Hi I have two solids. I wish to Union them. I am using Pro. When I union the surfaces get holes in them and they are not a solid any more.Rod End Thick Wall 6mm Hole.skp (1.1 MB)
A union of the round part with the hole fails.
Your model seems fine here. Just one solid.
(But maybe I misunderstand the issue. ?)
Cheers
It reports as a solid and it is a solid.
So you have failed to convince us.
What two solids ?
There is only one…
However, your object is quite small and includes some potentially tiny facets after an operation involving intersections etc [like solid tools, followme etc]. this might be your issue about missing facets ? SketchUp has a built-in tolerance of 1/1000". If a tiny line is shorter than that it is not created, because the two end points are deemed to be coincident. This has a knock-on effect, because the tiny face relying on that missing edge is not made and you end up with tiny holes. The established work around is to Scale everything by x100 [depending on the original size], do the operation. The edges/facets are now acceptably sized and get created. Then Scale down x1/100 back to the original size. The tiny facets can exist in the now original-sized version, but you cannot create them that small initially.
One 'trick' is to make the object a component and have two instances of it. Scale one x100 or x1000 as needed, edit the larger version and do your editing. Changes will be seen in the smaller version too. When you are done you can delete the larger version - there is no need to rescale anything. Keeping the original sized version with it's new tiny facets intact.
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Does Entity Info not call it a solid group?
This could be because SketchUp has a very loose (primitive but performancewise efficient) definition of a SketchUp solid (it’s very likely not invented by or specific to SketchUp). There exist edge cases of solids that are not covered by this definition, as well as not true solids that are recognized as solids. You have to consider that SketchUp displays volumes in Entity Info in real time for anything you select, without manual request. Doing more sophisticated checking for all the edge cases would take some more time.
However no matter what SketchUp displays, this has no impact on printability. It is printable if it is a true solid, a enclosed watertight not self-intersecting volume.
Just resize the model X1000 so that 1mm will be 1m and you will not have any difficulties with solid tools.Sketchup just don’t “like” small units.
Sorry folks. I uploaded the wrong model. However you seem to have homed in on the problem any way. Well done guys and thank you for your help.
This method really works. Thank you very much.
Here’s a method that may help you more.
Hello, et bonjour à tous, I come back with this old post. I didn’t manage to make my “pilastre” a solid.
The two parts of it are well solids, but for the union, maybe i did something wrong ?
I would like to understand…
Thanks by advance,
I tried to scale but it does not change the matter…
Pilastre.skp (606.4 KB)
In the scaled up version you have two components, the Pilastre finie et solide and Pied pilastre#1 each of which is solid and they are wrapped in the component called Pilastre avec base finie avec base creusée. That outer component cannot be solid because it contains components.
If you open the Pilastre avec base finie avec base creusée component for editing and Union the two components inside, that will result in a solid but the solid will still be inside the Pilastre avec base finie avec base creusée which will not be solid. You can explode the outer component after the Union step, though.
I used Union from Eneroth Solid Tools instead of the native Solid Tools because it respects components.
As @DaveR wrote, the two objects to be merged by Union must be in the same context and must be selected. You nesting has them in the same context, but you can’t select both at the same time without opening that component for edit:
Note: the pause in my animation is while I go of the capture window to access the union tool. You see the entity info change from two components selected to one group.
Edit: @DaveR you gotta stop editing to duplicate my animations while I am typing 
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Thank you Dave for your answer. I forgot to say that I’m a beginner and working with Sk free… so, no solid tool.
I understand in your answer that a solid can not contain 2 or more components ? But A solid has to be a component or a group, isn’t it ?
So i tried to explode my two components, and then move them “together”, and make from this a component, and at the second try, miracle !
Thank you for your help ! I’m a little bit less stupid, this evening…
Thank you to both of you. A last remark, always in sk free on web !
I have now two solids in my file, but the volume calculated by Sk is awfully different (1.0 MB)
I think that the one on the left is completely wrong, but why ?
Once again, sorry for my english ! Belgian french native 
My misunderstanding. You used the word Union and you were referring to solid components so I made the assumption you were using the Solid Tools.
Correct. At least for SketchUp to identify it as solid, it must be a group or a component. Also to be considered solid every edge must be shared by exactly two faces. No more and no less. So that means no stray edges, no holes, and no interior faces.
@philippe.j.lebeau, unless the interior faces together also form a manifold in the same editing context as the outer (surrounding) manifold. They need to be facing inward though, (fronts inside)
Thanks to all of you !