray edge (no faces) inside your model and you’ve got some internal faces.
So, as for what I did: I redrew your model from scratch. I made sure that circles were drawn on axis and there was nothing to prevent the thing from being considered a solid. You can see the difference in the geometry. I made the object a solid component (a group would also work but I don’t use groups)
Hopefully the next steps will make sense with the screen shot.
After that I extruded the tube (also redrawn) through the shield and made it a solid component. I trimmed the tube with the shield (and made a copy of the tube above so you can see it’s been trimmed.
I made a cylinder the same diameter as the ID of the tube as another solid and used it to cut a hole through the shield.
After editing the tube component and deleting the unneeded part, I used Union to combine the tube with the shield.
I use Eneroth Solid Tools from the Extension Warehouse for this because it respects components but you can do basically the same thing with the native Solid Tools.
Here’s the thing in the slicer.
And here’s the .skp file.
Lathe Vac.skp (559.3 KB)