Subtracting solids, getting "nested instances"


#1

Continuing the discussion from Solid Inspector²:

Hi all:

I have the following extrusion 8"x12"x24" and am trying to punch a couple of openings into by subtracting the solid plugs. It used to work, now it doesn’t or is intermittent. Sometimes it works with the large plug, but not the small one.

I downloaded the Solid Inspector2, and it tells me that I have 3 nested instances when I click outside of the model. Googling hasn’t yielded any results. Any ideas? Model attached.

Sketchup 2015Pro in Windows 7 Home Premium on a Toshiba laptop with an Nvidia 250M

Thanks in advance … Norbert SenfFlue liner test.skp (1.8 MB)


#2

Because you have two groups and one component in the global context, SolidInspector counts 3 (nested) components.


#3

Thanks for the reply, Cotty. Unfortunately, I’m not versed enough to understand it.
I don’t understand what defines them as nested or why that is flagged as an error.
I changed one of the 3 original groups to a component, to see if it would make a difference, which it didn’t.
I created all 3 solids separately from scratch, not as copies, etc.
Why won’t it let me subtract one from the other, when I used to be able to do this? Or better yet, how do I do this?
Stumped…Norbert


#4

Each group or component for itself is a solid, so you can use the solid tools to substract the smaller ones from the big one. Several solids in the same context aren’t a solid per definition anymore.


#5

What do you mean by “the same context”. Would it help, for example to put one on a different layer, or import or copy if from a different model? How do I make them so they are not in the same context? …TIA…Norbert


#6

Layers in SketchUp do not separate objects into different contexts (unlike AutoCAD for example.)

SketchUp has the concept of entities collections (which translate into the Ruby API objects of the same name, and transparently to the native C++ collections “under the hood”.)

The model itself has a global entities collection.
Each group has it’s own entities collection.
Each component definition has it’s own entities collection.

To edit a group or component (that is to enter into an “editing context” of the object’s entities collection,) you double-click upon it with the mouse.

You’ll then see a dotted bounding box appear around the object’s entities.

If the object has nested groups or components, you can double-click on those also, entering a nested “editing context” of that object’s entities collection. And so forth …

To back out click outside the current editing context.


#7

So, back to the issue.

The entity objects of the “plug” groups, and the components, are in different contexts, and cannot intersect with one another.

The plug would probably need to be moved into (or just draw within,) the context of the component’s entities. Then move it into place intersecting the wall where you wish to Subtract the plug (1) from the wall (2).


#8

Thanks, Dan. I will try to wrap my head around those concepts and look for some reading material on it. I do come from 26 years in the Autocad world, and remember when the addition of actual solids into Acad was a big deal.
I suspect it is because this drawing is in the “component” directory - I can imagine how a component would be all one thing, and that you can’t use one part of it to subtract from another part…N


#9

So, I just noticed an interesting behaviour.
If I select first the intersecting plug, and then the large extrusion, and use the right click context menu “Solid Tools - Subtract”, it works.


#10

Back to the issue, I have no difficulty subtracting your solids. I don’t think context is relevant in to the issue (though in other cases it could be).

Your problem may be with the way that the Sold Tools subtract expects you to select things. It wants you to first select the solid to subtract and second to select the solid to subtract it from. When it is waiting for you to make the first selection, the cursor shows a little “1” in a circle. The cursor changes to a “2” when the tool is waiting for you to select the second solid. If you have something selected when you activate the tool, it will assume that is what you wanted to use for the “to-be-subtracted” and will go immediately to the “subtracted from” state. If you weren’t watching closely, that could produce confusing results.


#11

Using the Solid Tool - Subtract is two step operation.
Begin with nothing selected, and then activate the tool.
Click on the first solid to cut the second solid … “Use this to cut this.”