Why does the size of objects affect boolean operations?

[xiombarg]

Does anyone know why larger sizes of objects tend to perform properly when doing boolean operations and small sizes have more of a tendency to leave missing faces and/or create artifact lines? I can't see why size would make a difference when doing these operations, especially when the measurements are set to mm?

[Trogluddite]

Hi there,
This is a well known SketchUp problem.
Although it will happily display objects of any size, it has problems making new geometry that is "sub-millimetre" in size.
I'm not quite sure what the technical reason is - I think is has something to do with the way that SU uses the OpenGL features of your graphics card to make life easier on your main CPU.
The usual way to deal with this is to scale up the thing you are making, do your edits, and then scale down again. I tend to scale by 1000 so that millimetres become metres - but smaller scale factors may work depending just how small your parts are.
A good tip (which I learned here of course!) is to make the thing you are editing into a Component. Copies of components will always share the same shapes, materials etc., but they can be scaled independently. By making your object a component, you can easily work on a scaled up copy positioned well away from other parts of your model. When you exit the component edit, the changes will copy across to your 'life size' original, and with no risk of accidentally moving it out of position, or accidentally selecting some other 'tiny' parts that you can't see when zoomed out.
An even lazier way is to just model everything at a larger scale (e.g. metres instead of mm), and then scale the whole model down when you need to export it, or take dimensions.

[xiombarg]

Thanks for the component tip Trog!

It's almost as if the formation of new edge geometry needs to be carried out one more decimal place in the formula in order to be recognized?

[TIG]

Sketchup/OpenGL have been optimized for the design of buildings - down to things like door-handles and up to thing like city-blocks.
If you try to model very tiny thing - like a swiss-watch, or gigantic objects - like a whole city, then you might well encounter issues or 'failed facets'.
Very tiny faces/edges or very gigantic face/edges might not get created as you might hope...

The solution is to group/make-component of the geometry you want to change... and scale it up x10 or x100 [or downwards if it's enormous!], then do the changes to create new geometry, which will then be successful, and finally scale down to the original size.

Very tiny/enormous geometry can 'exist', it's just the create of it initially that causes issues...

[Trogluddite]

There also a handy plugin from Liquid98 called "Boolean Helper" that gives you a couple of new toolbar buttons for very quickly scaling up and down - there's a choice of scale factors, and it even automatically zooms to make sure you can see everything when the size changes.
DOWNLOAD LINK